April 9-13, 2012 | San Francisco
Meeting Chairs: Lara A. Estroff, Jun Liu, Kornelius Nielsch, Kazumi Wada
Naturally occurred folding and unfolding systems such as self-assembled DNA bundles prove natural designs are hierarchical, with structures and property on multiple scales through interactions of subunits or building blocks. Mimicking these designs in fabrication of active materialsrequires a clear picture of energy landscaping that govern local interactions such as hydrogen bonding, van der Waals interactions, dipole-dipole interaction, capillary forces, etc, which will provide correct thermodynamic end points as well as facile kinetics for precise control of hierarchical structure for target function. To date, fabrications of active nanostructures have been conducted at ambient pressure and largely relied on these specific chemical or physical interactions. Here we show using Pressure-Directed Assembly (PDA) method we recently demonstrated, as an artificial tool, we can emulate natural folding and unfolding processes to explore energy landscaping that govern local interactions, to design new classes of active materials with structure and function that are not attainable for current materials, and to investigate new property resulted from the folding and unfolding processes. We show that under a hydrostatic pressure field, the unit cell dimension of a 3D ordered nanoparticle arrays can be manipulated to reversibly shrink and swell during compression and release of pressure, allowing precise tuning of interparticle symmetry and spacing, ideal for controlled investigation of distance-dependent energy couplings and collective chemical and physical property such as surface plasmon resonance. Moreover, beyond a threshold pressure, nanoparticles are forced to contact and sinter, forming new classes of chemically and mechanically stable 1-3D nanostructures that cannot be manufactured by current top-down or bottom-up methods. Depending on the orientation of the initial nanoparticle arrays, 1-3D ordered nanostructures (Au, Ag, CdSe, C60, etc) including nanorod, nanowire, nanosheet, and nanoporous network can be fabricated. Guided by computational simulations, we are able to rationalize the PDA of nanoparticle arrays for predictable nanostructures. PDA method mimics embossing and imprinting manufacturing processes and opens exciting new avenues for study folding and unfolding of active materials during compression (folding) and pressure release (unfolding). Exerting pressure-dependent control over the structure of nanoparticle or building block arrays provides a unique and robust system to understand collective chemical and physical characteristics. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energyâ?Ts National Nuclear Security Administration under contract DE-AC04-94AL85000.
Self-assembly of micro- and nano-scale materials to form ordered structures promises new opportunities for developing miniaturized electronic, optoelectronic, and magnetic devices. In this regard, several elegant methods based upon self-assembly have emerged, for example, self-directed self-assembly and electrostatic self-assembly. Dynamic self-assembly of nonvolatile solutes via irreversible solvent evaporation has been recognized as an extremely simple route to intriguing structures. However, these dissipative structures are often randomly organized without controlled regularity. In this presentation, we show a simple, one-step technique based on very simple â?ocoffee ringâ? phenomena to produce well-ordered structures (e.g., concentric rings, fingers, spokes, squares, triangular contour lines, ellipses, etc.) consisting of polymers or nanocrystals (NCs) with unprecedented regularity by allowing a drop of polymer or NC solution to evaporate in a curve-on-flat geometry. This technique, which dispenses with the need for lithography and external fields, is fast, cost-effective and robust. As such, it represents a powerful strategy for creating highly structured, multifunctional materials and devices.
The inorganic nanoparticles possess a range of tunable optical fluorescence or absorption properties depending on their chemical composition and their shape (semi-conductor (QD) and metallic gold) whereas the surface ligand can be optimized to tailor interactions with the surroundings. Their properties can be used collectively within nanostructured materials. Nanoparticles (QD, Au) are also ideal building blocks for the construction of ordered 3D structures. We present here different strategies to solubilise, chemically-functionalize nanocrystals into water and to organize them in a controlled manner at a macroscale. The first one is based on the self-assembling properties of synthetic gallate amphiphiles (Boulmedais et al, Langmuir 2006 ; Roullier, V. et al Chem. Mat. 2008; Amela-Cortes et al. Chem. Comm. 2011) and the use of controlled water drying to self organize the nanoparticles. In the second approach, biological molecules and molecular self-assemblies are used as templates to organize well-defined inorganic nanostructures. The interaction between anionic peptidic quantum dots and cationic vesicles results in the formation of either hybrid QD vesicles or a well-defined lamellar hybrid condensed phase in which the QDs are densely packed in the plan of lamellas (Dif A. et al J. Am. Chem. Soc. 2008). The addition of the well-known anionic actin protein to this system induced the formation of fluorescent 3D crystalline fibers. We demonstrate the ability of a self-assembled 3D crystal template of helical actin protein filaments and lipids bilayers to generate a hierarchical self-assembly of quantum dots (Henry E; Dif A. et al submitted to Nanoletters 2011). Functionnalized tricystein peptidic Quantums Dots, QDs, are incorporated during the dynamical self-assembly of this actin /lipid template resulting in the formation of crystalline fibers. The crystal parameters, 26.5x18.9x35.5 nm3 are imposed by the membrane thickness, the diameter, and the pitch of the actin self-assembly. This process ensures the high quality of the crystal and results in unexpected fluorescence properties. This method of preparation offers opportunities to generate crystals with new symmetries and a larger range of distance parameters.
The ability to control and direct self-assembly of nanostructures into specific geometries with new functionalities, while preserving their original optical and electronic properties, is an attractive research endeavor. We have fabricated liquid crystal (LC) based matrices into which chemically synthesized nanostructures of varied morphologies and compositions are uniformly dispersed. Using high resolution spatially- and time-resolved scanning photoluminescence (PL) measurements, we demonstrate directed nanoparticle assembly and manipulation in situ . In our first experiment, we demonstrate both directional assembly and electric field modulated re-orientation of disk-shaped gallium selenide nanoparticles using a nematic LC matrix. A comparison of the photoluminescence (PL) spectra of isolated nanostructures and of those suspended in the nematic LC shows that the PL peak for the latter is red-shifted by 37 nm, indicating increased inter-particle coupling. Spatial scanning PL maps of nanostructure-LC composite samples reveal this coupling can be further enhanced by the application of an in-plane electric field along the director axis which causes the LC order parameter to increase. In addition to the effect of inducing increased order in the ensemble, using polarization resolved PL scans, we demonstrate re-orientation of the nano-assembly by the application of an in-plane E-field perpendicular to the original director axis. The LC mediated inter-dot coupling also affects the dynamical properties of the nanoparticles by increasing the excitonic recombination rate which is both direction and electric field dependent. In our second experiment, we demonstrate spectral and polarization modulation of chemically synthesized core shell CdSe/ZnS quantum dots (QDs) embedded in a one-dimensional photonic cavity formed by a cholesteric liquid crystal (CLC) matrix. A Cano-wedge cell varies the pitch of the CLC leading to the formation of Grandjean steps. This spatially tunes the photonic stop band, changing the resonance condition and continuously altering both the emission wavelength and polarization state of the QD ensemble. Contrary to expectations, we find that the emission is elliptically polarized and that the tilt of the ellipse, while dependent on the emission wavelength, additionally varies with distance across the Grandjean steps. Our work open up the possibility of designing new QD based optical devices where spatial control of orientation, wavelength and polarization of the embedded QDs would allow great flexibility and added functionalities. This work was funded by NSF, UC MERI and UC MEXUS.  Verma, et. al., Phys. Rev. B, 82, 165428 (2010).
Damage-prone regions in structural composite materials are difficult to detect and even harder to repair. Damage is preceded by complex spatial and temporal changes in stress state, and it is therefore desirable to utilize these mechanical changes to activate â?" without human intervention â?" chemical changes that favorably alter materials properties when and where needed. Desirable properties brought about in response to damage or high-stress conditions include: (1) signal generation to warn of ensuing failure, (2) molecular structure modification to slow the rate of damage and extend lifetime (e.g., stress-induced crosslinking), and (3) repair of damage to avoid catastrophic failure (e.g., crack-filling and interface rebonding). To achieve these properties, composites must be designed to respond to changes at various length scales. At the atomistic level, chemical bond changes and conformational changes occur. On a supramolecular level, chain slippage occurs as a response to force and deformation. At the microscopic level, voids, cavitation, yield or crazing, and crack formation take place along with large scale viscoelastic deformation. This talk will describe molecular to macroscopic approaches to achieve self-healing functionality in polymer composites.
Our approach to engineer cellular environments is based on self-organizing spatial positioning of single signaling molecules attached to inorganic or polymeric supports, which offers the highest spatial resolution with respect to the position of single signaling molecules. This approach allows tuning cellular material with respect to its most relevant properties, i.e., viscoelasticity, peptide composition, nanotopography and spatial nanopatterning of signaling molecule. Such materials are defined as â?onano-digital materialsâ? since they enable the counting of individual signaling molecules, separated by a biologically inert background. Within these materials, the regulation of cellular responses is based on a biologically inert background which does not trigger any cell activation, which is then patterned with specific signaling molecules such as peptide ligands in well defined nanoscopic geometries. This approach is very powerful, since it enables the testing of cellular responses to individual, specific signaling molecules and their spatial ordering. Detailed consideration is also given to the fact that protein clusters such as those found at focal adhesion sites represent, to a large extent, hierarchically-organized cooperativity among various proteins. Moreover, â?onano-digital supportsâ? such as those described herein are clearly capable of involvement in such dynamic cellular processes as protein ordering at the cellâ?Ts periphery which in turn leads to programming cell responses.
The fabrication of structures with nanometric resolution is of great importance for the manufacture of next generation circuits, sensors and solar cells. [1,2] However, the top-down production of nanostructured materials often requires sophisticated equipment and takes place in specialized facilities, which increases the costs associated with the manufacturing process. By contrast, in biological systems the self-assembly of nanometric building blocks to yield micrometric and millimetric structures with a high order of hierarchical organization is a ubiquitous phenomenon that happens in mild conditions. Yet, it is difficult to control these self-assembly processes ex vivo to yield structures of controlled size and shape for their integration with standard technologies. For example, it is well known that collagen self-assembles to yield a plethora of structures with different dimensions and degree of hierarchical organization. However, it is difficult to harness this self-assembly process to obtain a single population of assemblies with a particular set of desirable features. To advance the current state of the art we have programmed the bottom-up assembly of biological building blocks to yield micrometric structures of controlled dimensions that bridge a pair of microfabricated electrodes. The key step of this methodology is to use alternating currents to concentrate and align collagen precursors to trigger their self-assembly at the gap between the electrodes so that hierarchically organized structures are obtained that are straightforwardly integrated with the circuit. By fine tuning the relevant parameters of the fabrication process it is possible to control the orientation and organization of the building blocks in the assemblies as well as the size of the resulting biomolecule collectives. The collagen bridges, fully integrated with the chip, can be used as templates for the growth of semiconducting materials as well as for the design of ultrasensitive sensors.  de la Rica, R.; Fabijanic. K. I.; Baldi, A.; Matsui, H. Angew. Chem. Int. Ed. 2010, 49, 1447-1450.  Aili, D.; Stevens, M. M. Chem. Soc. Rev. 2010, 39, 3358-3370.  de la Rica, R.; Velders, A. H. J. Am. Chem. Soc. 2011, 133, 2875-2877.  de la Rica Roberto; Mendoza Ernest; Lechuga Laura M.; Matsui, H. Angew. Chem. Int. Ed. 2008, 47, 9752-9755.
Nanostructured magnetic materials have attracted considerable attentions because of their novel potentials in biological and engineering applications. One of their interesting properties is that the magnetic nanoparticles in solutions can be aligned when an external magnetic field is applied. Such solutions containing magnetic materials, so called magnetorheological (MR) fluids or ferrofluids, are regarded as one of the smart materials. In magnetorheological fluids, important phenomena are inter-particle interaction and material adsorption that occur on the surface of the magnetic particles. Therefore, the surface morphology of the magnetic particles is one of the most important aspects that determine the functionalities of magnetic particles in magnetorheological fluids. To date, however, the spherical magnetic nanoparticle such as carbonyl iron (CI), magnetite (Fe3O4), maghamite (Î³-Fe2O3) particles or beads containing magnetic multicores with different surface layer have been mainly used as a stimuli-responsive materials under magnetic field. In this presentation, we report the magnetorheological behavior of nonspherical particles that have hierarchical structure and large surface area with an emphasis on the effect of the surface morphology on the viscoelastic properties of fluids under magnetic field. The fluids consisting of self-assembled iron oxide particles exhibit highly tunable viscoelasticity which is controlled by applying external magnetic field. The storage modulus of the hierarchical particle fluids is 2 times as large as that of the spherical particle fluid. A difference between hierarchical particles and spherical nanoparticles is explained by the fact that surface features of the hierarchical particles facilitate the self-alignment and increased the network strength between particles in the fluids. Compared with the smooth surface of the spherical particles, the rugged surface of the self-assembled particles fits well each other, which increases a resistance to the free motion of magnetic particles that are aligned by magnetic field.
We present a new concept in solution assembly: the non-polar solvent-driven micellization of a fully hydrophobic small molecule. Surfactants and amphiphilic polymers are known to form a variety of solution assembly states. However, for these conventional amphiphiles, the hydrophobic and hydrophilic parts differ greatly, with very different intermolecular interactions, which help drive assembly. Here, the following question is addressed: â?oIs it possible to generate micelles in solution using a small molecule using only van der Waals forces or Ï?-Ï? interactions?â? While recognizable micellization has been noted for hydrophobic long-chain di-block co-polymers (e.g. poly(styrene-b-isoprene), (e.g. Soft Matter 2009, 5, 1081) it was not observed until now in smaller, surfactant-like species. The chosen candidate was a C60-containing molecule that has previously been noted to form functional self-organized structures out of solution (e.g. Chem. Commun. 2010, 46, 3425). This hydrophobic amphiphile was observed to micellize in solution, with the extent of micellization strongly solvent-dependent. Small-angle scattering using x-rays (SAXS at SPring 8, Japan and an in-house beam-line, NIMS) and neutrons (SANS at SANS2D, ISIS, UK and D11, ILL, France) was used to build up a detailed picture of the micelle structure. In this presentation, we will discuss the control of micelle size and shape using solution parameters, with the aim to use this novel paradigm to generate functional systems.
The silver nanoparticles-clay thin films were fabricated by in situ reduction of silver nitrate in the presence of nanoscale silicate clays and subsequent water evaporation on glass. Upon the controlled thermal treatments, the generated Ag nanoparticles (AgNP) were observed to have high mobility into the film surface and further self-aggregation to form unique morphologies such as cube-, rod- and wire-like nano- to micro-meter sizes. The hierarchical transformation of these AgNP morphologies is largely influenced by the presence of nanoscale silicate platelets (NSP) that are previously synthesized by the exfoliation process of the natural clay stacks. The heating conditions and kinetic observation of the nanoparticle formation and morphological changes were investigated. The hybrids of AgNP/NSP) were prepared by annealing the film precursors at different temperatures (80, 150 and 200 oC) over a period of hours. It was observed by scanning electronic microscope for the kinetic migration of small AgNP between the clay layers and diffusion into the clay surface. On the surface, the AgNP further coalesced into hierarchical size and shape changes. The annealing conditions may affect the migration and morphology of the Ag particles for various compositions of AgNP/NSP at 1/9, 3/7 and 5/5 weight ratios. For example, a dynamic mobility of Ag to form hierarchical changes from spherical (diameter ~ 50 nm), to cubic (length ~100 nm), and then to rod-like shapes (length ~ 1.6 Î¼m and width ~300 nm). The thin clay film at 1.0 nm thickness may affect the dimensional growth of Ag particles in different directions, hence controlling the formation of various shapes such as spherical nanoparticles, cubes or further growing into lengthy rods. The manipulation of Ag particle morphologies and migration behaviors can be used for the fabrication of new Ag crystals for conductors and other applications.
1D nanomaterials such as high-aspect-ratio polymer nanopillars have received great attention as asymmetric structure because of their wide potential applications including Gecko-mimicking dry adhesives, microfluidics, water delivery, unidirectional wetting, nanotemplate, piezoelectric nanogenerators and micro-mechanical sensors. However, making nanoscopic structures with asymmetry is still a fascinating issue as both academic and industrial points of view. In most studies, nanopillars were fabricated by photolithography, e-beam lithography or soft lithography. But these techniques have the inherent limitation of manufacturing because of high cost, low throughput and the difficulty of making high-aspect-ratio. In recent years, anodized aluminum oxide (AAO) has become a challenging template system to overcome these limitations. Based on the self-assembly mechanism of the nanopore formation, AAO has uniform and hexagonally packed highly ordered nanoscopic pores with high-aspect-ratio. In addition, the diameter and length of AAO nanopores is easy to control by well established conditions. The general method to obtain high-aspect-ratio nanopillars from AAO includes the infiltration of polymeric materials into the nanopores and the dissolution of the AAO master template. In this method, removing master template restricts the recycling of the master mold. As a solution to this inefficiency, UV-curable polymers for mold casting might be applied. However, releasing the nanopillars from the mold is still difficult during the fabrication of high-aspect-ratio nanopillars because the difference of the surface energy between AAO and the polymer is small. In reference to these issues, we present a simple method of utilizing AAO as a reusable template for fabricating high-aspect-ratio polymeric nanopillars. Furthermore, our experiments include the method of manufacturing the bended or deformed structure of nanopillars to obtain more asymmetricity because 1D nanopillars still have the symmetric conformation based on the perpendicular plane against pillar axis.
We investigate electric field driven self-assembly of monolayers of charged gold nanoparticles suspended in a nonpolar solvent, hexane. Giersig and Mulvaney have reported electric field driven self-assembly of monolayers of gold nanoparticles (~20 nm) dispersed in water, as opposed to a nonpolar solvent (1). However, this mechanism for self-assembly has remained controversial, since evaporation and drying of colloidal nanoparticle solutions can also produce monolayers. Our nanoparticles are synthesized using the method of Martin et. al. (2). They are ~5 nm in diameter and stabilized with dodecanethiol. Electrophoretic mobility measurements indicated that the nanoparticles have a charge of â?"e or -2 e. These nanoparticles are injected into a parallel plate electrophoretic cell. One of the electrodes was a piece of copper with a surface area of 5.25 cm^2. The second electrode was a 3 mm carbon-coated copper TEM grid. The spacing between the electrodes was 0.3 cm. The nanoparticles were deposited on the TEM grid for imaging. Both the voltage and the exposure time were varied. The amount of deposited particles increased monotonically with an increase in voltage or time over which the voltage is applied. This indicates that particle deposition is not due to evaporative effects, but is driven by the electric field. For high voltages (20 V) and long depositions times (15 â?" 30 min), we observed large islands of close packed monolayers with dimensions up to a few microns. Within these monolayers, the nanoparticles self assemble due to a combination of the electric field, the steric barriers between particles, and van der Waals forces. This technique has potential for nanoparticle self-assembly on patterned substrates since the self-assembly is a parallel, rather than serial, process. (1) Giersig, M.; Mulvaney, P. Langmuir 9 (1993) 3408. (2) Martin, M. N.; Basham, J. I.; Chando, P.; Eah, S.-K. Langmuir 26 (2010) 7410.
Selective functionalization of nanostructures with nanometer resolution is important for the development of a broad range of applications ranging from single molecule electronics to advanced sensor technologies where the single molecule is used as the sensing unit. Today nano-scale functionalization is typically achieved using a combination of top-down lithographic techniques and chemical self-assembly. The resolution is therefore limited to the resolution of the lithographic technique- typically in the 30-100 nm range. Improved resolution and selectivity is highly desirable since it might lead to new opportunities in a broad range of applications ranging from single molecular electronics to sensor and nano-medicine. Hierarchical self-assembly would be an elegant way to fabricate multiple single molecule devices in a parallel way using chemical self-fabrication and photo-induced functionalization methods. Jain et al.1 have recently shown that the build-up of gold nanorod dimers with one molecule in between is possible and therefore it is a suitable approach towards the challenge of contacting single molecules by macroscopic wires. No pre-fabricated nanogap via lithography is necessary, since the nanogap is built up by the chemical synthesis and self-assembly of gold nanoparticles with the support of the molecule. By synthesizing new molecular bridges with functional chemical groups we hope to be able to use this approach to construct nanorod dimers attached to a single active functional molecule. Further functionalization of self-assembled molecules can be achieved selectively by highly efficient photocleavable protecting groups.2 Light directed synthesis on a photoactive SAM can provide micropatterns that can be used for array-based screening, solid-supported peptide synthesis, sensor and diagnostic applications. 1 Jain, T., Westerlund, F., Johnson, E., Moth-Poulsen, K. and BjÃ¸rnholm, T. ACS Nano, 2009, 3828-834. 2 Moth-Poulsen, K., Kofod-Hansen, V., Kamounah, F. S., Hatzakis, N. S., Stamou, D., Schaumburg, K. Christensen, J. B. Bioconjugate Chem., 2010, 21, 1056-1061.
Large area self-assembled monolayers of surfactant coated nanoparticles were fabricated on an aqueous subphase by controlling the evaporation of the colloidal solution carrier fluid.1 In this technique, nanoparticles were dispersed in a binary solvent mixture of toluene and hexane. The difference in solvent volatility and partial coverage of the trough leads to a flux of nanoparticles toward the evaporation front. The mass transport of nanoparticles continuously feeds the growth of monolayers to yield large area continuous monolayers. This technique has been used to successfully make monolayers comprised of oleic acid coated magnetite and manganese oxide nanoparticles, and alkane thiol coated gold nanoparticles.Monolayer formation is affected by the mixing ratio of hexane and toluene, the concentration of surfactant and the size distribution of the nanoparticles. The floating monolayers are transferred onto different substrates by the Langmuir-Schaefer method. Monolayer transfer is dependent on the interaction between the monolayer and the substrate, which is determined by surfactants in the monolayer and substrate materials. Nanoparticle bilayers were obtained by double deposition. These arrays had registry between the layers, with a number of different twist angles. This technique can be used to prepare large-area self-assembled nanoparticle monolayers. . T. Wen and S. A. Majetich, Ultra-large-area self-assembled monolayers of nanoparticles, ACS Nano, Article ASAP (2011), DOI: 10.1021/nn2037048
Lipid bilayer membranes (LBMs) as cell membrane mimics assembled on a solid electrode are an attractive platform for sensing protein-membrane or protein-protein interactions. In this work, LBMs were assembled on two conducting substrates â?" graphene and gold (Au). Graphene is a transparent and highly conductive electrode with biological compatibility. Graphene was grown on copper (Cu) by chemical vapor deposition by employing methanol as the precursor and pure Argon as the process/carrier gas without any added hydrogen. In the case of Au, the template stripping (TS) method was used to obtain atomically flat and pristine Au surfaces. This method has promise for large-scale tethered (t)LBM array manufacturing for high-throughput drug screening. 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles were deposited on graphene and Au surfaces and LBM formation and vesicle fusion dynamics were monitored using atomic force microscopy (AFM) topography imaging and force spectroscopy in a fluid cell under buffer conditions at room temperature. AFM topography images show sLBMs form on graphene with tubular features having relative orientation of 120 degree on Cu foils, while a uniform sLBM formed on graphene deposited on Cu single crystal. Interestingly, when POPC vesicles were deposited on highly ordered pyrolytic graphite (HOPG) surface, multilayers of LBMs form where the first layer of LBM is continuous, and the second layer exhibits tubular features with an orientation angle coincident with the step edge orientation of HOPG. These results suggest that the step edge of Cu below graphene may also guide the assembly of tubular LBM features. In order to assemble tLBMs on TS Au, POPC vesicles were functionalized with 2.5 mol% 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-poly(ethylene glycol)-2000-N-[3-(2-pyridyldithio)propionate] (DSPE-PEG-PDP), since POPC vesicle fusion does not spontaneously occur on unfunctionalized Au surfaces. Critical forces for vesicle rupture as a function of DSPE-PEG-PDP molar concentration in POPC vesicles on TS Au were examined using AFM force spectroscopy. The critical force needed to initiate tLBM of 2.5 mol% DSPE-PEG-PDP/97.5 mol% POPC formation is approximately 1.1 nN and that for 10 mol% DSPE-PEG-PDP/90 mol% POPC was approximately 0.5 nN. The lower critical force needed for tLBM formation with higher concentration of DSPE-PEG-PDP suggests that Au-thiolate bonding between DSPE-PEG-PDP and TS Au increases vesicle-substrate interactions promoting vesicle fusion. In contrast, higher forces applied during AFM tapping mode scanning of pure POPC vesicles on TS Au did not lead to observable LBM formation. Adsorbed vesicles remain on the surface, indicating that DSPE-PEG-PDP tethering molecules are needed to promote vesicle fusion on TS Au. These results show that both systems, LBM on graphene or on Au can be developed into a versatile platform for biosensing and drug-screening applications.
A combined layer-by-layer (LbL) surface amine amplification and electroless deposition process has been developed, for the first time, to convert biologically-replicable three-dimensional (3-D) nanostructured micro-assemblies (such as siliceous diatom frustules and beetle scales) into freestanding Cu-bearing or Ni-bearing structures that retain the starting biogenic microscale 3-D shapes and nanoscale patterns. After reacting the hydroxyl-bearing surfaces of these biotemplates with an aminosilane to introduce surface amine groups, an LbL polyacrylate/polyamine deposition process was used to dendritically amplify the surface amine concentration. Subsequent binding of metal chloride catalysts to these amine-enriched surfaces enabled the rapid electroless deposition of thin, conformal, continuous, and nanocrystalline or amorphous metallic coatings on the 3-D biotemplates. Selective removal of the underlying templates then yielded freestanding Cu-bearing or Ni-bearing structures. The conformality and continuity of the thin coatings, and the fidelity with which the biogenic shape and fine features were preserved in the freestanding structures, were significantly enhanced by the amplification of surface amines (and the associated enrichment of catalytic sites) resulting from the LbL polyacrylate/polyamine treatment. Monolithic and multicomponent structures (e.g., Cu, multilayer Au/Cu, CuO, and Ni-P alloy) with bio-derived morphologies have been synthesized utilizing this approach. This readily-scalable process may generally be used to convert self-assembled rigid templates (of biological or synthetic origin) into nanostructured transition metal- and noble metal-based microassemblies with a wide variety of selectable 3-D hierarchical morphologies for use in numerous functional and structural applications.
Naturally occurred folding and unfolding systems such as self-assembled DNA bundles prove natural designs are hierarchical, with structures and property on multiple scales through interactions of subunits or building blocks. Mimicking these designs in fabrication of active materials requires a clear picture of energy landscaping that govern local interactions such as hydrogen bonding, van der Waals interactions, dipole-dipole interaction, capillary forces, etc, which will provide correct thermodynamic end points as well as facile kinetics for precise control of hierarchical structure for target function. To date, fabrications of active nanostructures have been conducted at ambient pressure and largely relied on these specific chemical or physical interactions. Here we show using Pressure-Directed Assembly (PDA) method we recently demonstrated, as an artificial tool, we can emulate natural folding and unfolding processes to explore energy landscaping that govern local interactions, to design new classes of active materials with structure and function that are not attainable for current materials, and to investigate new property resulted from the folding and unfolding processes. We show that under a hydrostatic pressure field, the unit cell dimension of a 3D ordered nanoparticle arrays can be manipulated to reversibly shrink and swell during compression and release of pressure, allowing precise tuning of interparticle symmetry and spacing, ideal for controlled investigation of distance-dependent energy couplings and collective chemical and physical property such as surface plasmon resonance. Moreover, beyond a threshold pressure, nanoparticles are forced to contact and sinter, forming new classes of chemically and mechanically stable 1-3D nanostructures that cannot be manufactured by current top-down or bottom-up methods. Depending on the orientation of the initial nanoparticle arrays, 1-3D ordered nanostructures (Au, Ag, CdSe, C60, etc) including nanorod, nanowire, nanosheet, and nanoporous network can be fabricated. Guided by computational simulations, we are able to rationalize the PDA of nanoparticle arrays for predictable nanostructures. PDA method mimics embossing and imprinting manufacturing processes and opens exciting new avenues for study folding and unfolding of active materials during compression (folding) and pressure release (unfolding). Exerting pressure-dependent control over the structure of nanoparticle or building block arrays provides a unique and robust system to understand collective chemical and physical characteristics. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energyâ?Ts National Nuclear Security Administration under contract DE-AC04-94AL85000.
Simultaneous wide- and small- angle X-ray scattering (WAXS-SAXS) has revealed a stress-induced bimodal orientation of POSS crystals and PCL chains, both in a constrained POSS/PCL crosslinked network architecture with shape memory properties. POSS/PCL nanocomposites with molecular weight of 2,600 g/mol exhibiting shape memory behavior were synthesized and variation of crosslinker molar ratio was used to obtain POSS/PCL networks with different crosslink density (Alvarado-Tenorio et al., Macromolecules, 44, 5682, 2011). In that study it was shown that there are POSS crystals embedded in an amorphous PCL matrix, and the POSS crystals were ordered in a cubic nanostructure. In this work, it will be shown that elongation at room temperature of all the networks yielded a double-induced orientation (90 and 180 degrees) of the POSS crystals, as indicated by the 101 reflection. Moreover, it was also detected stretched-induced crystallization of the otherwise amorphous PCL chains. Furthermore, SAXS data showed long periods in the meridional and equatorial orientations of 630, 90 and 45 Angstroms corresponding to a lamellar nanostructure of PCL chains. The induced bimodal orientation of the POSS-PCL molecular network will be correlated with its shape memory properties.
Driven by potential applications such as bioelectronics, wearable electronic devices, and robotics; the field of elastic conductors acquired renewed importance. In the last decade, tremendous research and development efforts have been invested in exploring the functionalities envisioned for carbon nanotubes (CNTs) with various elastic substrates. The adoption of CNTs was primarily driven by its high aspect ratio that resulted in composites with high conductivity during stretching. Common elastic conductors from CNTs, however, have several problems; such as high quality of composite is not often reproducible, higher conductivity is unlikely, and properties are anisotropic. In order to improve the current design of elastic conductors, we need to design nanocomposite materials that have superior properties and functionalities than current materials. To satisfy this requirement, we present elastic conductors from extreme content of nanoparticles (NPs) with polymer matrix by layer-by-layer (LBL) assembly technique and a method of filtration. Nanocomposites from LBL assembly have superior electromechanical properties as well as chemical stability. From a classical chemical standpoint that a dispersion of NPs can be easily aggregated by polymer solution of a different charge was expected and the aggregate was obtained by filtration to yield films. It is thus an intriguing engineering question to compare properties of nanocomposites by two methods. NPs, in general, might be an inadequate choice as fillers because they do not have as high aspect ratio as CNTs, however specially synthesized NPs with judiciously chosen polymer matrix are expected to have superior electromechanical properties and dynamics of the composite and these are rarely studied. It is therefore important to understand the basics of the charge transport in our composites containing such a high content of NPs, which obviously make them quite superior to traditional composites. Overall, successful outcome of this research project will be a significant step forward in terms of both exceptional properties and unique material design.
Silicon compounds have been widely used then extended to nanotechnology area. We introduce a use of silicon elastomer attached with a photocurable self-assembly group as stamp materials in soft lithography. 'Soft lithography' is an alternative technology of conventional UV photolithography, which has attracted much attention in â?~pattern transferâ?T and â?~microfabricationâ?T by making stamps, molding, and contact-printing processes due to its low-cost and easy processability, for use, particularly in plastic/molecular electronics. The resolution of soft lithography technique relies on the elastomeric elements. Since commercially available silicon elastomers often results in collapse and mergence due to their low mechanical strength, especially in the nano-scale regime(<100 nm), these limitations have motivated us to develop a new stiff, photocured silicon elastomers, with a photocurable self-assembly functionality. Using the designed silicon rubber materials, we demonstrated its unique capability for the case of nano-striated features of 300 nm width and 600 nm height in photoresist, which is one of the most challenging â?~nano-patterning tasksâ?T in advanced soft lithography. We also demonstrated â?~elastomeric photopatternsâ?T in the ~5 micrometer resolution range using a new photocurable, stiff silicon rubber prepolymer.
A highly flexible and adaptable two-dimensional metal-organic coordination network (MOCN) is synthesized from rod-like 4,4'-di-(1,4-buta-1,3-diynyl)-benzoic acid (BDBA) and Fe atoms on Au(111) and Ag(100) surfaces and studied by scanning tunneling microscopy under ultra-high vacuum. The network grows continuously over multiple surface terraces through mutual in-phase structure adaption of network domains on terraces and at step edges. The adaptability of the MOCN to intrinsic surface defects is mainly ascribed to the high degree of conformational flexibility of the butadiyne backbone of the ligand. Furthermore, the selective interaction of transition metal atoms with distinct functional groups of the ligand molecule enables the fabrication of surface confined MOCN decorated by atoms of the second metal. Since Fe forms strong coordination bonds with the carboxylate groups and Ni shows a high affinity to the butadyine backbone, the Fe-BDBA coordination network provides a robust host for Ni atoms that is thermodynamically stable even at temperatures above 380 K. It is found that the substrate plays a significant role in the incorporation of Ni atoms in the organic matrix. On Au(111) only the decoration of phenyl rings was observed whereas on Ag(100) the Ni is located near the butadiyne backbone presumably embedded in the first substrate layer. The incorporated Ni atoms can be utilized for the catalytic conversion of gas molecules, and serve as stable nucleation centers for metal clusters as well as for the selective binding of further ligands into the network cavities. The presented results open the way for the designed hierarchical assembly of complex functional structures at surfaces.
We have studied the synthesis of organic-modified metal oxide nanocrystals [1-3] by simply performing hydrothermal synthesis in the presence of organic molecules. The organic molecules that were tethered on the nanocrystals controlled the surface chemical character and enabled better handing of nanocrystals including the longer colloidal stability, reduced viscosity of concentrated dispersion, and the mixing with polymers at higher concentration. In addition to these merits, we believe that the surface modification of metal oxide nanocrystals provides novel strategies to realize new functions and properties of metal oxides. We found that the organic molecules on the surface of metal oxide nanocrystals enabled their ordered assembly. In this presentation, we report the self-assembly of metal oxide nanoparticles through coordination functional groups that are displayed on the surface, focusing on cubic assembly of octahedral primary CeO2 nanoparticles [4,5] and superparamagnetic behavior of the assembly of Fe3O4 nanoparticles with the size of up to ~500 nm.  This result might lead to the assembly of several kinds of nanocrystals to realize the hybridization of various functions of metal oxides.  S. Takami, et al., Mater. Lett. 61, 4769, 2007.  M. Taguchi, et al., Cryst. Growth Des. 9, 5297, 2009.  M. Taguchi, et al., CrystEngComm 13, 2841, 2011.  S. Takami, et al., Dalton Trans., 5442, 2008.  S. Asahina, et al., ChemCatChem 3, 1038, 2011.  T. Togashi, et al., Dalton Trans. 40, 1073, 2011.
Well arrangement and construction of different low-dimensional nanomaterials (e.g. zero-dimensional (0D) nanoparticles (NPs), one-dimensional (1D) nanotubes, nanowires, nanorods, and two-dimensional (2D) flakes) as building blocks with two or more levels from the nanometer to the macroscopic scale leads to the formation of three-dimensional (3D) hierarchical nanocomposites with unique properties. Here, we reported the self-assembly of a family of 3D hierarchical nanocomposites of carbon nanotubes (CNTs) and layered double hydroxides (LDHs) by direct chemical vapor deposition. Co-precipitation was firstly involved to synthesize LDHs from metal cations and interlayer anions. CNTs were assembled into the composite by chemical vapor deposition (CVD) of carbon sources, such as methane and ethylene. A hierarchical nanocomposite with the structure of single/double walled CNTs interlinked with two-dimensional flakes is constructed via in situ CNT growth onto LDH flakes . Both wall number and diameter of the CNTs and composition of the flakes can be easily tuned by changing the proportion of transition metal in LDH flakes. Furthermore, continuously interlinked CNT layer alternating with lamellar flakes structure is obtained after the compression. The hierarchical composite is demonstrated to be excellent filler for strong polyimide film. This kind of hierarchical nanocomposite can also be mass produced in a fluidized bed reactor. Three-dimensional (3D) micro-coiled or nano-coiled materials have attracted extensive attentions because of their unique conformations and outstanding mechanical and electromagnetic properties. Reduction of FeMgAl LDH flakes can lead to the formation of layered double oxides (LDOs) with high density Fe nanoparticles embedded on both sides. Aligned double/multi-walled CNTs can synchronously grow and extend perpendicularly from both sides of the LDO flakes. With the continuous growth of the CNT arrays, the array further will assemble into CNT double helices. The intercalation of MoO42- can lower the catalyst particle size and improve its density. As a result, single-walled CNT double helices can be successfully synthesized on the MoO42- intercalated FeMgAl LDHs. The CNT double helices are with good extension characteristics and the CNT yarns in the double helices are able to carry high current . This double helical structure provides a platform towards the design of hierarchical nanocomposites that can be used in areas such as high-performance CNT yarns, nanoelectronics, magnetic devices, and energy conversion. References:  a) M.Q. Zhao, Q. Zhang, X.L. Jia, et al: Adv. Funct. Mater. 20(2010), 677â?"685; b) M.Q. Zhao, Q. Zhang, J.Q. Huang, et al: Carbon 48(2010), 3260-3270.  a) Q. Zhang, M.Q. Zhao, D.M. Tang, et al: Angew. Chem. Int. Ed. 49(2010), 3642-3645; b) M.Q. Zhao, Q. Zhang, W. Zhang, et al: J. Am. Chem. Soc. 132(2010) 14739â?"14741.
Biomolecules can be used to control the interface and assembly of inorganic materials. This is particularly effective in materials science for the assembly of complex nanostructures, protein-nanoparticle interfaces, and hybrid nanocomposites as well as in the production of materials with enhanced optical, catalytic, and electrical properties. Protein cages have been explored for use in the synthesis, assembly and functionalization of nanomaterials due to their well-defined morphological and chemical composition. Site-specific modification of protein cages using genetic engineering allows for targeted functionalization and directed assembly onto surfaces. Here we describe the use of engineered ferritin protein cages designed to bind to aluminum nanoparticles (nAL). Metals such as nAL contain and release a large amount of stored energy due to their chemical composition and size. Unfortunately, energetic properties of nAL are often limited by the mass transport and diffusion distance of reactive components. These engineered protein cages can be loaded with oxidizing agents and bought in close proximity to the nAl surface, thereby leading to increased combustion kinetics and energy output from nAL. Additionally, the combination of biologically derived iron oxide with nAl is chemically equivalent to thermite and represents a new type of bio-thermite material.
Nature generates thousands of millions of complicated and subtle structures via the process of natural selection. Many of these nano/submicrometer structures are functional units, and are far beyond the capability of human design. In the past decade, we have been focusing on using this natural wealth to fabricate a broad range of novel functional materials with morphologies of natural organisms like butterfly wing scales, egg membranes, bacteria, and plant fibers, et al. In this presentation, we will demonstrate how these natural structures can be replicated in various functional materials including oxides (ZnO, ZrO2), sulfides (CdS), and metals (Au, Ag, Cu), with their original bio-morphologies inherited. We will show as well how these novel materials can be beneficial to fields including light manipulation, gas sensing, and surface enhancement of Raman scattering, et al. Accumulated results have proven a substantial and applicable route to fully utilize the natural morphologies, yielding materials and solutions otherwise unavailable.
Controlling the self-assembly of colloidal nanorods to form large-scale â?~nano-carpetsâ?T of vertically aligned rods represents a promising route towards making printable solar cells and photoelectrochemical devices. In addition to potential increases in production speed and savings in production costs, such nanostructured devices could allow for improvements in light absorption over bulk materials. Semiconductor nanorods, including heterostructures, can now be made from a wide range of materials, and cm2-scale films of aligned rods have been assembled in the laboratory. However, large films typically have defects including cracks, voids and multilayers, and are difficult to make reproducibly. This talk will present recent insights from molecular dynamics and Monte Carlo simulations into the conditions under which such films form, including the effect of the rod-rod interaction length-scale and strength, and the effect of the solvent-air and solvent-substrate interfaces. We show that the rod-rod interaction determines whether multilayer or single-layer crystals nucleate and grow in solution. Further, we find that a subtle balance between the rod-rod and rod-interface interactions determines whether nucleation occurs in solution, on the substrate, or at the air-solvent interface, and whether it occurs with the rods oriented parallel or perpendicular to the interface. We argue that the majority of assemblies formed to date are metastable kinetic products, and as such will suffer from defect and reproducibility issues. Instead, we propose a new way to make dense, uniform, and large-scale monolayer films using conditions for which they will be thermodynamically stable in solution.
Biological structures are hierarchically structured across multiple length scales. This complex and specific organization leads to physical properties and functions that are not achieved by the basic components alone. Cells are capable of sensing their environment from the nanoscale to macroscale making the structure-function relationships in natural tissues of great interest for designing biomaterials. In the past several decades, researchers have demonstrated the potential of electrostatically driven self-assembly as a powerful tool to achieve hierarchies across the nano-, micro-, and mesoscale. Strong interactions between polyelectrolytes and oppositely charged self-assembling peptides have been shown to induce complex formations that result in highly ordered structures. Utilising these concepts to design tunable self-assembling systems is an attractive strategy towards synthetic scaffolds that mimic the hierarchical organisation of biological tissues. We have designed and synthesized polymer-peptide hybrid molecules that self-assemble into nanostructures including nanofibres in aqueous solvents and contain peptide sequences that bind specific glycosaminoglycans (GAGs). GAGs offer a unique advantage of being highly charged polyelectrolytes that play a role in binding growth factors and regulating cellular events. Peptides were synthesised manually using standard solid phase Fmoc synthesis techniques and purified using high performance liquid chromatography (HPLC). Poly(caprolactone) (PCL) was modified with a maleimide isocyanate using reported procedures followed by coupling of the peptide via a cysteine to the maleimide group. The conjugation steps were confirmed by 1H-Nuclear Magnetic Resonance Spectroscopy (NMR), and the nanostructure morphologies were observed by transmission electron microscopy. The polymer-peptide conjugates complex with the GAGs to form hydrogels with hierarchical features across length scales. Changing the length of the hydrophobic PCL block affects the polymer-peptide nanostructure morphology, which also influences the supramolecular assembly with the GAGs. Specific binding of the GAGs introduces an additional functionality to manipulate the structural organisation. This system provides a platform to study how hierarchical structure and presentation of biologically relevant components affect cellular behaviour.  (a) Stevens MM; George JH. Science 2005, 38, 1135-1138. (b) Place ES; George JH; Williams CK; Stevens MM. Chem Soc Rev 2009, 38, 1139-1151.  (a) Capito RM; Azevedo HS; Velichko YS; Mata A; Stupp SI. Science 2008, 319, 1812-1816. (b) Carvajal D; Bitton R; Mantei JR; Velichko YS; Stupp SI; Shull KR. Soft Matter 2010, 6, 1816-1823. (c) Chow LW; Bitton R; Webber MJ; Carvajal D; Shull KR; Sharma AK; Stupp SI. Biomaterials 2011, 32, 1574-1582.  Annunziato ME; Patel US; Ranade M; Palumbo PS. Bioconj Chem 1993, 4, 221-218.
The current research has been focused on the synthesis of nanomaterials with controlled size, shape and their assembly into hierarchical structures. Herein, various TiO2 hierarchical microstructures have been fabricated by a facile hydrothermal method using water-soluble titanium complexes as precursors . Particularly, flower-like particles, titania hollow spheres, and nanorod-based microspheres have been synthesized. The growth and assembly process of these hierarchical structures were elucidated in view of capping mechanism, ligand-assisted dissolution, chelation-assisted assembly and oriented attachment. Titania materials were synthesized by a hydrothermal method using water-soluble titanium complexes as precursors and additives as shape-controlling or structure-directing reagent. Firstly, flower-like particles were synthesized using titanium-glycolate as precursor and picolinic acid as capping reagent. Secondly, hollow TiO2 spheres were fabricated using titanium-oxalate in the presence of excess ligand that played a role as etching reagent. Finally, a sulfuric acid additive was used to control the assembly of nanorod-based microspheres. The preferential adsorption of picolinic acid via chelation to Ti on (111) plane of rutile rather than (110) plane due to the matching of distances between Ti-Ti atom (6.5 Ã.) and that of the mutual Ï?-stacking between the aromatic ring (6.0-7.0 Ã.) resulted in growth of pyramidal branches in flowerlike particles. The self-assembly of microspheres was driven by the reduction of surface energy coupled with chelation effect. Ligand-assisted dissolution is responsible for the hollowing process, resulting in the formation of the hollow structures. The morphology evolution of the hierarchical microspheres followed several steps including the formation of 1D structures, assembly of the primary nanocrystals into bundles, and oriented attachment growth.  Tomita, K.; Petrykin, V.; Kobayashi, M.; Shiro, M.; Yoshimura, M.; Kakihana, M. Angew. Chem. Int. Ed., 2006, 45, 2378.
The pattern fabrication of the self-assembled monolayers (SAMs) is important to produce more delicate functionality by the spatial distribution of functional groups on various surfaces. Inkjet printing is versatile in aspects of high speed, relatively simple process, low cost, compatibility with a wide range of substrates, and ability to deposit very small droplets. Recently the inkjet technology has been recognized as one of the most promising technologies for soft electronics. However, the inkjet-assisted patterning needs more fundamental understandings to be applied in wider fields. In this work, we report fast and large-area SAM pattern fabrication controllable by an inkjet-print self-assembly method which combines inkjet printing and SAM techniques. By means of controlling process conditions such as solution concentration, dispensing speed, and humidity etc., optimized patterns were well produced. The resulting inkjet-print SAM patterns of 3-aminopropyltriethoxysilane and 3-triethoxysilylpropyldiethylenetriamine with surrounding octadecyltriethoxysilane SAM were confirmed by AFM, FTIR spectroscopy and contact angle meter. These inkjet-print SAM patterns were also applied to further selective immobilization of various functional organic and inorganic nanomaterials.
Tissue engineering strategies typically utilize either peptide or polymer hydrogels as bio-mimetic scaffold carrier materials . Hydrogels provide mechanical support for cells and can easily be combined with bioactive moieties to help elicit a desired cellular response. Polymer hydrogels have tailorable mechanical properties but often suffer from being synthesised from synthetic monomers and having to be polymerized in situ . Peptide based hydrogels are formed via self-assembly which gives rise to very unique properties and results in them having the ability to be used as injectable systems, with gelation occurring simply through the addition of salts . Furthermore, they degrade into natural occurring amino acids and biomolecules can be easily incorporated which offers advantages in terms of bioactivity, but fundamentally they suffer from quick degradation rates and have low failure strains3. Here we present a novel and alternative hybrid polymer-peptide gel system consisting of a poly (Î³-glutamic acid) (Î³-PGA) polymer network physically cross-linked via grafted self-assembled Î²-sheet peptide sequences. Î³-PGA is a naturally occurring enzymatically degradable homo-polyamide, it is highly biocompatible and water soluble . This system provides a gel made entirely from natural peptide bonds, with a polymer network providing tunable mechanical properties and predicted high failure strains. Biomolecules can easily be incorporated and tailored for a given application via abundant and unmodified â?"COOH groups situated on the polymer backbone and also, being designed to gel through self-assembly it can be used as an injectable system. Î²-sheet peptide sequences were synthesised using a manual solid phase Fmoc peptide synthesis technique. Purity was confirmed by HPLC and Mass Spectroscopy. The peptide sequences were grafted to Î³-PGA in the presence of diisopropylcarbodiimide and the degree of peptide conjugation was estimated by HPLC. The hybrid polymer-peptide material was dissolved in water and the solution pH increased by addition of NaOH, causing immediate self-assembly and the formation of a gel. Rheological experiments were used to investigate the mechanical properties, and to verify the predicted high failure strains of the hybrid hydrogels. These reached up to 40% strain before failure, eclipsing typical failure strains of peptide self-assembled hydrogels. Following repeated material failures the hybrid polymer-peptide gel was left to re-assemble and managed to recover 90% of its storage modulus. The secondary structure and pH responsivity of the hydrogels was observed through circular dichroism and Î²-sheet formation was confirmed via fluorescent spectroscopy after binding to Thioflavin T.  Place, Evans, Stevens. Nature Materials 2009.  Burdick, Anseth. Biomaterials 2002.  Greenfield, Hoffman, Olvera de la Cruz, Stupp. Langmuir 2010.  Kubota H, Nambu, Endo. J Polym. Sci. Part A Polym. Chem 1993.
Current progress in self-assembly and material genomics has spawned a growing interest in morphology control for higher efficiencies and structural stability in thin film devices. Further, recent experimental evidence suggests that substrate patterning may be an elegant means for obtaining this desired control. When applied to the field of organic photovoltaics, substrate patterning may provide a promising approach in fabricating a more tractable donor/acceptor composition gradient, and therefore, a higher efficiency device. However, current challenges in experimental efforts include the inability to decipher the complexities of morphology evolution as well as limitations on resources and time. Thus, the use of a computational framework, to predict morphology evolution during solvent-based fabrication techniques, will add significant value to the predominantly experimental community. Developed for high throughput analysis of morphology evolution during solvent-based fabrication of organic solar cells, this framework includes modeling of evaporation-induced and substrate-induced phase separation. In this way, we can successfully quantify the effects of substrate patterning on morphology evolution. In particular, we are interested in examining various one and two-dimensional patterning motifs aimed towards constructing a detailed phase diagram. Subsequently, this provides a quantitative means for understanding morphology evolution undergoing substrate induced phase separation, and a recipe for self assembly control. These developments yield detailed tuning capabilities for producing morphologies that display favorable intrinsic characteristics in the context of organic solar cells, and thereby produce higher efficiency devices.
Encapsulation of drugs within nanocarriers that selectively target malignant cells promises to mitigate side effects of conventional chemotherapy and to enable delivery of the unique drug combinations needed for personalized medicine. To realize this potential, however, targeted nanocarriers must simultaneously overcome multiple challenges, including specificity, stability and a high capacity for disparate cargos. We recently developed a new class of hierarchical nanocarriers termed protocells that synergistically combine features of mesoporous silica nanoparticles and liposomes. Fusion of liposomes to a spherical, high-surface-area, nanoporous silica core followed by modification of the resulting supported lipid bilayer (SLB) with multiple copies of a targeting peptide, an endosomolytic peptide and PEG results in a nanocarrier construct (the â?~protocellâ?T) that, compared with liposomes, the most extensively studied class of nanocarriers, improves on capacity, selectivity and stability and enables targeted delivery and controlled release of high concentrations of multicomponent cargos (chemotherapeutic drugs, siRNA, dsDNA, toxins, etc.) within the cytosol or nucleus of cancer cells. Specifically, owing to its high surface area (>1000 square meters per gram), the nanoporous silica core possesses a higher capacity for therapeutic and diagnostic agents than similarly sized liposomes. Furthermore, owing to the substrateâ?"membrane adhesion energy, the core suppresses large-scale membrane bilayer fluctuations, resulting in greater stability than unsupported liposomal bilayers. Interestingly, the nanoporous support also results in enhanced lateral bilayer fluidity compared with that of either liposomes or SLBs formed on non-porous particles. We show the enhanced fluidity yet stability of the SLB enables dynamic reconfiguration of the surface allowing membrane bound ligands to engage in complex multivalent interactions with the target cell. The synergistic combination of materials and biophysical properties organized over several hierarchical length scales enables high delivery efficiency and enhanced targeting specificity with a minimal number of targeting ligands, features crucial to maximizing specific binding, minimizing nonspecific binding, reducing dosage, and mitigating immunogenicity.
In this presentation I will introduce our recent advances in the self-assembly of superparamagnetic colloidal building blocks for the fabrication of magnetically responsive photonic nanostructures. The superparamagnetic iron oxide colloidal particles are essentially self-assembled clusters of small nanocrystals that are synthesized by using a high temperature hydrolysis reaction. Another self-assembly process occurs when these superparamagnetic colloids are exposed to external magnetic field, allowing the formation of chain-like nanostructures with regular interparticle spacing of a few hundred nanometers along the direction of the external field so that the system strongly diffracts visible light. The balance between attraction (magnetic dipole interaction) and repulsion (electrostatic force) dictates interparticle spacing and therefore optical properties. By changing the relative strength of these two forces, we can tune the peak diffraction wavelength over the entire visible spectrum. We demonstrate a number of interesting applications ranging from color displays to security devices, and color printing that are made possible by the taking advantage of the fast, reversible response and the feasibility for miniaturization of these magnetic responsive photonic nanostructures.
Solution self-assembly of superparamagnetic nanoparticles is driven by short-ranged magnetic dipolar interactions. Interesting situations occur if the sizes of the nanoparticles are so small that they become comparable to the range of magnetic interactions. In this regime nanoparticle self-assembly delicately depends on size, shape, thickness of the stabilization layer, and strength of external magnetic fields. We show by using dynamic light scattering, cryo-TEM, cryo-SEM and synchrotron small-angle x-ray scattering, that small cubic nanoparticles with thin stabilization layers self-assemble into very long strings and highly ordered meso-crystals of sizes of seveal micrometers, that can be oriented in external magnetic fields. Spherical nanoparticles and cubic nanoparticles with thick stabilzation layers do not self-assemble under similar conditions, allowing control of the magnetically induced self-assembly process via size, shape and layer thickness of the nanoparticles. Control of magnetic self-assembly of nanoparticles is vital for their use in magnetic resonance imaging, where solution self-assembly and aggregation of nanoparticles has to be controlled to maximize relaxivities and thus imaging contrast. We further show that the attachment of brush-like polymer layers completely suppresses nanoparticle aggregation in nanocomposites. This opens for the firs time a versatile route to fully miscible nanocomposites. We demonstrate that highly filled nanocomposites can be made that show ordering of nanoparticles into well-defined fcc-lattices. Control of interparticle distance is possible via the molecular weight of the attached polymer chains (1). S. Fischer, A. Salcher, A. Kornowski, H. Weller, S. FÃ¶rster, Angew. Chem. Int. Ed. 50, 7811 (2011)
The magnetic properties derived from the nanoscale self-assembly of poly(styrene-block-ethylene oxide) (PS-b-PEO) copolymer thin films blended with L10-ordered FePt nanoparticles (NPs) are investigated. In this communication, we reported the morphological change induced by the introduction of FePt nanoparticles on the phase behavior of PS-b-PEO thin films. We find that the increase of the unit cell due to the presence of nanoparticles leads to close-packed planes of spheres with an ABAB stacking which are more stable than the cylinder phase observed for the neat PS-b-PEO copolymer thin films. The stability of a square-packing phase for a particular film thickness is also discussed since this morphology is advantageous for microelectronic applications. Macroscopic study of the magnetic property reveals a distinct hysteresis with a coercivity value of about 100 Oe at 300K, which constitutes the first example of block copolymer/nanoparticle nanocomposite thin films having magnetic property at room temperature. At the nanoscopic scale, magnetic signals observed on MFM images indicate, in accordance with TEM images, that L10-ordered FePt NPs functionalized with short dopamine-terminated-methoxyl poly(ethylene oxide) chains are localized within the spherical PEO domains. In order to increase the 2D long-range order of the sphere array, we also present self-assembled PS-b-PEO/FePt nanocomposite thin films confined in microfabricated polymer trenches. The use of patterned substrates permits to decrease the density of dislocations and disclinations which favor the accumulation of nanoparticles (small aggregates) within their core defects in order to minimize the conformational entropy loss associated with the PEO chain stretching. An important application of this work extends to potential future bit-patterned magnetic-storage media.
Integration of diverse nanostructured components into single nanoparticle system enables the development of multifunctional nanomedical platforms for multimodal imaging or simultaneous diagnosis and therapy, which provides synergistic advantages compared to individual component materials, such as real-time non-invasive monitoring of drug delivery and biological responses to the therapy. We reported on the fabrication of monodisperse magnetite nanoparticles immobilized with uniform pore-sized mesoporous silica spheres for simultaneous MRI, fluorescence imaging, and drug delivery. We synthesized hollow magnetite nanocapsules and used them for both the MRI contrast agent and magnetic guided drug delivery vehicle. We reported the fabrication of novel alginate capsule-in-capsules (CICs) containing iron oxide and gold nanoparticles and human pancreatic islets for simultaneous immunoprotection and multimodal imaging.
Peptides and proteins are hierarchically structured nanoscale assemblies with well-defined atomic-level structures. As materials, they possess structural and catalytic functionalities that are unmatched by any synthetic counterparts to date. Hybrid biomaterials based on synthetic polymers and natural building blocks have the potential to combine the advantages of both components and overcome the inherent limitations, such as the ease of degradation, loss of functionality, and difficulty in processing for biomolecules. With recent advances in our fundamental understanding of protein science, especially in designing peptide/protein sequences to achieve properties similar or superior to their natural counterparts and in developing synthetic methods to modify proteins in a controlled manner, these building blocks present numerous opportunities to create soft materials to meet current challenges in life science, energy and environment. I will discuss our recent efforts in design and synthesis of amphiphlic peptide-polymer conjugates toward engineering modular organic nanoparticles as nanocarriers. Stable, multi-functional organic nanoparticles that combine long in vivo circulation, the ability to cross vessel walls to reach tumor tissues and controlled disassembly/degradation for eventual clearance will have a significant impact in nanomedicine. However, it remains a significant challenge to simultaneously control the nanoparticle size in the range of 10-30 nm, enhance particle stability and tailor disassembly at the timescale suitable for nanocarriers. We have advanced this goal by designing a new family of amphiphiles based on coiled-coil 3-helix bundle forming peptide-polymer conjugates. The resultant monodispersed nanoparticles are composed of subunits, < 4 nm in size, that form a highly stable 15-17 nm diameter particle and demonstrate an in vivo circulation half life-time of 28 hrs, minimal accumulation in the liver and spleen and effective urinary clearance. Based on these studies, I will discuss some opportunities this new family of soft matter presents as well as challenges to advance this emerging field.
Magnetic field is as an effective stimulus to guide the rapid assembly of superparamagnetic colloidal building blocks into one-dimensional dynamic photonic chains within one second. Each chain, with periodical interparticle spacing in the range of 100 to 200 nm, acts as the smallest 1D photonic unit and strongly diffracts visible light. The structural color of the photonic structures can be dynamically modulated across the whole visible light range by changing the interparticle separation or the orientation using an external magnetic field. We also demonstrate the assembly of superparamagnetic Fe3O4@SiO2 particles in a spatially patterned magnetic field, which allows one to change the orientation of the particle chains, dynamically producing a high contrast in color patterns. In principle, magnetic fields can be used to dynamically modulate the color of each pixel, making our magnetically responsive photonic system a new platform for chromatic applications, such as reflective color display, antifraud, camouflage.
DNA is an attractive platform for nanotechnology applications because of its size, specificity, and designability. However constructing DNA-based platform that can do work is difficult. We have developed a DNA-based cross-shaped nanoactuator system that cycles between an extended and contracted confirmation relying on strand displacement reactions. The actuator contains 4 structural strands with two unique DNA â?ozipperâ? sequences. Each zipper sequence employs traditional adenosine-thymine nucleotides as well as non-traditional inosine-cytidine nucleotides. The I-C bond consists of only 2 hydrogen bonds as opposed to the typical 3 hydrogen bonds found in G-C bonds. The actuator is extended by inserting two ssDNA which are the natural complements to the zipper sequences. The natural complements have a stronger binding affinity to one side of the zipper than both zipper strands have to each other, thus unraveling and allowing the actuator to extend. The two contraction strands contain sequences which are a natural complement to parts of the opening strand. When they bind to the extension sequences, the zippers are able to rebind and this contracts the actuator. Proper assembly and function of the devices was confirmed using fluorescent DNA gel electrophoresis, AFM imaging, and time-lapsed fluorescence.
Hard particles are known to organize due to entropy alone, and simple crystals, liquid crystals, and even quasicrystals have been reported in the literature. However, the role of entropic forces in connection with building block shape is not well understood. We present the results of a comprehensive computer simulation study of the thermodynamic self-assembly and packing of facetted particles. We report hierarchical assembly of both disordered and ordered structures for certain facetted shapes. We show how the self-assembled structures can be understood as a tendency for the particles to maximize alignment of their facets, which can be generalized as directional entropic forces.
In part I of this talk on meso-origami we present studies of hierarchical assemblies of graphene. Graphene is the ultimate thin film with a single layer atomic layer thickness and features unique electronic, thermal, and mechanical properties. The flexibility and strong attraction between graphene layers promotes the formation of self-folded nanostructures, which can be assembled into various hierarchical geometries. In this talk we present an overview of recent atomistic and continuum modeling of tearing, folding and assembling graphene sheets into functional materials. We study the self-folding of mono- and multilayer graphene sheets, utilizing a coarse-grained hierarchical multiscale model derived directly from atomistic simulation. We extend the analysis to a systematic study of the conformational phase diagram of graphene sheets, and we derive a conformational phase diagram for rectangular graphene sheets, defined by their geometry (size and aspect ratio), boundary conditions, and the environmental conditions such as supporting substrates and chemical modifications, as well as changes in temperature. We discover the occurrence of three major structural arrangements in membrane, ribbon, and scroll phases as the aspect ratio of the graphene nanoribbon increases. In part II we present an analysis of folding and assembly of amyloid protein materials at varied scales. Amyloids are highly organized protein filaments, rich in beta-sheet secondary structures that self-assemble to form dense plaques in brain tissues affected by severe neurodegenerative disorders (e.g. Alzheimerâ?Ts Disease). Identified as natural functional materials in bacteria, in addition to their remarkable mechanical properties, amyloids have also been proposed as a platform for novel biomaterials in nanotechnology applications including nanowires, liquid crystals, scaffolds and thin films. We use a coarse-grain model to analyze the competition between adhesive forces and elastic deformation of amyloid fibrils, focused on the formation of self-folded nanorackets and nanorings. We investigate the effect of varying the interfibril adhesion energy on the structure and stability of self-folded nanorackets and nanorings and demonstrate that such aggregated amyloid fibrils are stable in such states even when the fibril-fibril interaction is relatively weak, suggesting a strong propensity towards aggregation, given that the constituting amyloid fibril lengths exceed a critical fibril length-scale of >100 nm. Our model enables the analysis of large-scale hierarchical amyloid plaques and presents a new approach to engineer the adhesive forces responsible of the self-assembly process of amyloid nanostructures. We conclude with a discussion of universal principles that hold for both graphene and protein based assembly into hierarchical structures, and outline opportunities for the design of mutable materials.
Biological materials often have a hierarchical structure which enables complex functionality. Biopolymers such as microtubules have monomers which are proteins that contain a rich variety of features incorporated into the basic building block. In development of materials that mimic aspects of natural systems, we will need to develop basic macromolecular building blocks that have a range of features. A promise of nanoscience is the creation of such complex nanoparticles, after all proteins are nanoparticles. We are working to understand the fundamental features of the monomers that will yield the geometry and dynamic properties of interest. In particular the focus of the modeling effort is determining design principles for assembly of tubular structures from monomers that mimic microtubules formed from the protein tubulin. We will discuss the results of simulations that show our monomer models can self-assembled into tubular structures including helical geoemetry without a chiral character in the monomeric building block. The role of the interactions in the dynamic assembly is critical in the assembly process with respect to defect tolerance. We will present a structure diagram of the different structures that form as a function of the interaction parameters.
We investigate the self-assembly of polydisperse inorganic nanoparticles (CdSe, CdS, ZnSe and PbS) into highly uniform supraparticles with a core-shell morphology. The self-assembly process is believed to be self-limiting due to the balance between van der Waals attraction and Coulombic repulsion as observed in experiments and further elaborated by our simulations. The uniform supraparticles are shown to be stable for a wide range of density rather than kinetically trapped. Our results further reveal that the remarkable nanoparticle polydispersity leads to the core-shell morphology of the supraparticles. The generic nature of the governing interactions suggests great versatility in the composition, size and shape of the constituent building blocks, and allows for a large family of self-assembled structures, including colloidal crystals.
Molecularly directed nucleation and self-assembly is a fundamental mechanism in biology to control the structure and property of biomaterilas and biominerals. In this paper, by using a combination of theoretical and experimental approaches, we demonstrate that functionalized graphene sheets (FGS) can be used as a new class of molecular templates to direct the nucleation and self-assembly and produce bulk, three-dimensional nanocomposite materials. We show that the interfacial energy controls the crystalline phase, as well as the nucleation and nucleation density. We further demonstrate that the FGS molecular templates can control the kinetics of complex 3D architectures. The electrochemical properties of the new materials are investigated for energy storage (batteries) and conversion (fuel cell) applications.
Focused studies of one-dimensional carbon nanotubes (CNTs) and two dimensional graphene are driven by their wide-ranging potential applications. However, utilizing the often-extraordinary physical and chemical properties in macroscale systems remains a real bottleneck to generalized application. There is a real need to develop practical technologies for transforming the as-produced CNTs and graphene  into materials or integrated assemblies with properties that are both fundamentally interesting and useful for applications. A novel method for tailoring the properties of nanocomposites by controlling the way in which nanomaterials are ordered, using colloidally derived polymer latex crystals is described. This simple colloidal deposition process facilitates the formation of highly ordered multi-arrays of polymer particles, which act as a template for the assembly of CNTs into three-dimensional hexagonal patterns and thus creates the possibility to overcome problems with filler distribution. The individual particles deform into rhombic dodecahedra, which is mainly driven by capillary forces as the system dries. Nanotubes are assembled and positioned at interstitial sites between the polymer particles resulting in a honeycomb-like arrangement. The use of this facile and elegant technology allows for the formation of robust mechanical composites with electrical percolations markedly lower than witnessed in more conventional polymer composites. The resulting composites maintain their electrical properties but can undergo large strain before failure. More surprisingly, when the stress is released the sample return to its original shape before deformation, while maintaining the inherent structural arrangement of nanotubes at interstitial points. The templated assembly of CNTs using plasticized colloidal crystals as described here can ultimately be generic for assembling a range of other low-dimensional nanostructures. Moreover, combining our surfactant-assisted-plasticization method with other controllable parameters, such as polymer-particle size and polymer type, should provide excellent control over structureâ?"property relationships for specific applications. In particular such highly ordered assemblies are expected to find applications in optical technologies.  Y. Hernandez, et.al. Nat. Nanotechnol. 2008, 3, 563.  Jurewicz et.al, Macromol. Rap. Comm. 2010, 31, 585  Jurewicz et.al, J Phys Chem B. 2011, 115, 6395  Worajittiphon et.al, Adv. Mater. 2010, 22, 5310
Porous Coordination Polymers (PCP), with their ordered nanoporous system and large surface area are very attractive for numerous applications, which involve controlled molecular transport properties. To fully exploit their potential, a straightforward processing method to deposit the PCP crystals on various substrates and to create freestanding membranes with controlled pore orientation is highly desirable. Here we report a strategy to self-assemble PCP crystals into two-dimensional monolayers using Langmuir Blodgettry. This approach allows the deposition on various substrates over several square centimeters, uniformly and with controllable density of the crystals. Additionally we show that by controlling the morphology of the crystalline building block we can program their orientation on the substrates. By using a copper grid as substrate these assemblies can also be fabricated as freestanding sheets. This approach represents a very simple and scalable processing method to translate the orientation of the channel network from the individual crystal to the macroscopic scale and can help to incorporate this interesting class of materials within advanced hierarchical systems.
Controlling the growth of inorganic materials on organic templates poses many challenges, but also opens vast opportunities for materials design. One of the important and yet unresolved questions is how does mineral growth affect the template structure. We present the theoretical study of titania nanoparticle nucleation and growth on functionalized graphene surfaces and on surfactant templates supported on graphene surface. We show that graphene functionalization, which modifies its interfacial chemistry, determines polymorph selection for nucleating titania nanoclusters. During the growth process on surfactant templates titania nanocrystals are initially confined between surfactant hemicylindrical micelles until they reach a critical size. Subsequent growth leads to at first partial and then complete rearrangement of the template structure to a monolayer configuration, which changes the mechanism of nanoparticle growth from predominantly thermodynamic to predominantly kinetic. The critical nanoparticle size can be controlled by controlling the stability of surfactant template with symmetric and asymmetric electrolytes. These results pave the way for designing synthesis pathways for nanocomposite materials with well-defined architectures.
The pattern of periodical poly(methyl methacrylate) (PMMA) stripes, covered with gold thin film, was fabricated via controlled evaporative self-assembly combined with ion sputtering. An intriguing two-stage wrinkling (thermal expansion-induced wrinkles and mechanically-driven wrinkles), as well as complex wrinkling instability patterns, were observed, due to the different mechanical properties of two regions (Au only and Au/PMMA bilayer). The nanomechanical properties of the composite structure were also investigated based on the buckling instability method.
Synthetic interconnected nanofluidic networks formed from a simple cooperative interaction between phospholipid vesicles and motor protein-based transport have been fabricated on the millimeter scale. These lipid networks possess inherent redundancies useful for high-fidelity materials transport via lipid surface fluidity or contained flow within the continuous connected tubules. The synthetic networks highly resemble the interconnected and reticulated lipid structures of the endoplasmic reticulum found throughout the cytosol. While these natural structures provide a matrix for organizing membrane constituents, the lumen (i.e. interstitial space) represents a continuous nanofluidic network for the transport of proteins and small molecules throughout the cell. Additionally, we create structures which mimic biological membrane (or tunneling) nanotubule connections, commonly used for intercellular signaling and transport(1). In our system, the energy-driven motility of microtubule filaments by surface bound kinesin motors provides an extracting force on the membranes of multilamellar liposomes, connected to the microtubules by biotin-streptavidin bonds, and results in the formation of highly bifurcated networks of lipid nanotubules. Because microtubules can translocate over a large two-dimensional surface in this inverted style assay, the total nanofluidic network size is only limited by microtubule trajectories, microtubule surface density, molecular motor energy source (ATP) and total amount and physical properties of the source liposomes. These parameters were varied systematically to tune the frequency of network bifurcation to increase or decrease the network redundancy. The system can thus accommodate critical failures between junctions without affecting material transport and separation. Additionally, we show that while nanoparticles bound to the surface of the nanotubes undergo diffusive transport that closely follows a 1D process, the application of external stimuli can concentrate and separate nanoparticles in a directed fashion. Overall, this incredibly flexible system can be used to help elucidate properties of the relatively complex transport and communication processes seen in vivo and additionally, can be used as an â?oon-chipâ? platform for materials capture and transport. * Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. 1. Rustom, A., Saffrich, R., Markovic, I., Walther, P. & Gerdes, H.-H. Nanotubular highways for intercellular organelle transport. Science (New York, N.Y.) 303, 1007-10 (2004).
Assembly of anisotropic particles into useful structures holds great potential for applications in photonics, electronics, optical and biological sensing. In most cases, however, these new building blocks may not naturally assemble into any desired structures. It is crucial to find a way that allows unprecedented control over the interaction force exerted on every individual particle. Such a technique for directed particle assembly is under development through application of external stresses such as electric field, magnetic field, and variety of templating approaches. Bimetallic Janus Particles (BJPs), composed of colloidal particles coated with differing metals on opposite hemispheres, have been our focus due to their unique properties. In particular, surface modification leads to a wide selection library of Janus particles with high tunability in conductivity, band gap, refractive index, etc. Previous work showed a solution based specific assembly of BJPs into periodic arrays of chain structures. However, the formed chain structure arrays were not stable during the process of phase transition. In this work, we will demonstrate a new approach to retain the resulting chain structures, which allows controlling the density and orientation of the assembled structures for future optical behavior demonstration.
Large-area films of vertically-aligned semiconductor nanorods are potentially useful as active materials in optoelectronic devices. We have demonstrated highly facile approaches to reversibly assembly CdSe nanorods into ordered, aligned arrays in solution. The preferential evaporation of a "good" solvent from a binary solvent mixture resulted in a continuous decrease in solvent quality and induced nanorod assembly by solvophobic interactions. A similar effect was achieved by cooling down a nanorod suspension from elevated temperature in a marginal solvent. The self-assembled structures consisted of free-floating sheets up to 24 Î¼m in diameter of hexagonally close-packed nanorods and were believed to form by a nucleation and growth mechanism. These platelets could be directly drop-cast from solution onto a substrate and rapidly dried to obtain a large-area film of vertically aligned nanorods. This assembly method was robust and effective over a wide range of solvents and nanorod concentrations with no need for applied electric fields, extensive control of drying conditions, exceptionally monodisperse nanorods, or high concentrations of additives. Modulating inter-particle interactions in this manner may also be useful for assembling other nanorod or nanoparticle systems.
Bottom-up fabrication of hierarchal structures made from nano- and micro-scale building blocks is sought for many applications including plasmonics, photonics, and phononics. In particular, discrete clusters of metal nanoparticles have been used as fano resonant biosensors; however, the fabrication process typically involves e-beam lithography which is time-consuming and limited to planar shapes. We herein demonstrate a methodology to create large scale patterns of islands of self-assembled particles from droplets confined on patterned microposts. We investigated different methods of breaking macroscopic droplets into femto-litre droplets of water-based suspensions of polymer and metal spheres. We use templated substrates with physical templates composed of either negative recesses, or positive features to deterministically control placement of the assembled particle clusters. Also, we tailor the surface energy of the top surface of raised features (posts) to become more hydrophilic in order to promote the entrapment of sessile droplets during a roll-to-roll compatible blade casting process. We measure the statistical distribution of cluster sizes on identical post arrays, and study the effect of the post geometry, inter-post spacings, and surface treatment on the resulting droplet size and number of particles per cluster. The high degree of control on uniformity as well as the deterministic nature of this approach is promising for scalable fabrication of plasmonic sensors.
Porous carbon has been widely used as electrode materials in energy storage applications due to its high surface area and high electronic conductivity. The lithium-sulfur (Li-S) battery has attracted great attention as a next-generation energy storage device, owing to its extremely high theoretical energy density. Several types of porous carbon materials have been proposed to synthesize carbon-sulfur nanocomposites to improve contact between sulfur and carbon and therefore the conductivity of the electrodes, leading to enhanced utilization of the active sulfur in Li-S batteries. This work will present synthesis and characterization of hierarchically structured porous carbon materials. Multiple building blocks including inorganic cluster, surfactant, and polymer spheres were used to direct self-assembly of carbon precursors into hierarchically structured porous carbon materials. The porous carbon materials are characterized by XRD, N2 sorption, TGA, SEM and TEM and possess high surface area, high pore volume and hierarchical pore structures. The carbon materials were further loaded with sulfur to generate carbon-sulfur nanocomposites to be evaluated as cathode materials for Li-S batteries. The relationships between physical and chemical properties of the carbon materials (such as surface area, pore volume, surface functional group, and their distribution in the materials) and its electrochemical performance are correlated. The finding will provide insight on development of high performance electrode materials for advanced sulfur batteries.
Epitaxy, which is commonly used in semiconductor fabrication, refers to a layer by layer process in which a crystalline film is grown on a substrate. A unique aspect of epitaxial growth is that the filmâ?Ts crystalline structure is controlled by the lattice parameters of the underlying substrate. Epitaxial growth has been extensively studied and used in atomic systems. We have extended this process to the self assembly of nanoparticle hetereostructures. Utilizing nanoparticles and self assembly provides a number of benefits for the fundamental studies of epitaxial growth of complex heterostructures. The size ratio of the nanoparticles in the substrate and epitaxial layers was precisely tuned through colloidal synthesis and in turn the magnitude of the strain between the layers was controlled. The composition of the nanoparticles was varied allowing the growth mode to be controlled as a function of strength of the interparticle interactions. For example, the deposition of gold nanoparticles on the lead sulfide nanoparticle monolayers resulted in Stranksi-Krastanov (layer then island) growth while the assembly of iron oxide nanoparticles followed the Frank-van der Merwe (layer by layer) model. Additionally, the large size of the nanoparticles, compared to atoms, allowed the individual position of nanoparticles to be easily tracked enabling strain analysis through image processing techniques. We will show how the extension of epitaxial growth to self-assembled nanoparticles provides a model system with precise tunability of the lattice parameters through control of the nanoparticle size and composition, and discuss its use in the design of functional materials through the proper choice of technologically important nanoparticles in the different layers.
Recently we published the synthesis of new hybrid materials, Ionic Silica Nanoparticle Networks (ISNN), made of silica nanoparticles covalently connected by organic bridging ligands containing imidazolium units owing to a â?oclick chemistry-likeâ? reaction. The photoluminescence experiments performed on these ISNN hybrid materials showed an emission around 410 nm, whereas the used precursors are not luminescent. The quantum yields measured, up to 26%, are extremely promising for photoluminescence applications of the ISNN. Among other techniques small-angle X-ray scattering (SAXS) experiments were carried out to get a better picture of the network extension. The SAXS experiments revealed a clear short-range order in ISNN materials. This short-range order is dependent on the rigidity of the bridging ligand. Moreover the shift towards longer wavelengths of the luminescence emission maximum, obtained when varying the aromatic ring content of the bridging ligand, suggested the existence of strong Ï?-Ï? stacking in the hybrid material. Experiments revealed a stronger luminescence in those samples exhibiting the higher extent of short-range order in SAXS. Thus the ordering of the hybrid material seems to be directly linked to the photoluminescence features of the material.
As the future of computing heads to super hand held â?oall in oneâ? devices like iPads, new novel switching and memory devices are needed that maintain a low power consumption with the computing capability the consumer demands. Nanotechnology will play a vital role in achieving this goal. Transistors based on the strain field of buried SiGe islands, and ordered Ge quantum dots (QDs) are proposed in literature for use as building blocks for quantum computing and memory devices. For such applications however, it is necessary to pre-define the location of the nanostructures precisely. Current fabrication methods provide random nucleation sites of the QDs. However, due to weak size-dependence of the total energy and kinetic effects such as coarsening, a rather broad size distribution of the QDs is observed. New methods for introducing ordered QDs and the desired size distribution are required. QDs are especially challenging due to their size and the required quality of the interfaces with the surrounding matrix material. The lattice mismatch of 4.2% between Si and Ge makes Ge nano-structures intrinsically strained. Strained layer growth allows for the formation of self-organized nanostructures via the Stranskiâ?"Krastanow (SK) growth when the film breaks up into three-dimensional islands. While SK growth is a simple bottom-up approach for the fabrication of nanostructures and QDs, current abilities of Si technology, especially the damage induced by reactive ion etching, are often inadequate. It is therefore of high importance to employ self-organization schemes in combination with pre-defined nucleation sites in the substrate for more accurate Ge QD-device fabrication. In the current work, a novel approach is proposed to pre-define the nucleation sites for the Ge QDs. First, a 20 nm SiO2 is grown on a Si wafer. Nanoindentation is used to define a matrix where the Ge QDs are expected to reside. AFM, Transmission and Scanning Electron Microscopy (TEM, SEM) are used to characterize the nano-patterned oxide/substrate. The results show 20 nm spacing between two sites. After that, a 10 nm Ge layer is grown using physical vapor deposition (PVD) sputtering on top of the nano-patterned oxide. During and after the growth, thermal heating is employed to start the QDs self-assembly process. AFM, TEM, and SEM are used to identify and characterize the growth of Ge QDs inside the nanoindentation sites. The QDs growth is expected to take place in the pre-defined nucleation sites, with the sizes of the QDs ranging between 10-20 nm in diameter. In addition, conductive AFM is used to characterize the Ge QDs electrical properties while scanning Kelvin probe microscopy is used to characterize the electrostatic properties.
In the continued effort towards the development of more lucrative alternative energy systems, materials with mutually exclusive sets of properties must be optimized. For example, the requirement of efficient charge transfer and high electron mobility in solar materials as well as the low thermal conductivity and high electrical conductivity needed in thermoelectric materials present challenges to the development of materials for these applications. Single crystal composite materials embody the potential to minimize the trade offs present in these systems. Synthesis models for single crystal composite materials abound in Nature and include mineral growth in a hydrogel-like environment to form single crystal macrostructures with complex architectures on the nanoscale. In this model, composite formation is achieved by incorporation of the gel-like matrix components during crystal growth without disruption to the translational periodicity of the lattice. In transferring this biomineralization-based crystal growth model to technologically relevant systems, the challenge is to identify the appropriate crystalline materials that are able to serve as hosts to accommodate guest matrix species without disruption to their single crystal character. In this work, crystal growth in hydrogels is used as a synthesis method to form single crystal composites based on oxide semiconductor materials (e.g., ZnO) with incorporated hydrogel media. The considerations of crystal growth rate and density of the hydrogel matrix are used as synthesis variables to allow the control of matrix incorporation as well as crystal morphology. X-ray diffraction studies and electron and optical microscopies will be used to probe both the crystalline nature of the oxide material as well as the effect of matrix incorporation on the nanostructure and microstructure of the composite products.
We used molecular dynamics simulations to study the self-assembly of artificial microtubules from model wedge-shaped monomers with bonding sites on their surfaces. The strengths of the bonding interactions required for the tube formation are found to be consistent with the predictions of a simple lattice model of polymerization. Our results indicate that tubes are only formed in a narrow range of bonding strengths. Interestingly, helical tubes and other helical structures are frequently observed despite the fact that such symmetry breaking is not inherent in the geometry and mutual interactions of wedges. Besides studying the self-assembly starting from a system comprised only of monomers, we also have simulated systems containing preformed tubes. In these simulations we observe the merger of tubes into longer ones, consistent with recent experimental results on the fusion of stabilized microtubules.
Many applications of block copolymer thin films require post-deposition annealing to allow the block copolymer to self-assemble and reduce defect density. Thermal annealing is an established technique for allowing block copolymers to self-assemble, while solvent annealing is a newer technique that offers several advantages over thermal annealing including room-temperature processing, control over the microstructure orientation and surface wetting, and the ability to anneal block copolymers not amenable to thermal annealing. We have developed a controlled process design for performing solvent annealing that incorporates continuous flows of solvent-saturated carrier gas, multiple simultaneous co-solvents, and in-situ metrology. This method is modular and applicable to a wide variety of block copolymer/solvent systems. Compared to existing techniques this general approach allows for greater reproducibility, stability, and control over the relevant solvent annealing process parameters. This improved control allows us to investigate in detail the effects of annealing and quenching conditions on the morphology of cylinder-forming polystyrene-b-polyethylene oxide (PS-b-PEO) thin films annealed at ambient temperature in an atmosphere with controlled saturations of toluene and water solvent vapors. Examining the annealed films by atomic force microscopy (AFM), we find that the quenching conditions are crucial to achieving the desired microstructural orientation; if the water vapor saturation of the quenching gas flow is below a critical level the final morphology consists of PEO cylinders oriented parallel to the substrate, while above the threshold the cylinders are hexagonally packed and oriented perpendicular to the substrate. We are also able to tune the PEO domain spacing in films displaying perpendicularly-oriented cylinders over a wide range solely by controlling the saturation of water vapor during the annealing process. This new approach to solvent annealing provides control over the relevant solvent annealing process parameters and allows a fundamental understanding of the block copolymer self-assembly process to be developed, making solvent annealing more relevant to industrial applications.
A novel procedure for fabricating nanochannel arrays and networks in PDMS with length:width:height aspect ratios of 1000:1:1 or greater is presented. The nanochannels were created using a templating process from gold nanowire arrays that were previously fabricated on glass substrates by the process of Lithographically Patterned Nanowire Electrodeposition (LPNE). The gold nanowire widths and heights were independently adjusted and each ranged as small as 50 nm; the gold nanowires created by LPNE can be up to centimeters in length. A thin-layer special blend of PDMS was used to cast and create nanochannels from the gold nanowires with sub 100 nm x 100 nm cross-sections, and lengths up to 1 cm. The dimensions and integrity of the nanochannels were characterized by a combination of AFM, SEM and fluorescence measurements. The nanochannel networks created by this nanowire templating process are fully tunable and can assume complex shapes as defined by the initial lithography. SU-8 structures were patterned onto portions of the nanowire network to form an overall master mold that could be easily integrated into conventional PDMS based microfluidics. This nanochannel fabrication procedure offers a simple and rapid method for obtaining sub 100 nm, high aspect ratio nanofluidics using only parallel processes (no direct writing methods are needed). The initial application of these nanoparticle networks is for the electrophoretic separation of nanoparticles.
In recent studies, we have used resonance Raman spectroscopy and scanning probe microscopy to uncover the surprising internal structure of the self-assembled aggregate of tetrakis(4-sulfonatophenyl)porphyrin (TSPP). Results have been interpreted in terms of strongly-coupled 6-nm diameter circular aggregates (cyclic N-mers) of the diacid form of TSPP, which further assemble into large helical nanotubes, approximately 20 nm in diameter with a shell thickness of 2 nm. The result is a red-shifted (J-band) transition of the aggregate that is split into longitudinally and transversely polarized excitonic states. The cyclic N-mers, reminiscent of the light-harvesting complexes of purple photosynthetic bacteria, are held together by electrostatic forces and serve as the basic unit for a calculation of the spectroscopic transitions of the aggregate. A key aspect of our model is that nonplanar distortions of the protonated porphyin drive assembly into circular aggregates. These are further perturbed by water-mediated hydrogen bonding forces that are responsible for assembly of the cyclic N-mers into helical nanotubes, permitting proton-mediated excitonic coupling among the hierarchal sub-units. In the present work, an excitonic calculation of the lineshapes of both the red-shifted (J-band) and blue-shifted (H-band) components of the TSPP Soret band is presented, including the effects of effective Franck-Condon active vibrational modes. The results shed light on the site shifts of the porphyrin in the aggregate and the difference in coupling strength for the H- and J-bands. We present evidence that aggregation leads to further nonplanar distortions of the porphyrin beyond those which accompany protonation of the monomer.
We demonstrated the formation of hierarchically porous carbons by double templating process. Specifically, self-assembled polymeric colloidal crystals were applied as a template for macropores and block-copolymers were used to introduce mesopore structure. The macroporous structure could be conveniently controlled with adjusting pore sizes of hard template. The mesopores could have hexagonal, body-centered cubic and lamellar structure by different block-copolymers and tuning the concentration of the copolymer surfactants. By referring metal catalyst, the crystallinity of the carbon could be increased. The structural and morphologic properties of different carbon materials were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Brunauer-Emmet-Teller (BET) analyses and electrochemical property was analyzed by cyclic voltammetry. These carbon materials have large surface area and good electron conductivity. They were applied as a counter electrode of dye-sensitized solar cells (DSSCs). The conversion efficiency of DSSCs with these carbon-coated counter electrode reached 95% comparing with Pt coated DSSCs.
Fabrication of nanoscale patterns through the bottom-up approach of self-assembly of phase-separated block copolymers with a high degree of registry and regularity on the nanoscale of 10-100 nm with importance to high performance microelectronics applications at dimensions and densities inaccessible to traditional lithography methods . However, self-assembled constructs to develop nano-circuitry on the macroscopic scale remains distant but combination of lithography and self-assembly might be used for sub-20 nm feature sizes. Nanostructure templates fabrication from P(S-b-MMA) thin films requires precise control of interfacial energies to achieve perpendicular orientation of microdomains to the substrate surface. Neutralized surfaces, i.e., surfaces exhibiting equal interaction energies with PS and PMMA, can be obtained by modifying the oxide layer on silicon with a covalently anchored hydroxyl-terminated random copolymer P(S-r-MMA) termed a â?oneutral brushâ? . This commonly employed method enables precise fine-tuning of interfacial energies, but involves a lengthy process, requires starting materials that are commercially available but expensive, and results in a relatively thick under layer that can interfere with subsequent surface processing. We report here the microphase separation behaviour of symmetric and asymmetric P(S-b-MMA) diblock copolymers on electronic substrates modified with ethylene glycol (EG) self-assembled monolayer (SAM) as alternative to standard random copolymer brush. The diblock copolymer films deposited on EG SAMs upon thermal annealing spontaneously generates features with sub-lithographic resolution and pitch with perpendicular orientation. Selective etching provides a rapid route for the generation of PS template structures as the PMMA domains are etched at a faster rate. These templates can subsequently be used as etch masks to generate nanoscale features. We use state of the art lithography to generate sub-Î¼m features and within these generate nm sized copolymer templates. Graphoepitaxy method proved a successful approach for the alignment of the microphase separated structures. TEM cross-section analysis reveals the transfer of the template deep in to the underlying silicon. This method of EG SAM driven self-assembly provides a simple, rapid, yet tuneable approach for surface neutralization. The results demonstrate an exciting nanofabrication technique for creating high density nanoscale features for the nanoelectronic industry. References:  R A Farrell, T G Fitzgerald, D Borah, J D Holmes and M A Morris. Int. J. Mol. Sci. 10 (2009) 3671.  D Borah, M T Shaw, S Rasappa, R A Farrell, C Oâ?TMahony, C M Faulkner, M Bosea, P Gleeson, J D Holmes and M A Morris. J. Phys. D: Appl. Phys. 44 (2011) 174012. Acknowledgement: This work is supported by EU FP7 LAMAND (245565) project and CRANN, Ireland.
This paper describes our recent research using a range of MOFs imbedded within the channels of a microfluidic device for precisely controlling separations on an exceptionally small scale. Interest in the junction of these two areas of research arises from the desire to enhance product separations after a reaction is complete on a single lab-on-a-chip (LOC) device. Microfluidics concerns the control and manipulation of fluids on the micron-scale typically within enclosed channel structures that have diameters ranging from 10-500 microns. The movement of fluids under microfluidic conditions is generally characterised by laminar flow which results in consistent and predictable mixing regimes. For this reason, microfluidics has found applications in chemistry and biology ranging from micro-scale chemical reactions to DNA analysis and cell culture. Metal-organic frameworks (MOFs) consist of metals or a cluster of metals supported by multidentate organic bridging ligands to create stable porous crystalline solids. These structures can be a one-dimensional chain, a two-dimensional sheet or a three-dimensional crystal network. A range of applications for MOFs have been suggested and tested in the literature including hydrogen gas storage, gas purification, gas separation and catalysis. The potential for MOFs to be used for separation of both gases and solution mixtures has been appreciated for some time. One recent proof of concept study displayed chromatographic separations of two different dye molecules using a single MOF-5 crystal on a dye saturated gel(1). In this paper MOF-5, HKUST-1 and a series of Zn(II) MOF (complete with silicon containing linkers)(2) have been studied for the ability to separate a range different compounds after initial mixing in a microfluidic LOC device. It is shown that the dye molecules diffuse through the MOF scaffold at different rates depending on their molecular size in comparison to the size of the MOF pore. (1)Han, S.; Wei, Y.; Valente, C.; Lagzi, I.; Gassensmith, J. J.; Coskun, A.; Stoddart, J. F.; Grzybowski, B. A. J. Am. Chem. Soc. 2010, 132, 16358â?"16361. (2)Davies, R. P.; Less, R. J.; Lickiss, P. D.; Robertson, K.; White, A. J. P. Inorg. Chem. 2008, 47, 9958-9964.
Bottom-up design of materials via self-assembly of appropriate building blocks offers the possibility of developing innovative three-dimensional materials with new functionalities. Helical optically active biocompatible poly(3-methyl-4-vinylpyridine)/(R) and (S) mandelic acid complexes have been prepared. A diblock copolymer of helical poly[(3-methyl-4-vinylprydine)/mandelic acid complex]-block-poly(styrene) has been processed into smectic layer-like helical-bundle structures on silicon wafer. Additionally, optically active helical poly(2-methoxystyrene) (P2MS) has been synthesized and the surfaces of the chiral helical P2MS have been shown to be effective as supports for mouse and human osteoblast cells. The cell attachment and growth data demonstrate that the chiral P2MS surfaces were better supports compared to achiral P2MS surface. Furthermore, biocompatible optically active helical poly(2-methoxystyrene)-block-poly(ethylene oxide) diblock copolymers have been synthesized. These block copolymers can be processed into helical superstructures. The synthesis of the helical polymers and diblock copolymers (containing a helical block), biofunctional properties and the processing of the diblock copolymers into superstructures will be presented.
We have developed a microfluidic system for the fabrication of shaped polymer microfibers which takes advantage of hydrodynamic forces to control both molecular orientation and fiber cross-sectional shape. This system combines hydrodynamic focusing with passive groove structures integrated into the channel walls to generate a sheath flow of a pre-polymer material of varying cross-sectional size and shape. Shear forces and the utilization of a liquid crystal component provide mechanisms for orienting the molecular structure of the polymer fiber, while the design of appropriately shaped grooves in the channel walls generate hydrodynamic forces which direct fiber shape. Downstream of the grooves the fiber material is photopolymerized within the microfluidic channel and subsequently extruded for collection and characterization. A primary motivation of this work is to investigate the potential effect of fiber cross-sectional shape on bulk material properties of a composite. For example, fibers which have hooked features may be able to interlock with each other while flat, ribbon-shaped fibers may be stackable into brick-and-mortar type structures. Such novel physical mechanisms may provide an entirely new route for increasing the lateral strength or stiffness of fiber-based composites. In addition, the increased surface area of non-round fibers may make such structures desirable for applications such as controlled-release materials and tissue engineering scaffolds.
Porous coordination polymers (PCPs), assembled by metal ions and organic bridging ligands, are an intriguing class of crystalline porous materials, as it is possible to design their framework topologies and pore sizes and the functionality of the pore surfaces. On the other hand, functionalization of PCP other surfaces (crystal surfaces) is a great challenge, but it is a promising methodology not only for modification of the porous properties but also for the addition of a new function to the PCP without changing the characteristic features of the PCP crystal itself, resulting in the fabrication of multifunctional PCPs. One way to decorate the crystal surfaces of a PCP is to hybridize the core PCP crystal with a different shell crystal by epitaxial growth at the single-crystal level, thus creating core-shell PCP heteroepitaxial crystals. Such a lattice match promises pore connections at the interface between crystals. We demonstrated the synthesis of hybridized PCP single crystals by taking the advantage of coordination equilibrium at the crystal interfaces and determined the structural relationship between the shell and the core by using surface X-ray diffraction analysis. Furthermore, we demonstrated the integration of size selectivity with high storage based on this concept.
Top-down synthesis by downscaling traditional materials has been a main strategy for the development of nanomaterials, which has driven revolutions in various areas such as composites, MEMs, tissue engineering and so on. Successful examples include producing graphene from graphite, cellulose nanofibers from cotton or silicon nanostructures through bulk silicon, whose implementation always open new research opportunities. Kevlar, the strongest textile material, have received scarce attentions on the synthesis and applications of its nano forms. It is really surprising since other organic nanofibers, such as cellulose, have sophisticated investigation and demonstrate applications in various areas by exploiting its solution, mechanical and biocompatible properties. In this talk, I will demonstrate that successful exfoliation of high-aspect ratio Kevlar nanofibers can be achieved through deprotonation of molecular chain in Kevlar microfibers. The disruption of the chain architecture leads to the weakening of hydrogen-bonding interactions, which facilitates the disassembly of microfibers into nanofibers in the medium of organic solvent. The stable nanofiber dispersions can be further transformed into gel through a solvent exchange process, in which water is made to slowly diffuse into the nanofiber dispersions. The reprotonation of nanofibers leads to phase separation but the network of nanofibers can be well maintained by the concomitant restoration of hydrogen bonds. The hydrogel formation process can be easily tailored to make highly porous inverted colloidal crystals, which can have potential applications in tissue engineering. In addition, various nanoparticles, such as ZnO nanorods or magnetic sheets can be grown inside the gel to improve its strength and multifunctionality.
DNA micro- and nano-arrays are powerful platforms for the study of protein/DNA interactions, gene sequencing, and clinical point-of-care diagnostics. We have developed a simple strategy for the high throughput fabrication of nanostructured surfaces and the hierarchical assembly of DNA arrays at these surfaces. Our platform possesses the following important advantages: high throughput fabrication via simple process flow, precise nanostructure positioning and uniformity, low non-specific adsorption, and nearly ideal specificity/fidelity. These advantages have enabled us to monitor biomolecular interactions at both the single-molecular and small ensemble levels. Our findings hold significance for the construction of functional DNA-modified architectures.
We present a method for the assembly of high-aspect ratio microcrystals using magnetic fields. This process is a step towards taking the fabrication of ordered array solar cells â?oout of the cleanroomâ?, in order to lower costs sufficiently to enable mass production. This allows batch-scale solution-phase processes for the synthesis of the nano- or microscale semiconductor active materials to be leveraged, by taking advantage of directed assembly to order the crystals into a usable array. Self- and directed assembly are well-understood at the nanoscale, but kinetic restraints that scale with size have limited most investigations at the microscale to low-aspect ratio structures. Magnetic alignment addresses this problem and enables the assembly of microwires with lengths of 100 microns and aspect ratios as high as 50. Ferromagnetic Ni coatings were applied to Si microwires using solution phase deposition, where the thickness and roughness of the coating can be controlled to tune the magnetic responsivity of the microwires. The Ni-coated microwires, randomly dispersed on a substrate, were vertically-aligned in a magnetic field, as the magnetic torque causes the wires to orient perpendicular to the substrate. The response of magnetically-functionalized wires is proportional to the thickness of the ferromagnetic coating, such that thicker coatings led to a higher population of perpendicularly-aligned wires. The lateral ordering of the wires was monitored in situ with optical microscopy, and X-ray diffraction was used to evaluate the degree of vertical alignment. Magnetically-assembled wire arrays with high degrees of alignment have been captured in polymer films for use as flexible active layers in solar devices.
Biological monomers such as peptides and proteins have an ability to form fibrils and nanotubes. Synthetic peptide monomers have also been shown to self-assemble into nanotubes, nanofibrils and hydrogels, based on their composition. For instance, the amyloid fibrils have been be mimicked using aromatic peptides. Plasma Enhanced Chemical Vapor Deposition (PECVD) has been utilized to deposit several aromatic dipeptides into thin films of nanofibrillar forests. Dipeptides were sublimed into a reactive plasma species using a home-built reactor and allowed to deposit onto downstream substrates. Specifically, diphenylalanine and dityrosine were examined in a pulsed PECVD reactor configuration. PECVD allows the sublimation of the peptide and deposition of a dense, uniform forest of nanotubes with a controlled thickness. Previously, the dipeptide nanotube self-assembly has been demonstrated in aqueous and organic solutions. These PECVD deposited nanostructures are reminiscent of the self-assembled structures from solution. At the molecular level, the peptide monomers can self-assemble into coiled structures (Î±-helices) or ordered crystalline structures (Î²-sheets). X-ray diffraction studies have confirmed the crystalline ordering of the peptide nanotubes. Such dipeptide-based nanotubes are stable in high temperatures up to 300 Î¿C and are very rigid, having high Youngâ?Ts modulus. The morphology of the peptide nanotubes was determined using LVSEM, TEM, and AFM as a function of various deposition conditions (power, frequency, flow-rate and deposition time). The nanotubes have a range of diameters from 50-300 nm and the length varies from 10 â?" 50 micron depending on the time of deposition. Such nanotubes of high aspect ratios can be useful for self-assembled nano-scale devices. Morphological differences between the two dipeptide nanostructures were observed with the dityrosine peptide exhibiting spherical nanowires while the diphenylalanine structures exhibiting faceted tubules. In addition, density differences through the thickness of the forests by controlling PECVD deposition parameters were also examined.
For 3.5 billion years, whenever microtubule was required to perform additional functions, eukaryotic cells supplied the essential molecule to tubulin, to absorb it inside any of its six locations and produce microtubule; -all original properties remained intact except the function added by the new molecule. Accurately preserving the parent properties even after structural transformation is contradictory to the fundamental concepts of materials science. Moreover, in nanotechnology, only a few number of atoms, could significantly change the properties of a material, while, all sizes of microtubules should have identical electronic and optical properties. By physics laws, condensates can alleviate size-effect, therefore, if microtubule is not a condensate, with the addition of new tubulins, all past information is changed or lost; consequently, evolution would stop abruptly. In addition, change in property with the addition of new molecule would stop cellular transport and all living creatures (eukaryotes) would die immediately. Here, we resolve the fundamental problem by experimentally proving that microtubule is a condensate. Using tubulin and embedded molecules from various living species, we have artificially produced their typical microtubules only by triggering the protein synchrony via modulation of the radio frequency exposure--converging billions of distinct functional forms of microtubules into a single synthetic-protocol. Our observation that proteins emit laser like signals while forming microtubule, assemble into a cylindrical shape even without GTP, exhibit identical electronic and optical properties for all lengths, and finally, squeeze millions of distinct atomic vibrations into a few when exposed to an intense laser, prove that microtubule belongs to a hitherto unknown class of bio-condensate. Following our protocol it would be possible to generate error free giant supramolecular architectures within a few microseconds by pumping a suitable radio wave.
Control over composition and structure across multiple nano- to macroscopic length scales remains a major grand challenge of synthetic materials science, entirely achievable, given the myriad of successes found in nature. For example, efforts to understand and mimic silica biomineralizationâ?"exemplified by diatom derived silicaâ?"are motivated by the possibility of designing similarly exquisite forms through self-assembly, but also towards the development of biocomposites and catalysts with increased stability and utility via silica stabilization. Silica skeletons from diatoms (frustules) have already found a number commercial applications as environmental sensors, filters, and scaffolds for shape preserving transformations to other functional materials. An ability to generate cell frustules from alternative sources such as mammalian cells would enable both natural and engineered cell heterogeneity to be exploited in the design of complex materials. Here we have realized a generalized route to synthesize biomorphic silica, analogous to diatom frustules, using mammalian cells as scaffolds directing complex structure formation. Inter- and intracellular heterogeneity from the nano- to macro-scale is captured and preserved in these composites following drying and high temperature processing allowing, for instance, shape preserving pyrolysis of cellular architectures to form conductive carbon replicas. The structural and behavioral malleability of the starting material (cultured cells) provides vast opportunities to develop robust and economical biocomposites with programmed structures and functions.
The programming of molecules for self-assembly typically targets the formation of nanostructures, monolayers and bilayers, liquid crystals, crystals, and biphasic patterns. In these systems the interplay of a set of molecular interactions and entropy generates ordered structures. There remains a grand challenge in designing structures with various types of order at different length scales that are hierarchical as observed in biological systems. This lecture discusses self-assembly pathways that combine electrostatic and short range interactions between charged small molecules and polyelectrolytes with other forces to drive the assembly of hierarchical structures. Three specific systems to be described include the formation of cell-like filamentous microcapsules formed by biopolymers and peptides, the assembly of a virus-like particle, and the assembly of catalytic systems. The potential functions of these systems will be described as well and include protein delivery to cells, transfection, and catalytic systems of interest for solar biofuel production.
The directed assembly of micellar and colloidal particles into 2D and 3D arrays has been a subject of study for a considerable time. Here we demonstrate the unique assembly properties of dynamic micellar nanoparticles by combining top down 2D and 3D lithographic nanopatterning techniques with solution-based bottom up self-assembly. The templates for the directed self-assembly of the micelles consisted of arrays of cylindrical recess features fabricated by nanoimprint lithography as well as 3D structures formed via interference lithography. The micelles were formed via the self-assembly of the block co-polymer polystyrene-b-poly(4-vinyl pyridine). The micelles were approximately 325nm in diameter in aqueous solutions (pH = 2.5) and 50nm in diameter in the dry state. The average number of micelles assembled per feature increased from less than 1 to 12 with increasing feature diameter in the range of 200nm-1micron. Using a 2D model for maximum packing of circles in circular host features, the effective sphere size of the micelles during assembly was calculated to be 250nm in diameter. In more complex structures, the complexity of the micellar assemblies also increased. This dramatic variation in nanoparticle volume during the assembly process offers unique opportunities for forming nanometer-scale, multidimensional arrays not accessible using hard sphere building blocks.
We synthesized Gold-Poly-N-isopropylacrylamide core-shell particles with single gold nanocrystal cores and homogeneous polymer shells. This synthetic routine allows us to obtain very low overall polydispersites (< 10%) . Due to the thermoresponsive behavior of Poly-N-isopropylacrylamide (PNIPAM), the volume of these colloids, and as a consequence the particle volume fraction, is a function of temperature. Hence, PNIPAM represents a responsive spacer between the individual nanocrystal cores . For the preparation of 2D and 3D assemblies such distance-control is of great importance for tuning the lattice constant. Here we show results on the preparation of millimetre-sized crystals with strong diffraction in the visible . The crystal structure was investigated by Small Angle Neutron Scattering. The measured scattering functions allow determination of the form factor P(q) and the structure factor of the assembly S(q). The presented core-shell particles crystallize in fcc structures. Crystallization was observed over a broad range of particle concentrations at (and below) room temperature. Upon an increase in temperature, the PNIPAM shells shrink and the overall particle volume fraction decreases, which causes melting of the crystals in a certain concentration range. Upon cooling, crystallization occurs again, once a critical volume fraction is reached. These melting/recrystallization processes were observed to occur with very high reproducibility as will be demonstrated in this contribution. This unique behaviour is interesting for applications in sensing and optics since it presents a new pathway towards the controlled preparation of large-scale â?~nanocrystal-dopedâ?T photonic crystals.  M. Karg, S. Jaber, T. Hellweg, P. Mulvaney, Langmuir 2011, 27, 820  S. Jaber, M. Karg, A. Morfa, P. Mulvaney, Phys. Chem. Chem. Phys. 2011, 13, 5576  M. Karg, T. Hellweg, P. Mulvaney, Adv. Funct. Mater. DOI: 10.1002/adfm.201101115
The field of layer-by-layer (LbL) assembled multilayer thin films has been active now for about twenty years. During this time, it has been established that essentially any material with suitable secondary bonding abilities, that can be dissolved or dispersed in aqueous solutions, can be assembled into multilayer constructs by using the layer-by-layer processing approach. This enormous versatility has allowed the creation and exploration of a wide range of functional thin film multilayer heterostructures with nanoscale controllable thicknesses, layered architectures and physical/chemical properties. Although the versatility of this process, in terms of both the types of materials that can be manipulated and the manner by which they are manipulated, is enormous, there still remain many unresolved and largely unexplored fundamental and technological issues that, if solved, could result in new technological opportunities. In this talk, a variety of technical challenges and opportunities will be discussed. These will include, the LbL assembly of polymers and nanoparticles in nanoscale confined geometries, the use of living cells as functional elements in LbL assembled films and the hydrogen bonding assembly of poly(vinyl alcohol).
Directed nanoparticle (NP) assembly is of great interest in order to achieve desired NP structures for various application purposes. In this presentation, we will present our recent results on employing polymer crystallization (PSC) to direct NP assembly. Three types of hierarchically ordered hybrid materials will be discussed. First, tailor-made, free-standing NP frames and wires containing single or multiple types of NPs have been obtained by using an in-situ polymer crystallization method. End functionalized poly(ethylene oxide) single crystals were used as the templates. Gold and magnetite NPs were successfully patterned as evidenced by transmission electron microscopy experiments. Secondly, carbon nanotube induced polymer crystallization were used to guide AuNPs to assemble into periodic pattern with controlled periodicity. Thirdly, polymer nanofibers decorated with block copolymer single crystals were used as templates to induce the formation of hydroxyapatite (HA) nanocrystals and the resultant nanofiber/HA hybrids mimic the structure of natural bones.
In nature, the formation of complex morphologies is often driven by morphogenetic fields which originate from the formation and diffusion of chemical compounds that induce specific cellular responses. This concept has been mimed to obtain morphogen driven film buildup. The assemblies were self-constructed through the Huisgen-Sharpless Cu(I) catalyzed click-reaction where an azide reacts with an alkyne under the presence of Cu(I) giving a triazole group. Cu(I) which plays the role of morphogen, is generated at an electrode by electrochemical reduction of the Cu(II) present in solution. These Cu(I) ions then diffuse from the electrode towards the solution and locally induce the click-reaction. This process was illustrated with a layer-by-layer buildup of polymeric films  and a first example of one pot morphogen driven assembly where all the building blocks are simultaneously present in solution . The integrity of these films relies on covalent triazole bonds formed between azide and alkyne bearing poly(acrylic) acids (PAA) in presence of Cu(I) ions. The evolution of the construction is followed through electrochemical quartz crystal microbalance technique (EC-QCM) which allows simultaneously performing electrochemical reactions and following the mass deposited on the electrode A generalization of this concept to films whose integrity relies exclusively on host-guest interactions is presented here . Alkyne functionalized ferrocene and Î²-cyclodextrin have been mixed with azide bearing PAA in presence of Cu(II). By bringing such a solution in contact with an electrode and applying a voltammetric cycle with a potential range from +750 mV to -350 mV, a continuous film buildup composed of the three components was achieved. The possibility of tuning the ratio of these compounds in the film is investigated. Alkyne bearing molecules are grafted in situ to PAA chains via click chemistry whereas reversible host-guest interactions between ferrocene and cyclodextrine groups link polymer chains together. This reversibility induces new properties to the final assembly such as electrodissolution or further functionalization. In the case where empty cyclodextrin groups were available in the film the ability of trapping and releasing hydrophobic molecules has been described. . Rydzek, G.; Thomann, J.S.; Ameur, N.B.; Jierry, L.; MÃ©sini, P.; Ponche, A.; Contal, C.; El Haitami, A.E.; Voegel, J.-C.; Senger, B.; Schaaf, P.; Frisch, B.; Boulmedais, F. Langmuir. 26, 2816-2824, 2010. . Rydzek, G.; Jierry,L; Parat, A.; Thomann, J.S.; Voegel, J.-C.; Senger, B.; HemmerlÃ©, J.; Ponche, A.; Frisch, B.; Schaaf, P.; Boulmedais, F. Angew. Chem. Int. Ed. 50, 4374â?"4377, 2011. . Rydzek, G.; Parat, A.; Polavarapu, P.; Baehr, C.; Voegel, J-C. ; HemmerlÃ©, J.; Senger, B.; Frisch, B.; Schaaf, P.; Jierry, L.; and Boulmedais, F. Soft matter, 2011, DOI : 10.1039/c1sm06254a
Hybrid mixed oxide materials, which contain organic and inorganic molecular components, can be engineered over a wide range of length scales to exhibit unique combinations of mechanical, thermal, and optical properties. Hybrid materials are therefore ideally suited to a bottom-up materials design where molecular structure and resulting properties can be engineered and tailored to achieve desired property sets. In this work, we e