While analyzing all available protein structures for the presence of knots and slipknots we detected a strict conservation of complex knotting patterns within and between several protein families despite their large sequence divergence [1]. Since protein folding pathways leading to knotted native protein structures are slower and less efficient than those leading to unknotted proteins with similar size and sequence, the strict conservation of the knotting pattern indicates an important physiological role of knots and slipknots in these proteins. Although little is known about the functional role of knots, recent studies have demonstrated a protein-stabilizing ability of knots and slipknots. Some of the conserved knotting patterns occur in proteins forming trans-membrane channels where the slipknot loop seems to strap together the trans-membrane helices forming the channel. 1. Conservation of complex knotting and slipknotting patterns in proteins, J. I. Sulkowska, E. J. Rawdon , K. C. Millett, J. N. Onuchic and A. Stasiak, Proc Natl. Acad. Sci. U S A. 2012 Jun 26;109(26):E1715-23.

Nature provides an impressive example of a photonic crystal based on chiral network-like structures, as the cubic so-called srs network or gyroid structure realized in wing scales of several butterfly species. Due to its spatial chirality it shows circular dichroism, that is, different transmission rates for left- and right-circularly polarized light [Saba et al, Phys Rev Lett, 106.103902, 2011], a finding that may be of relevance for insect communication in the near-ultra-violet wavelengths. Keeping this network as a basic building block, other chiral structures can be constructed by intergrowth of 2, 3, 4, 8 or more srs nets resulting in structures of different topology to the single srs net. We here demonstrate that the intergrowth of multiple networks leads to fundamental change in the photonic properties of the structures, some of which can be rationalised in terms of the topology change. Owing to recent advances in nanofabrication technology, network structures of the complexity of the Gyroid can now be fabricated on a length scale of microns; we demonstrate the construction of single and doubly intergrown srs nets by direct laser writing methods and measurements of their optical properties [Turner et al, Optics Express, 19, 10001, 2011].

Cellulose is the most common naturally occurring biopolymer. Irrespective of the source of cellulose, it is present as long thin microfibrils. The microfibrils are believed to comprise of elementary microfibrils which are further made by supra-molecular organisation of cellulose chains. The hierarchy and the dimensions at various hierarchical levels vary with the source of cellulose. Information at different length scales is required in order to understand the cellulose structural organisation and also the biosynthetic machinery involved in various organisms. Ever since the discovery of cellulose, a lot of work has been done to understand the supramolecular organisation and trace back the biosynthesis process and vice-versa. Here, measurements from various techniques like XRD, SAXS, AFM and SEM has been used to obtain information at different length scales and a model for the structural organisation in cellulose from various sources has been proposed. The crystallites, microfibrils of cellulose from bacterial and animal origin are compared and related to their biosynthesis machinery.

Teeth represent the most highly mineralized and hardest tissues in mammals including humans.[1, 2] Their extraordinary mechanical properties are due to a special hierarchical arrangement of the constituent carbonated calcium-deficient hydroxyapatite ("bioapatite") crystals.[3] As in mammalian teeth, the structural building elements in shark teeth occur in a hierarchical order: The outer part consists of hard and mineral-rich enameloid, whereas the inner part consists of softer and less mineralized dentin. In contrast to mammalian teeth, which consist of hydroxyapatite, Ca5(PO4)3(OH), shark teeth contain fluoroapatite, Ca5(PO4)3F, as biomineral phase.[4] The aim of our work was to correlate the hierarchical structure, composition, and excellent mechanical properties of shark teeth. The teeth of two recent shark species (Isurus oxyrinchus, shortfin mako shark; and Galeocerdo cuvier, tiger shark) and a geological fluoroapatite crystal were structurally and chemically characterized with a broad range of advanced analytical methods, including nanoindentation and high-resolution scanning electron microscopy. In contrast to dentin, enameloid showed sharp diffraction peaks which indicated a high crystallinity of the enameloid. The lattice parameters of enameloid were comparable to those of the geological fluoroapatite crystal. The inorganic part of shark teeth consisted of fluoroapatite with a fluoride content in the enameloid of 3.1 wt%, which is close to the fluoride content of the geological fluoroapatite crystal (3.64 wt%). Isurus oxyrinchus enameloid consists of hierarchically arranged bundles of thin and long fluoroapatite crystallites. The three-dimensional orientation of these bundles substantially influences the local mechanical properties and the fracture behavior. Thermogravimetry showed that dentin had a higher content of water, organic matrix, and carbonate than enameloid. Using ion-selective potentiometry, we found a higher percentage of fluoride in enameloid compared to dentin. Nanoindentation and Vicker&’s microhardness tests showed that enameloid of shark teeth was approximately six times harder than dentin. We showed that the different biological functions of the shark teeth (‘‘tearing&’&’ for Isurus oxyrinchus and ‘‘cutting&’&’ for Galeocerdo cuvier) are controlled by the different geometry and not by the chemical or crystallographic composition. In conclusion, the excellent mechanical properties of shark teeth can be attributed to its three-dimensional hierarchical structuring. Our findings may be used to design a novel bio-inspired material, based on shark teeth structure and composition. References: [1] S. V. Dorozhkin, M. Epple, Angew. Chem., Int. Ed. 2002, 41, 3130. [2] H. A. Lowenstam, S. Weiner, On biomineralization, Oxford University Press, New York, 1989. [3] J. W. C. Dunlop, P. Fratzl, Annu. Rev. Mater. Res. 2010, 40, 1. [4] J. Enax, O. Prymak, D. Raabe, M. Epple, J. Struct. Biol. 2012, 178, 290.

Giant vesicles have sizes in the range of ten to hundred micrometers, which defines their unique property: they are visible under a light microscope. These systems provide a handy biomimetic tool for displaying the membrane morphology on the cell-size scale and its response to external perturbations. This talk will discuss vesicle deformation caused by electric fields as well as curvature response of the membrane in the presence of various molecules in the bathing medium. Particular emphasis will be given to vesicles loaded with polymer solutions. The interior of living cells is crowded with macromolecules. In such a concentrated environment, local phase separation may occur, involving local composition differences and microcompartmentation. Recently, giant vesicles loaded with polymer solutions were reported to exhibit spatial compartments formed by phase separation within the vesicle. We employed these artificial cell systems to study various phenomena related to molecular crowding and microcompartmentation in cells. We demonstrate that similarly to the wetting behavior of liquid droplets in contact with surfaces, different polymer aqueous phases in contact with membranes as a substrate can undergo complete to partial wetting transition (Y. Li, R. Lipowsky and R. Dimova, J. Am. Chem. Soc. 130:12252, 2008). We find that the degree of wetting is characterized by a hidden material parameter - the intrinsic contact angle, which can be determined from effective contact angles observed by optical microscopy (H. Kusumaatmaja, Y. Li, R. Dimova, and R. Lipowsky, Phys. Rev. Lett. 103:238103, 2009). Upon osmotic deflation of vesicles enclosing two aqueous phases that partially wet the membrane, one can observe morphological changes such as vesicle budding (Y. Li, H. Kusumaatmaja, R. Lipowsky and R. Dimova, J. Phys. Chem. B 116:1819, 2012) and/or formation of membrane tubes (Y. Li, R. Lipowsky and R. Dimova, Proc. Natl. Acad. Sci. USA 108:4731, 2011) depending on the competition between the spontaneous curvature of the membrane and the wetting properties of the aqueous phases (R. Dimova and R. Lipowsky, Soft Matter 8:2409, 2012). Phase separation of aqueous polymer solutions in vesicles can lead to stable and retractable membrane nanotubes, which is relevant for membrane area storing and regulation in cells.

Lipid bilayer membranes with in-plane orientational order, such as DPPC in the tilted gel phase, may contain topological defects which induce variations in membrane curvature [1]. To explore the role of such defects in the morphology of lipid membranes, we simulate lipid vesicle shape evolution using a single layer, coarse-grained implicit-solvent model [2], with an extra vector degree of freedom representing in-plane orientational order. For the case of tilt order (so-called "n-atic" order with n=1) we find that the vesicle's final shape is determined by kinetic competition between curvature change and defect motion. If defect motion is relatively fast, the vesicle relaxes to a smooth, prolate ground state with one defect at each end. If defect motion is relatively slow, we observe that the formation of membrane curvature around each defect arrests pair annihilation and traps the vesicle in a disordered, defect-rich state which is deeply metastable. We compare our results with recent experimental studies by Linda Hirst, who showed that vesicles of DPPC cooled into the tilted gel phase develop crumpled, disordered morphologies. Next, we simulate vesicles with in-plane nematic order (n=2) and observe that the resulting ground state shows a range of morphologies depending on the strength of coupling between orientational order and curvature. Lastly, we present a theoretical analysis of the coupling between membrane elasticity and in-plane orientational order that explains the resulting morphologies. Supported by NSF DMR-#1106014. [1] J. Park, T. C. Lubensky, and F. C. MacKintosh, Europhys. Lett. 20, 279 (1992). [2] H. Yuan, C. Huang, Ju Li, G. Lykotrafitis, and S. Zhang, Phys. Rev. E 82, 011905 (2010).

Biological systems are naturally occurring self-assembled and hierarchical systems that involve a multitude of length scales, geometrical shapes and topological variation. Moreover, unlike their inorganic solid counterparts they are elastically soft and therefore easily deformable. Despite extensive structural and physical property characterization, they have not been viewed as topologically distinct bio-molecular systems although their geometrical and shape aspects lend themselves to a new research paradigm similar to nanocarbons. Additionally, these exotic geometries are accompanied by (local) topological networks or interfacial curvature in the same physical system. Motivated by our recent work within the framework of topology and geometry (curvature) for a range of nanocarbons having exotic structural diversity [Gupta and Saxena, J. Raman Spec. 2009; Gupta and Saxena, J. Appl. Phys. 2011], here we attempt to extend and invoke similar approach to understanding the bio-macromolecular systems in the context of minimal surfaces. Bio-macromolecular systems including bio-membranes (planar or curved), microtubules (cylindrical), vesicles (ring-shaped or toroidal), rods and cone (conical) cells, amphipathic (helical screw) molecules, globular proteins and DNA (double-helix and complex), in this contribution catenoids (synthetic or natural ion-channel membrane proteins) and helicoid (beta-sheet proteins) systems are analyzed within the framework of differential geometry in order to obtain important information on topological features such as negative gaussian (K) curvature (since mean curvature H = 0 for minimal surfaces at every point) and bending elasticity (Canham-Helfrich) energy. Through this analysis we hope to derive an overarching and emerging paradigm of bio-macromolecular shape/topology and functionality relationship. Specifically, we examine the geometry, topology and use differential geometric methods to analyze the surface structure of membrane proteins (non-periodic) and Schwarzite (periodic) minimal surfaces. We focus on ion-channels approximated as a catenoid, biological sheets (and graphene nano-ribbon) as a helicoid and certain negatively curved periodic minimal surfaces such as Schwarzite. We also emphasize the transition states from one geometric (and/or topological) form to another and emphasize that curvature leads to nonlinearity that manifests in some form of symmetry breaking or statistical property variation with direct implications for synthetic bio-functionality. This work was initially commenced in collaboration when the author (SG) was working with the University of Pennsylvania and prior to that her CINT User Proposal at LANL was approved.

Over the last two decades, many examples of Low Molecular Weight (LMW) hydrogelators have been demonstrated. These materials have widespread appeal in areas such as biomedical technology by virtue of their rich structural diversity, tunability, low cost and non-covalent nature - which allows for reversible formation and self-repair. By focusing on the self-assembly of small peptide amphiphiles, we have developed a toolbox for controlling the nanoscale morphology of self-assembled systems, specifically Fmoc-protected dipeptides (Fmoc = 9-Fluorenylmethyloxycarbonyl) with a general formula of Fmoc-X₁-X₂. We have utilized a large variety of characterization techniques, including infrared, circular dichroism and fluorescence spectroscopy, electron microscopy, X-ray diffraction and molecular dynamics simulations to help towards the understanding of design rules for peptide self-assembly. First of all, several sequence/structure relations have been observed for these systems, where small changes in hydrophobicity, size or order of the amino acid side chains of the hydrogelator molecule strongly affect the shape of self-assembled nanostructures.(1) Fmoc-Ser-Phe-OMe, formed by the enzyme-catalyzed condensation of Fmoc-Ser and Phe-OMe, was shown to form extended two-dimensional sheets and macroscopic spherulitic structures, whilst small mutations (Ser→Thr or Phe→Leu) gave rise to the formation of flat tapes and twisted fibers, each with different levels of supramolecular chirality. As a general trend, placing a hydrophobic amino acid at the terminal position (X₂) of the protected dipeptide (with X₁ = hydrophilic) generally increases the strength of the hydrogel, compared to a hydrophobic first (X₁ = Tyr) and hydrophilic terminal residue (X₂ = Asn, Glu, Ser, Thr). We have recently shown that the pathway of assembly is a crucial factor in determining, amongst others, the size and shape of the nanostructures.(2) Biocatalytic methods using a variety of enzymes often favor formation of the thermodynamic product, which is important in the elucidation of design rules for these systems and can be vital for biomedical and electronic applications. Finally, we have used Fourier transform infrared spectroscopy and density functional theory calculations to obtain further insight on the molecular level into the buildup of self-assembled β-sheet structures. We are currently investigating the use of 2D-IR spectroscopy as a further probe for the molecular details these materials. References (1) Hughes et al. Soft Matter, 2012, 8, 5595 (2) Hughes et al. Soft Matter, 2011, 7, 10032

Microtubule patternings such as radial or parallel orientations are widely observed both in vivo and in vitro. Several strategies have been explored for controlling the pattern formation in vitro by using counterions, associated proteins, and external force such as gravity, magnetic field, and temperature gradient. Especially, the bending properties and the maintenance of the parallel bundles depending on the specific rigidity attract us from viewpoints of theory, biology, and material. However, discontinuous phase patterns with hierarchy have yet to be discovered. Here we show that the microtubular bundles bend flexibly in hydrodynamic flow to form teardrop patterns like a looped carpet. In highly-concentrated microtubular solution, the same-size teardrop patterns are formed according to the lower critical curvature which is determined by the specific rigidity of microtubules. The pattern-growing process is understood that microtubular bundles with hydrodynamic flow energy are converted to stable teardrop patterns as a higher structure. These self-generating patterns in a stream are exactly ‘a scream of nature&’. We envision that the microtubule pattering with hierarchical structure will provide many guides for material design of higher functions such as biological mass-transportation and information-converting systems.

Environmental concerns related to the declining raw material resources for petrochemical based polymers and increasing amounts of plastic wastes being sent to landfills emphasize the urgent need for the development biodegradable polymers. The biodegradable polymer matrix that was used in this study is Poly (lactic acid) (PLA). Low toughness of PLA was tried to be enhanced by introducing plasticizer PEG, which impedes the tensile properties in the long term, and the deterioration in mechanical properties owing to plasticization was tried to be overcome by nanofiller addition. As nanofiller, naturally occurring halloysite nanotubes (HNT) having a unique elongated hollow tubular morphology and possessing the chemical structure of layered silicate was used [1]. Two HNT types, one local (ESAN HNT) and the imported one (Nanoclay HNT) supplied from Aldrich, were used. At the first, characterization and purification of local HNT was performed. The ESAN HNT was treated with ethylene glycol and it was observed that the mineral sample was mainly comprised of halloysite and did not contain kaolinite, inferred from the MacEwan effect (decrease in basal peak and increase in non-basal peak) that can be observed only for halloysite nanotubes [2]. XRD analysis of raw HNT revealed the presence of impurities, which are most likely gibbsite, quartz and feldspar. In order to remove these non-clay impurities, sedimentation procedure was applied and quartz and feldspar impurities were successfully sorted out from the HNT mineral. For the nanocomposite preparation, 3 and 5 wt% halloysite nanotubes were introduced into both plasticized and unplasticized PLA matrix. Upon the addition of both ESAN HNT (local HNT) and Nanoclay HNT (imported HNT) no improvement was observed in the basal spacing of the clay layers owing to poor interaction between the matrix and the surface of the nanotubes. Hence, the desired tensile properties could not be achieved both for plasticized and un-plasticized composites. Differential Scanning Calorimetry (DSC) analysis showed that HNT mineral inclusion reduced the crystallinity of PLA, whereas, the crystallinity was enhanced by PEG addition at 5 wt% clay loading. However, at this composition the glass transition (Tg) decreased significantly. [1] Churchman G. J., Carr R.M. 1975. Clays and Clay Minerals, 23: 382 - 388. [2] MacEwan D.M.C., 1946. Nature, 157: 157 - 160.

Particles with biphasic chemical composition and anisotropic surface properties present a new type of microparticles known as two-face Janus particles. Janus particles prepared by selective polymer coating of inorganic particles can be used to obtain half-shells upon the release of inorganic cores. Such half-shells present a new class of anisotropic replicas of spherical particles. We fabricate these particles using cubic MnCO3 cores. The procedure includes embedding of the template particles into a sacrificial polymer layer, coating with LbL polymer film followed by release of free Janus particles by dissolution of the sacrificial layer. By applying anisotropic particles as sacrificial cores, one can achieve structures with unusual shapes, for example, open “micro-boxes”, hollow cylinders, hollow tetrahedral structures, half hollow ellipsoids and other shapes.

DNA templates can be used to self-assemble metal or semiconductor nanoparticles into programmable molecular architectures. The interactions between DNA and nanoparticles strongly depend on the size and ligand chemistry of nanoparticles. We performed molecular dynamics simulations to investigate the effect of colloidal gold nanoparticle (GNP) as a function of ligands charge and polarity to its ability to bind to DNA molecules. The surface of GNP was decorated with thiolated alkyl ligands with different terminal functionality such as hydrophobic, polar and charged groups. We observed that uncharged GNPs and GNPs with cationic ligand charge density of less than 10% can only bind to the minor groove of DNA. Whereas GNPs with ligands charge density of higher than 10% can bind to major or minor groove. Binding to major groove result in significant distortion and wrapping of DNA around the GNP corona. The distortions of the DNA helical structure strongly depends on the ligand charge density. Also at higher nanoparticle concentration and low charge densities, the ligand hydrophobicity can disrupt the hydrogen bonding between base pairs of DNA strands and leads to partial denaturation of DNA helix. We observed that by tuning the cationic charge density and polarity of GNP we can control the binding modes and structural mechanics of DNA. Support for this research was provided by the NSF CMMI-1150682 and NSF 's Research Triangle MRSEC (DMR-1121107).

Biological systems are saturated with examples of hierarchical material organization into intricate geometries exploiting a variety of system-strengthening building paradigms. Here we consider the interaction between spider silk material properties with geometric specification of a web system, within an orb web architecture, by using a molecular dynamics-based coarse-grained model. In nature, orb webs are divided into two categories differing by the capture silk used in construction: cribellate orb webs composed of pseudoflagelliform silk coated with dry cribellate threads and ecribellate orb webs using viscid capture silk, composed of flagelliform silk fibers, coated by adhesive glue droplets. Cribellate orb webs are more closely related to ancestral webs and ecribellate orb webs are more abundant and diverse today, implying an evolutionary advantage for the latter. We focus on naturally observed variation in spiral capture silk spanning a wide range of strength and elasticity limits, where cribellate capture silk is generally stronger but less extensible than viscid capture silk. We investigate how the mechanical properties of spiral capture silk effect the behavior of the whole web, illustrating that in webs with more extensible capture silk, the effect of thread strength on web performance is reduced. Essentially, we find that extensible spiral threads require minimal strength for optimized effect within the orb web, as the effect of strength is progressively reduced when extensibility is increased. These findings may be employed more generally in engineered heterogeneous material systems requiring conservation of phases contributing to material strength. We propose that natural structures provide an excellent material template for biomimetic, synthetic materials, providing insight into smarter modification of existing materials through geometric constraints.

We give numerical evidence of the formation of a family of 4-colored chiral network structures self-assembled in blends of ABC and ABD 3-miktoarm star terpolymers constrained to have equal sized A/B and C/D chains respectively. In these new structures the C and D components form a pair of interwoven networks and the minority A and B components together define a hyperbolic film whose mid-surface resembles the Gyroid surface. Thus, the C and D nets are describable by two equivalent but chiral enantiomeric srs-nets. In addition, the A and B components on the Gyroid film are themselves net-like, forming what could be described as 'hyperbolic stripes'. The structures are related to a family of free tilings in the hyperbolic plane and changes systematically as a function of composition.

Mesoporous silica films with cylindrical, bicontinuous or spherical pores up to 40 nm in diameter were fabricated by replicating the morphologies of polystyrene-b-poly(tert-butyl acrylate) (PS-b-PtBA) copolymers using supercritical CO2-assisted infusion and phase selective condensation of tetraethylorthosilicate within the solid template.1-3 The (PS-b-PtBA) copolymers were prepared by Atomic Transfer Radical Polymerization (ATRP). The template structures, including domain packing, orientation and spacing were controlled by adjusting the molecular weight, volume fraction and polydispersity of the block copolymers and by solvent annealing. The structural details imparted to the templates prior to precursor infusion were retained in the mesoporous films. Directed self-assembly4 of PS-b-PtBA templates on topographically patterned substrates was used to control the orientation of cylindrical domains. Replication of these oriented templates yields arrays of well aligned cylindrical channels. The diameters of the channels were controlled by adjusting the molecular weight of the template and could be tuned between 5 and 30 nm. Applications of these optimized channel structures will be discussed. 1. R. A. Pai, R. Humayun, M. T. Schulberg, A. Sengupta, J.-N. Sun, J. J. Watkins, Science 2004, 303, 507. 2. S. Nagarajan, M. Li, R. A. Pai, J. K. Bosworth, P. Busch, D.-M. Smilgies, C. K. Ober, T. P. Russell, J. J. Watkins, Advanced Materials, 2008, 20, 246. 3. H. Chen, T. A. Crosby, M. Park, S. Nagarajan, V. M. Rotello and J. J. Watkins, J. Mater. Chem. 2009, 19, 70. 4. H.-C. Kim, S.-M. Park, W. D. Hinsberg, Chemical Reviews 2009, 110, 146.

Liquid crystal elastomers are fascinating materials for studies of geometry and topology as they can be “blueprinted” with an arbitrary microstructure of the nematic director, and undergo remarkable transitions of shape and curvature under temperature change [1]. Recent studies have examined nematic elastomer ribbons with twisted director microstructure [2]. When heated or cooled, these ribbons twist into helicoids and spirals, and undergo surprising transitions in macroscopic chirality from right-handed to left-handed shapes. Using finite element simulations, we explore the dependence of shape selection and chirality on material and sample properties including ribbon geometry, aspect ratio, director orientation and twist, and temperature. We find that in some geometries, there is a shape transition between helicoids and spirals as a function of the ribbon&’s width/thickness ratio. In other director geometries, this transition is absent and only spiral structures are formed. We demonstrate the mechanism driving chirality reversal of these structures as a function of temperature. We also discuss potential applications of these materials as actuators, microfluidic pumps and valves, and sensors. Supported by NSF DMR- #1106014. [1] C.D. Modes and M. Warner , “Blueprinting Nematic Glass: Systematically Constructing and Combining Active Points of Curvature for Emergent Morphology,” Phys. Rev. E84, 021711 (2011). [2] Y. Sawa, F. Ye, K. Urayama, T. Takigawa, V. Gimenez-Pinto, R. L. B. Selinger and J. V. Selinger, “Shape selection of twist-nematic-elastomer ribbons,” PNAS 108, 6364 (2011).

Layered semiconductors have recently received significant amount of attention for potential use in nanoelectronics, energy harvesting and sensing applications. We explore large-area growth of layered semiconductor, molybdenum disulfide (MoS2). The CVD-based growth consisted of a reaction between molybdenum with sulfur vapor at high temperatures. Raman peaks at 385 cm-1 from in plane bonding and 405cm-1 from out-of-plane bonding confirmed the growth of MoS2. The layered crystal structure only allows for nanosheet thicknesses with a numeric interval of 0.7nm, the thickness of MoS2 monolayer. AFM confirmed the growth thickness to be 2 nm, or trilayered. Transmission Electron Microscopy was used to confirm the crystalline nature, showing layered structure at the edge. Field effect transistors were fabricated to investigate electrical properties. The CVD synthesized MoS2 nanosheet showed semiconducting properties and p-type doped behavior.

Nanofibers are useful for a variety of applications in the biological and material sciences. Specific nanofiber morphologies can be useful for applications from drug delivery to tissue engineering. Rotary Jet-Spinning (RJS) has been demonstrated as an efficient nanofiber production technique using a perforated reservoir rotating at high speeds to produce nanofibers. Previously, an experimental phase diagram of fiber morphology for a single polymer was constructed; however a universal relationship including the effect of polymer structure and solvent volatility on fiber morphology in RJS remains elusive. We hypothesize that through the combination of experiments and theory, a critical universal relationship between surface tension, viscosity, solvent volatility, and polymer structure can be derived which dictates a threshold for uniform fiber morphology. To study how molecular structure and solvent volatility effect fiber morphology, we quantified percentage beading in RJS fibers composed of poly(lactic) acid and collagen in varying solvents. We constructed phase diagrams depicting the boundary between uniform and non-uniform fibers. Results show that increased molecular complexity, indicated by presence and number of side chains, increases centrifugal forces required to form fibers. Additionally, solvent volatility decreases the viscosity required to form continuous fibers. Using these findings and the principles of Rayleigh instability, we derived a physical relationship between surface tension and viscosity which can be used as the basis for a mathematical model predicting uniform fiber formation. Through theory and experiment, empirical and physical models make it possible to control nanofiber morphology for biological applications.

Understanding how the emergence of complex forms and curved shapes in biominerals came about is of fundamental interest, and with practical ramifications for bio-inspired micro- and nano-fabrication strategies. Although the crystallization in the presence of additives has been studied extensively to make complex shapes, the mechanisms for the emergence of curved structures have remained unexplored. We here identify a reaction-diffusion system in which the curved shape of the solidified products is a direct readout of the environmental conditions. We demonstrate that continuous manipulation of the environment during the growth results in finely sculpted solid state materials.

We report the discovery of Mobius, Ring, Figure-8, Hopf-link Crystals in NbSe3, conventionally grown as ribbons and whiskers. We also reveal their formation mechanisms of which two crucial components are the spherical selenium (Se) droplet, which a NbSe3 whisker wraps around due to surface tension, and the monoclinic (P2(1)/m) crystal symmetry inherent in NbSe3, which induces a twist in the strip when bent. Our crystals provide a non-fictious topological Mobius world governed by a non-trivial real-space topology. We classified these topological crystals as an intermediary between condensed matter physics and mathematics. Moreover, we review the interplay between real-space topology and physical properties as universal phenomena. References [1]A Mobius strip of single crystals, S. Tanda et al., Nature 417, 397 (2002). [2]Formation and growth of NbSe3 topological crystals, T. Tsuneta and S.Tanda J. Cryst. Growth 267, 223 (2004). [3]Topologically linked crystals, T.Matsuura et al., J. Cryst. Growth 297, 157 (2006). [4]Topological effect of the superconducting vortex state in a TaSe3 ring crystal, G. Kumagai et al., Phys. Rev. B81, 184506 (2010). [5]Chiral Charge-Density waves, J. Ishioka et al., Phys.Rev. Lett 105, 176401 (2010). [6]Topology-change surgery for crystals, T. Matsuura et al., Phys. Rev. B83 174113 (2011). [7] Topological response in Figure-8 Crystals:.

Semiconductor quantum dots (QDs) realizing biosensors with high sensitivity are usually described as fluorophores having remarkable photostability, large absorption cross section, tunable emission peaks, and high quantum yields. These nanoscale clusters are generally known to show highly size-dependent electronic and optical properties determined by variable energy band gap. These features of the quantum dots are originated from low-dimensional structures in nano length scale. QDs in particular shape and size can exhibit superior optical properties, but favorable structures in nature may not always be same with them. To improve their performance in systematic manner, it is demanded to explore the underlying characteristics of the geometrical structures with the electronic/optical properties. We employed first principle calculations to address the optimal internal and external structures of CdSe quantum dots. Special attentions were put on dimensional analysis on the nanocrystalline structures. Possible internal lattices of wurtzite and zincblend in CdSe were analyzed in terms of shape and size, and external low-dimensional geometries such as quantum spheres (0D), rods (1D), and disks (2D) were investigated in search of energetically favorable geometries. From our calculations on CdSe QDs, quantum rods (1D) are shown more favorable than 0D or 2D in the specific length scale, which is consistent with experimental observations. We discuss the results with analytic predictions based upon geometrical analysis of surface effects.

The interface between the collagen protein and hydroxyapatite in bone represents a critical material interface. While it is known that the nanoscopic structure of bone has significant effect on its mechanical properties, a thorough quantitative understanding of the effect of the material&’s morphology on the mechanical function of the collagen-hydroxyapatite interface remains missing. Here we perform the atomistic modeling of this interface by combining tropocollagens and hydroxyapatite nanocrystals together and investigate its mechanical property by applying tensile forces via steered molecular dynamics simulations. We show the effect of geometry, different crystal surfaces and hydration on the interfacial mechanical properties and discuss the underlying deformation mechanisms of this composite material. We find that the presence of hydroxyapatite significantly enhances the composite&’s tensile modulus compared with a tropocollagen molecule alone. Moreover, we find this stiffening effect is strongly sensitive to the thickness of the hydroxyapatite nanocrystal until a convergence of properties is reached at 2 nm. No significant differences due to the mineral surface (Ca surface vs. OH surface) or due the presence of water are observed in our simulations. Our result agrees well with experimental observations that consistently show the existence of extremely thin mineral flakes of nanometer size in various types of bones. By using an elastic network model, we have also scaled up our atomic simulation results to estimate the surface energy at the interface for larger-scale applications.

Biomimetic membranes composed of lipids, proteins, and other amphiphilic molecules are ultrathin and highly flexible surfaces, which can easily adapt their shape to external perturbations but, at the same time, are sufficiently robust to keep their structural integrity even for strong deformations. As a consequence, biomimetic membranes and vesicles can attain a large variety of different shapes and domain patterns. This polymorphism can be understood in terms of a few material parameters as will be illustrated by some recent results for membrane budding and tubulation induced by aqueous phase separation [1,2,3], membrane engulfment of nanoparticles [4], patterns of membrane domains for free [5] and adhering vesicles [6], as well as for curvature generation in double-membrane disks [7]. [1] H. Kusumaatmaja, Yanhong Li, R. Dimova and R. Lipowsky, Phys. Rev. Lett. 103, 238103 (2009) [2] Yanhong Li, R. Lipowsky, and R. Dimova, PNAS 108, 4731 (2011) [3] R. Lipowsky, Faraday Disc. (2013) DOI: 10.1039/C2FD20105D [4] A. H. Bahrami, R. Lipowsky, and T. R. Weikl, Phys. Rev. Lett. 109, 188102 (2012) [5] Jinglei Hu, T. R. Weikl, and R. Lipowsky, Soft Matter 7, 6092 (2011) [6] T. Rouhiparkouhi, T. R. Weikl, D. E. Discher, and R. Lipowsky, submitted. [7] R. Knorr, R. Dimova, and R. Lipowsky, PLoS ONE 7, e32753 (2012)

The study of low dimensional charge density wave (CDW) materials have been an active research area for several decades. Recent studies have explored the rich phase diagrams these materials exhibit when doped chemically and/or confined in nanoscale dimensions. Recent breakthroughs in the high quality synthesis of CDW materials in the form of nanoribbons and beams offer an exciting pathway to explore new phenomena hitherto unexplored in their bulk counterparts. We report a facile one-step vapour transport process in synthesizing single crystalline nanoribbons of CDW materials such as NbSe₃, TaS₃ and TaSe₃. Structural characterization methods attest to the highest quality of the nanoribbons. Electrical transport measurements and low-frequency noise spectroscopy measurements were carried out simultaneously on single nanoribbons of these materials. Transport measurements show intriguing features near the pinning-depinning transition in the nanoribbons and can be attributed to finite size effects. Noise spectroscopy has been an important tool in materials research due to its close relation to the impurities and structure defects in materials. The noise spectroscopy measurements on single nanoribbons reveal a enhanced weak pinning feature that was not found in bulk samples. Our studies underpin the importance of coupling high quality synthesis of nanomaterials with modern techniques exploring microscopic behaviour in bringing out new phenomena to improve our current understanding of several strongly correlated electron materials.

What makes three dimensional semiconductor quantum nanostructures (QN) so attractive is the possibility to tune their electronic properties by careful design of their size and composition. An often overlooked parameter, which has an even more relevant effect on the electronic properties of the QN, is shape and topology. Gaining a strong control over the electronic properties via shape and topology tuning is the key to access subtle electronic design possibilities. The Dropled Epitaxy (DE) is an innovative growth method for the fabrication of quantum nanostructures with highly designable shapes and complex morphologies. With DE it is possible to combine different QN, namely quantum dots, quantum rings and quantum disks, with tunable sizes and densities, into a single nanostructure, thus allowing an unprecedented control over electronic properties. Unlike the standard self-assembly technique, DE does not rely on strain for the formation of three-dimensional crystals. DE is based on the pulsed deposition of III and V column elements at controlled temperatures and fluxes. The first step of DE is the formation, in a Molecular Beam Epitaxy environment, of nanoscale reservoirs of metal atoms on the growth surface in forms of nanometer size droplets with small size dispersion. This is achieved in a group V free environment. Second, and more relevant for the QN shape control, is the pulsed supply of group V elements at different temperatures and fluxes, for the transformation of the metallic droplet into the QN. The possibility to control, through flux and temperature, the transformation kinetics of the metal droplets in to III-V nanocrystals allows for the formation of QNs with complex and controlled shapes. Since the change in shape of a QN often leads to a change in electronic state characteristics, the phenomena arising from shape design are very rich. The theoretical calculations the electronic states of the obtained complex QN show a good agreement with the photoluminescence emission of the fabricated samples. In conclusion, DE allows for the realization of complex QNs where single building blocks, such as quantum dots, quantum rings and quantum disks, can be combined together with a high shape flexibility. DE can be therefore used as basis for the conception of novel devices in optoelectronics and quantum information fields, as well as for the investigation of phenomena in fundamental physics allowing the manipulation of the electronic wave function topology.

Nanotechnology industries today require real-time and quantitative sizing of nanoparticles for semiconductor applications, nanomaterials characterization, and liquid filter testing. Currently these applications use light scattering techniques to size nanoparticles in liquids (i.e. DLS, laser diffraction, optical particle counting). There are systematic limitations to these techniques, however. If the optical properties of the suspension are unknown, the sizing uncertainty can be large. Data inversions can be challenging, sometimes requiring a priori information about the size distribution or optical properties of the material. Tradeoffs are made between sensitivity and size resolution; current techniques with a wide size range (such as DLS and laser diffraction) measure bulk properties instead of analyzing individual particles, but instrumentation that analyze individual particles (such as optical particle counters) cannot detect particles <40 nm. SEM can be used to do quantitative, high resolution sizing, but results are not real-time. By applying well-established gas-phase particle sizing techniques to liquid particle technology, quantitative measurements of particle size distributions can be made that are impossible to achieve with current liquid-phase techniques. In this paper we present a technique using Scanning Mobility Particle Sizing (SMPS), widely used as the standard method to measure airborne particle size distributions, for sizing and counting nanoparticles in liquid suspensions down to below 5 nm. A unique Nanoparticle Nebulizer (NN) is paired with an SMPS spectrometer to leverage the high degree of size accuracy and resolution achievable with mobility-based sizing. The nebulizer creates an aerosol of the liquid suspension under controlled temperature and pressure conditions, and the SMPS provides absolute number concentration and a quantitative nanoparticle size distribution of the liquid suspension. The real-time (<2 min) technique is used either online for process measurements or off-line for measuring the size distribution of individual samples. Nanoparticles down to 5 nm are sized with good accuracy and resolution. The system has been used to characterize a variety of aqueous colloidal suspensions including gold, alumina, PSL, colloidal silica, and macromolecules such as dextran. Real-time measurement of the coefficient of variation (CV) of PSL and gold size distributions is in excellent agreement with the CV published by manufacturers. The NN-SMPS has also been used to characterize CMP polishing slurries and measure removal efficiency of liquid filters as a function of particle size, filter pore size, and filter loading. Particle sizing data from these studies is also presented. References Van Schooneveld, G., Litchy, M. and Grant, D. (2010) Proc. 2010 Int. Conf. on Planarization/CMP Tech, Phoenix, AZ, 348-351. Grant, D. and Beuscher, U. (2009) Ultrapure Water J. 26, 34-40.

In plane dynamic-mechanical properties of TiO2 nanotube arrays are assessed by a vibrating reed experimental study. Using the vibrating reed method the TiO2 nanotube array is excited to vibrations and the damping and exact frequency is determined from the free decay. The TiO2 nanotube arrays were synthesized by repeated anodization in an electrolyte containing ethylene glycol, ammonium fluoride and water. Due to a high degree of porosity and the details of the topology of the structures, the arrays reveal a very low elastic modulus, while significant damping due to the amorphous nature of the tube walls and anelastic deformation behavior are detected. Hence biocompatible coatings of flexible membranes as application for TiO2 nanotube arrays are clearly conceivable. Both, storage and loss moduli, are dramatically affected by the presence of surface adsorbates, as demonstrated exemplarily for air and water, respectively. The received activation enthalpies for desorption of air exposures lies perfectly in the same order of magnitude observed by other authors in thermal desorption spectroscopy (TDS) studies of O2 on TiO2 arrays. Interestingly the impact of water desorption on the mechanical properties gives two different activation enthalpies hinting at two different rate-limiting processes which is already stated by literature. As for impact of adsorbate type on mechanical properties, different adsorbates explicitly leave different fingerprints on the signatures of the mechanical properties. Thus this finding paves the way for highly sensitive and economical adsorbate detectors or - vice versa - adsorbate mediated actuators. [1] K. Fischer and S.G. Mayr, Adv. Mat. 23, 3838 (2011)

Curiosity about the chemistry in the atmosphere of an old red giant star about a light year in diameter (i.e. 10,000 million, million meters) resulted in advances in technology at nanometer scale i.e. 100 millionth of a meter which is some million, million, million, million times smaller. When Galileo first used his telescope and realized that the phases of Venus provided the incontrovertible evidence which confirmed the Copernican heliocentric system it cemented his position as one of, if not the, “Father of Science”. Thus Science itself was born out of curiosity, not out of expedience, and it is still true today that almost all major breakthroughs are made by the openly curious who generally discover what those with more focused minds tend to overlook. Particularly fascinating, curious and crucial has been the role that the element carbon has played in almost every aspect of the development of our understanding of both the physical and natural sciences. Carbon chemistry is uniquely profuse, i.e. Organic Chemistry. As it is the basis of biology, it is hard to conceive that life could be based on any other element. The most recent big surprise that the element had up its sleeve was the existence of C60, Buckminsterfullerene, the third well-defined form of carbon - the other two being graphite and diamond. The discovery of this molecule was made serendipitously during laboratory experiments which attempted to simulate the conditions in some stars. Follow up work from the C60 discovery led to the re-discovery of the carbon nanotubes which promise paradigm shifting advances in materials engineering and catalyzed the birth of Nanoscience and Nanotehnology (N&N). Research on carbon chain molecules at Sussex in the mid-1970&’s led to the detection of these chains in interstellar space by radio-astronomy together with Canadian astronomers. A little later these species were detected in red giant carbon stars. It was during experiments, using an advanced technique, developed at Rice University for studying clusters, to probe the formation of the chains in these stars that the C60 cage was discovered serendipitously in 1985. Amazingly in 2010 the tell-tale fingerprint signature of C60 was found in infrared spectra obtained by NASA&’s Spitzer satellite telescope. This sequence of events is yet another example of the remarkable way in which fundamental science, in particular in this case the fascination with space has led to major breakthroughs with important implications for innovative technological applications on Earth. The history of scientific progress carries a serious health warning for those who think that fundamental science can be steered by bureaucratic decision-making and the story of the discovery of “Buckminsterfullerene - The Third Form Carbon” and its key role in the birth of Nanoscience and Nanotechnology is yet another example.

Highly deformable yet chemically inert atomically thin materials animate a wide range of novel structural, optical, and electronic phenomena. For example, the division of surrounding space into two disconnected zones by an impenetrable suspended sheet enables adsorption of otherwise highly co-reactive species in opposite subspaces, with an intense cross-sheet charge transfer that can generate a nanoscale Stark effect, strong non-adiabatic effects, unique open-shell character, and broad band gap tuning. New physics also results when the same species is adsorbed to both sides, with unusual "which-side" symmetry breaking at certain chemical potentials. Simple charges constrained to a cylindrical manifold also show new dynamics; for example domain boundaries between different phyllotactic domains transport charge dipoles along the cylinder axis in response to a rotating transverse electric field. Surprisingly, the enclosed domain of monopole charges can be rotate in a sense opposite to that of the applied field.

High-density carbon nanotube networks (CNNs) continue to attract interest as active elements in nanoelectronic devices, nanoelectromechanical systems (NEMS) and multifunctional nanocomposites. The interplay between the network nanostructure and its properties is crucial, yet current understanding remains limited to the passive response. Here, we employ a novel superstructure consisting of millimeter-long vertically aligned single walled carbon nanotubes (SWCNTs) sandwiched between polydimethylsiloxane (PDMS) layers to quantify the effect of two classes of mechanical stimuli, film densification and stretching, on the electronic and thermal transport across the network. The network deforms easily with an increase in the electrical and thermal conductivities, suggestive of a floppy yet highly reconfigurable network. Insight from atomistically informed coarse-grained simulations uncover an interplay between the extent of lateral assembly of the bundles, modulated by surface zipping/unzipping, and the elastic energy associated with the bent conformations of the nanotubes/bundles. During densification, the network becomes highly interconnected yet we observe a modest increase in bundling primarily due to the reduced spacing between the SWCNTs. The stretching, on the other hand, is characterized by an initial debundling regime as the strain accommodation occursvia unzipping of the branched interconnects, followed by rapid rebundling as the strain transfers to the increasingly aligned bundles. In both cases, the increase in the electrical and thermal conductivity is primarily due to the increase in bundle size; the changes in network connectivity have a minor effect on the transport. Our results have broad implications for filamentous networks of inorganic nanoassemblies composed of interacting tubes, wires and ribbons/belts.

Functionalized graphene materials are attractive candidates for novel applications in the fabrication of nanodevices or advanced composites. Here we apply molecular dynamics simulations to investigate the assembly, morphology and interfacial properties of graphene ribbons and sheets functionalized by hydroxyl groups. Our results show that by designing the location and density of the functional groups, the graphene ribbon self-assembles into a double-helix conformation (similar as the double-helix DNA) with a defined folded structure and much lower conformation energy. This folded structure has a much higher persistence length which is four times more than that of the pristine graphene ribbon. We demonstrate that the hydrogen bonds formed between the functional groups at different surfaces crucially account for this morphology change, which is similar to the driving forces of self-assembly in many biological protein systems. We propose that such functionalized graphene materials could be employed to achieve the bottom-up design of structural materials with tunable mechanical properties as they are expected to achieve multiple mechanical functions under varied conditions.

Bio-inspired synthesis involves the design and synthesis of programmed primary structures that are instructed to undergo intramolecular and intermolecular self-assembly, self-organization and the other sequence of events involved in the emergence of complex molecular systems via the same principles as the first principles used by complex biological systems. Since the mechanism of transfer of structural information is not understood, primary structures responsible for the creation of complex systems and functions cannot be designed. Complex systems are identified by what they do, display organization without a central organizing authority, and therefore are emergent, and also by how they may or may not be analyzed; they cannot be understood by analyzing their individual parts in isolation. The major features that characterize complex systems are adaptation or self-control, self-organization and emergence (1). Some also exhibit self-repair and memory. Therefore, complex systems cannot be designed or engineered. Examples of complex systems include social and political organizations, financial and economic systems, life, highways, the internet, the power grids, metabolic pathways, most biological systems, some molecular systems and selected chemical reactions. Complex systems are different from complicated systems that are not characterized by adaptation or self-control, self-organization and emergence and therefore, they can be understood in isolation, engineered and designed. Complex biological systems are emerging from biological macromolecules and molecules with a precise primary structure programmed to mediate the creation of a particular biological system. However, even in biological systems it is not yet understood how a primary structure is selected for a particular function. This lecture will discuss the elaboration of strategies and methods for the bioinspired synthesis of primary structures responsible for the emergence of selected examples of mimics of complex biological systems exhibiting biological functions including the cell membrane by using self-assembling dendrons, dendrimers and other building blocks (1,2,3). The lecture will also address the fundamental question: will the design and/or prediction of programmed primary structures that are responsible for the emergence of the simplest mimics of the cell membrane be possible? Lessons learned from complex molecular systems will be applied to the design of new drug delivery devices inspired from the cell membrane and other examples of bioinspired complex systems with biological functions (2, 3). References: (1) Rosen, B.M.; Wilson, C.J.; Wilson, D.A.; Peterca, M.; Imam, M.R.; Percec, V. Chem. Rev. 2009, 109, 6275-6540. (2) Percec, V.; Wilson, D.A.; Leowanawat, P.; Wilson, C.J.; Hugh, A.D.; Kaucher, M.S.; Hammer, D.A.; Levine, D.H.; Kim, A.J.; Bates, F.S.; Davis, K.P.; Lodge, T.P.; Klein, M.L.; DeVane, RT.H.; Aqad, E.; Rosen, B.M.; Argintaru, A.O.; Sienkowska, M.J.; Rissanen, K.; Nummelin, S.; Roponen, J. Science 2010, 328, 1009-1014. Peterca, M.; Percec, V. Leowanawat, P.; Bertin, A. J. Am. Chem. Soc. 2011, 133, 20507-20520. (3) Rosen, B.M.; Peterca, M.; Morimitsu, K.; Dulcey, A.E.; Leowanawat, P.; Resmerita, A.-M.; Imam, M.R.; Percec, V. J. Am. Chem. Soc. 2011, 133, 5135-5151.

Through numerical simulation using knot invariants we can explicitly evaluate fundamental physical quantities of ring polymers with fixed topology in solution, from which we derive general theoretical results by applying physical interpretation such as the renormalization group arguments. For an illustration, we consider knotted ring polymers in solution. We evaluate the diffusion constants of them through Browninan dynamics. We show that the ratio of the diffusion constant of a ring polymer with a given nono-trivial knot type to that of the trivial knot is given by a constant with respect to the molecular weight of the polymers. Furthermore, the ratio is determined by the average crossing number of the ideal spatial configuration of the knot, which we call the ideal knot for the knot [1]. We also evaluate diffusion constants of polymers with nontrivial topology such as linked ring polymers [2], and polymers with tadpoles and theta-curves. We also introduce a new probability measure on closed polygons, by which we can generate an ensemble of random polygons with any given topology [3]. We discuss various applications of the new measure to polymers with complex topology. Ref: [1]: N. Kanaeda and T. Deguchi, Universality in the diffusion of knots, Phys. Rev. E Vol. 79, 021806 (2009); [2] N. Kanaeda and T. Deguchi, Universal ratios in the dynamics of open and closed chains of linked ring polymers in solution via Brownian dynamics, Prog. Theor. Phys. Supplement Vol. 191 (2011) 146--155. [3] J. Cantarella, T. Deguchi, and C. Shonkwiler, Probability Theory of Random Polygons from the Quaternionic Viewpoint, arXiv:1206.3161.

We introduce a general, efficient method to completely describe the topology of individual grains, bubbles, and cells in three-dimensional polycrystals, foams, and other multicellular microstructures. This approach is applied to two classical three-dimensional microstructures: one resulting from normal grain growth (mean curvature flow) and another resulting from a Poisson-Voronoi tessellation of space (random). Grain growth microstructures are dominated by grains with a small set of topologies; this is true to a much smaller extent in the Poisson-Voronoi microstructures. Grains in grain growth microstructures are also significantly more (topologically) symmetric than those in Poisson-Voronoi microstructures. The differences between these two microstructures are likely associated with the energy-minimizing nature of the curvature-flow process in normal grain growth, which is absent in the Poisson-Voronoi microstructures. The frequencies of particular grain types and the average order of their symmetry groups can be used to classify other cellular microstructures. We demonstrate that the frequency of high symmetry cells can differ in similar-looking network microstructures by several orders of magnitude -- providing a simple method to distinguish between microstructures.

The average spacing in aligned nanofiber system strongly influences the physical and transport properties of the bulk material. Because most studies either neglect the nanofiber coordination, or assume that the nanofibers in the system assume either square or hexagonal packing (coordination numbers 4 and 6), there is a need for a model that provides an analytical relationship between the average inter-fiber spacing and the nanofiber volume fraction. A theoretical model for the inter-fiber spacing as a function of nanofiber volume fraction is developed, and a relationship between average coordination, nanofiber diameter, and nanofiber volume fraction is reported for the first time. The model can be used to infer the effective coordination number of nanofiber arrays of varying fiber diameters, and a study for a vertically aligned carbon nanotube (VACNT) system with 8 nm diameter carbon nanotubes (CNTs) is presented. In this study, the average inter-CNT spacing of VACNT forests of varying CNT volume fractions, ranging from 1 to 20 volume %, was determined using Scanning Electron Microscopy (SEM). By combining the theoretical model with empirical data, a working semi-analytical model for the average inter-CNT spacing in a forest as a function of volume fraction is developed. This model shows that the average coordination of the CNT arrays is a function of the CNT volume fraction, and that the average inter-fiber spacing as a function of nanofiber volume fraction cannot be successfully modeled using either square or hexagonal packing. Finally, the model is applied to other aligned nano and microfiber arrays with average fiber diameters greater than 100 nm, and the model predicted average inter-fiber spacings are compared to experimental data previously reported.

Carbon Nanoscrolls (CNSs) are one of the many structures from the graphene family and consist of graphene layers rolled into papyrus-like structures. Since both ends of the scrolled sheet are free, these structures present some very interesting properties which contrast with those of carbon nanotubes. CNSs present a very large solvent accessible surface as well as great radial flexibility[1]. Also, it has been shown that small charge injections produce large changes on the radius, paving the way for the use o CNSs as electro-actuators. Despite these quite interesting properties, these structures have not been as widely studied as other carbon-base structures like CNTs and fullerenes. This can be due to in part attributed to synthesis difficulties. While CNSs can be formed as a sub product of CNTs by methods like the arc-discharge, high yield and controlled synthesis is still a challenging issue. Production by successively exfoliation of highly oriented pyrolitic graphite (HOPG) in solution followed by strong sonication has been proven efficient[2], but provides very little control. In a recent work, Zhang et al[3] have proposed a physical route to CNSs which would provide the possibility of producing in a controllable way high-quality single walled carbon nanoscrolls. In this work we further investigated, through the use of molecular dynamics simulations, this proposed method in which a CNT is used to trigger the scrolling process of a graphene sheet deposited over a SiO substrate. Our results show that by appropriate etching of the substrate, creating for instance microchambers on the substrates and depositing the membranes over it (as recently experimentally realized [4]), the scrolling process can be significantly improved. This approach is completely general and could be used for other two-dimensional systems, as for instance boron nitride (BN) membranes. BN scrolls have been theoretically predicted to exist [5], but have not been yet synthesized. [1] Braga S F, Coluci V R, Legoas S B, Giro R, Galvao D S and Baughman R H 2004 Nano Lett. 4 881 [2] Viculis L M, Mack J J and Kaner R B 2003 Science 299 1361 [3] Zhang Z.and Li T., 2010 Appl. Phys. Lett. 97, 081909 [4] Bunch J S, Verbridge S S, Alden J S, et al., 2008 Nano Lett. 2008 4 2458 [5] Perim E and Galvatilde;o D. S., 2009 Nanotechnology 20, 335702.

Charged colloidal particles present a controllable system for study a host of condensed matter/many body problems such as crystallization. 2D crystals are invariably hexagonal. Hexagons perfectly tile a flat plane but a soccer ball requires exactly 12 pentagons dispersed among the hexagons on its curved surface. Pentagons and hexagons are positive and negative topological charges, disclinations, sources for positive and negative curvature. But we have discovered that "Pleats", grain boundaries which vanish on the surface (and play a similar role to fabric pleats) can provide a finer control of curvature. We experimentally investigate the generation of topological charge as flat surfaces are curved. For positive curvature, domes and barrels, there is one pentagon added for every 1/12 of a sphere. Negative curvature is different! For capillary bridges forming catenoids, pleats relieve the stress before heptagons appear on the surface. Pleats are important for controlling curvature from crystals on surfaces, to the shape of the spiked crown of the Chrysler building. Adding a particle to a flat surface produces an interstitial - usually an innocuous point defect. On a curved surface interstitials are remarkable, forming pairs or triplets of dislocations which can fission dividing the added particles into fractions which migrate to disclinations. *With William Irvine and Mark Bowick.

We establish that equally-spaced smectic configurations enjoy an infinite-dimensional conformal symmetry and show that there is a natural map between them and null hypersurfaces in maximally-symmetric spacetimes. By choosing the appropriate conformal factor it is possible to restore additional symmetries of focal structures only found before for smectics on flat substrates.

Controlling topological defects and liquid crystal (LC) phases in three dimensions (3D) is of particular interest to the generation of blue phases and other topologically structured materials, which will lead to possibly disruptive display technologies. However, it has been experimentally challenging to realize the 3D topology. Here, we investigate formation of 3D geometries of smectic-A (SmA) LCs guided by nanoparticle assembly and the underlying substrate. When the surface chemistry and substrate geometry (here 1D channels) promoted planar alignment of LC molecules, hexagonal arrays of toric focal conic domains (TFCDs) were formed due to competing effects of planar anchoring at the LC/substrate interface and homeotropic anchoring at the LC/air interface. When the silica nanoparticle surface was functionalized by fluorosilane, they spontaneously phase separated from the SmA LCs and aggregated only in the TFCDs at the LC/air interface, which in turn altered the LC anchoring to planar conditions in these regions. In contrast, unmodified silica particles were found embedded within LC layers, breaking the ordered symmetry of SmA film. By imposing nanoparticles with variable surface chemistry, we added new dimensions to control geometries of smectic LCs in 3D, which could shed new light on ways to engineer functional complex structures.

Hybrid organic-inorganic nanoparticles with well-controlled morphology are currently of great interest for numerous applications. Synthetic routes leading to robust aggregates made of nanoparticles of different chemical natures which are associated in a controlled manner (i.e. number of nanoparticles and geometrical arrangement) are especially investigated as potential “colloidal molecules”. Our strategy is based on a seeded emulsion polymerization process leading to biphasic particles, which are composed of spherical silica spheres surrounded by a varying number of polystyrene (PS) nodules. The hydrophilic surface of the silica seed particles (50-400 nm) needs to be previously functionalized. In such conditions, the nucleation/growth of the PS nodules is highly favored at the silica surface, leading to multipod-like morphologies : bipods, tetrapods, hexapods, octopods, etc. While varying experimental conditions, the key parameters were evidenced. The talk deals with recent insights in the high yield and repeatability of the synthesis process, the thorough characterization of some multipod-like clusters by cryo-electron tomography, and the development of a model to help the understanding of the formation mechanism of almost pure suspensions of well-defined clusters.

Topological defects pervade a wide range of physical systems, from superconductors to smectic liquid crystals. The behavior and interactions of such singularities impart many materials with a wealth of rich behavior. Just as flux vortices in the Abrikosov phase of type II superconductors allow magnetic field to penetrate the sample, so too do screw dislocations relieve the geometric frustration between flat layers and macroscopic chirality present in the smectic. An explicit deconstruction of surfaces into their topological constituents provides a unique language with which to describe the properties of many diverse systems. Extracting the underlying topology of a surface boils down to an exercise in complex analysis. Linear systems often produce harmonic surfaces which possess height functions satisfying the two dimensional Laplace equation. Elliptic functions, generalizations of trigonometric functions, are the generic solutions of this problem. Merely specifying the zeroes and poles in a phase field completely defines the topology of the resulting surface. The properties of elliptic functions vastly simplify both the analytic and numeric calculations of the energy. We use this analysis to illustrate two different systems: a system of pores connecting layers of a bicontinuous lamellar system described by Riemann's minimal surfaces and the hierarchical structure of the helical nanofilament phase of bent core smectics.

Triphilic star-polyphiles are short-chain oligomeric molecules with a radial arrangement of hydrophilic, hydrocarbon and fluorocarbon chains linked to a common centre. As a consequence of their star-shaped geometry, these polyphiles can only self-assemble along one-dimensional lines (triple lines), and not along surfaces, which opens the path to a wealth of possible novel nanostructures [1-4]. We will present the most likely model structures based on theoretical considerations, and compare them to our experimental findings (SAXS and SANS). Our first set of molecules, which is based on one central benzene ring [4], exhibits liquid crystalline structures that structurally resemble type-2 lipid mesophases. However, the hydrophobic matrix is split into hydrocarbon and fluorocarbon domains, as shown by a systematic neutron contrast variation series. As an example, a very complex liquid crystalline structure based on the gyroid bicontinuous cubic phase [5-6] emerges as a candidate which is in agreement with theoretical considerations, molecular dimensions and experimental data. The resulting pattern is perhaps the most complex 3D self-assembly of fluids yet known, with multiple interwoven microdomains. In addition to the pair of (right- and left-handed) water networks, it contains stacks of mutually catenated fluorocarbon arrays forming “chicken-wire” nets perpendicular to the four [111] cubic directions, as well as hydrocarbon helical columns, threaded between the fluorocarbon and water nets, along the 6 distinct [110] directions. [1] Hyde S.T., Schroeder G., Curr. Opinion in Colloid and Interface Science 2003, 5-14 [2] Kirkensgaard J.J.K. and Hyde S.T., PCCP 2009, 11, 2016 - 2022 [3] Hyde S.T., de Campo L., Oguey Ch., Soft Matter 2009, 5, 2782-2794 [4] de Campo L., Varslot T., Moghaddam M., Kirkensgaard J., Mortensen K., Hyde S.T., PCCP 2011, 13(8), 3139-3152 [5] Hyde S.T., Oguey C., European Physical Journal B 2000, 16(4), 613-630 [6] Evans, M., PhD thesis 2011, ANU, “Three-Dimensional Entanglement: Knots, Knits and Nets”

We show that quasi two-dimensional colloidal membranes composed of bi-disperse chiral rod-like viruses exhibit phase separation where long or short rods form domains or "rafts" within the membrane. These domains are self-limited and organize themselves into a crystalline lattice. We hypothesize that these domains form to alleviate chiral frustration observed in mono-disperse membranes, in which twist is expelled from the membrane bulk. By varying the stoichiometric ratio between the longer and shorter rods, the shape, size, and density of rafts can be varied. In addition to 2-D membranes, we also observe the formation of three-dimensional membranes with negative Gaussian curvature at specific stoichiometric ratios.

Growth of high-density nanowire arrays is often shaped by Inter-nanowire interactions. In this talk, we focus on an extreme instance, i.e. the helically-coiled coalescence of polar semiconducting nanowires. The long-range electrostatic interaction between the polar side-facets of opposing nanowires offsets the elastic costs associated with coalescence of the nanowires. We study the resultant interplay between geometry and mechanics using combination of systematic experiments on VLS growth GaAs nanowires, and semi-quantitative theoretical frameworks. The variation of the pitch associated of the helically coiled region with the length and radius of the nanowires yields the strength of the electrostatic interactions, which in turn yields estimates on the surface charge densities that drive the coalescence. The combination of elastic and electrostatic energies associated with the pre-coalescence region allow us to pinpoint the location of the initial coalescence. We present our results as a stability diagram that captures the dependence of the final geometry on initial distance between the nanowires, and the total length of the nanowires.

Indium Tin Oxide (ITO) electrodes are often used in organic electronic devices due to their superior transparency and conductance, however they are also brittle, expensive and their fabrication requires vacuum conditions which restrict scale-up. In this work we present the fabrication of transparent Au-Ag Metal Nanowire Mesh (MNWM) electrodes as a possible alternative to the traditional ITO electrodes. The MNWM electrode can be easily fabricated by an all solution process on various substrates including flexible ones such as plastics and on organic layers such as organic semiconductors. The electrode fabrication process involves the reduction of gold and silver ions, which have initially formed a complex with an amphiphilic surfactant. The substrate of choice is dipped in the solution right after the initiation of the reduction reaction, resulting in the formation of a random nanowire mesh at the substrate-solution interface. A simple solution dipping post-treatment is applied to the obtained nanowire electrode to stabilize the nanowires by changing the morphology of the electrode. Overall, the fabrication of our transparent electrode involves two simple solution dipping steps. The geometry and topology of the nanowire mesh, which determines the conductive, roughness and transparency properties of the electrodes, can be controlled by the fabrication process. Organic Light Emitting Diodes (OLEDs) were fabricated using the MNWM electrodes in order to compare their performance to ITO based organic electronic devices. The electrodes used for these devices had transmittance and sheet resistance values of ~91% (at 590 nm) and ~165 Omega; sq respectively. Nanowire protrusions in the topology may cause short circuits in the fabricated OLED devices, however we have found that these could be repaired to present normal OLED behavior by burning shorting nanowires which could be beneficial for applications such as roll-to-roll printing.

Topological insulators are materials in which the electronic wavefunctions are topologically nontrivial as a result of spin-orbit coupling. One consequence is the existence of protected massless surface states as observed in experiment. This talk focuses on two other consequences: the momentum-space geometry of the wavefunctions determines part of the magnetoelectric effect in all materials (including multiferroics), and also determines the response to real-space curvature. The latter leads to a novel Aharonov-Bohm effect and protected mode at nonzero magnetic flux in nanowires. In closing we discuss how nanostructuring of topological materials can lead to new transport processes with potential applications to charge-based logic and to thermoelectricity.

Topological insulators possess a metallic surface state of massless particles, known as Dirac fermions whose spin is coupled to their momentum. The realization of this in Bi2Se3 has sparked considerable interest owing both to the potential for spintronic devices and in the investigation of the fundamental nature of topologically non-trivial quantum matter. However, the conductivity of these compounds tends to be dominated by the bulk of the material owing to chemical imperfection, making the transport properties of the surface illusive. To this end, the orbital quantization provided by high magnetic fields is invaluable in disentangling the conductivity contributions. For bulk materials, we have systematically reduced the number of bulk carriers in the material Bi2Se3 to the point where a modest magnetic field can collapse them to their lowest Landau level. Beyond this field, known as the three-dimensional (3D) 'quantum limit', the signature of the 2D surface state can be seen. At still higher fields, we reach the 2D quantum limit of the surface Dirac fermions. In this limit we observe an altered phase of the oscillations, which is related to the peculiar nature of the Landau quantization of topological insulators at high field. Furthermore, we observe quantum oscillations corresponding to fractions of the Landau integers, suggesting that correlation effects can be observed in this new state of matter.

In addition to conventional topological insulators where surface states arise as a result of spin-orbit interactions, it has been proposed that surface states can also arise as a result of crystal symmetry in topological crystalline insulators¹. It has been predicted that the surfaces of the Sn_1-xPb_xTe can host this new topological crystalline phase². We have therefore grown epitaxial SnTe thin films on Si (100) and (111) by molecular beam epitaxy and sputtering. SnTe is known to be strongly p-type. We thus attempt to alleviate the problem of Sn vacancies in SnTe by alloying it with PbTe or by doping it with Bi or Pb. We measure carrier concentrations lower than 1 x 10²⁰ holes per cm³ in the doped and alloyed samples. When Pb is introduced, the mobility is highest at 148 cm²/Vs. The mobility and the carrier density are of the same order of magnitude as for Bi₂Se₃ and Bi₂Te₃. We report electronic transport results down to T = 2 K. Robust weak antilocalization is observed in the magnetoresistance at low fields in Pb-doped, Bi-doped and undoped SnTe, which can result from strong spin orbit interactions in the bulk or from the existence of helical surface states. In summary, we show that the Sn_1-xPb_xTe is a promising candidate material for studying topological crystalline phases since the Fermi level can be easily tuned by introducing Pb into the lattice. Work supported by NSF-DMR-0907007 and NSF-DMR-0819762. JSM is partly supported by NSF-DMR 0504158 and ONR N00014-09-1-0177. ¹L. Fu, Phys. Rev. Lett. 106, 106802 (2011). ²T. H. Hsieh et al. arxiv: 1202.1003.

Due to the strong spin-orbit interaction of 5d electrons and the geometric frustration of the tetrahedral lattice, the rare-earth pyrochlore iridates have been proposed to harbor nontrivial topological ground states, such as Weyl semi-metal and topological Mott insulators[1,2]. So far most of the experimental results are restricted on the bulk properties of polycrystalline or single crystal samples, which revealed a magnetically coupled metal-insulator transition that can be tuned by either rare-earth ionic radius or pressure[3,4]. In this talk we report the growth and characterization of epitaxial thin film of pyrochlore iridates. Preliminary results of magnetic and transport experiments will also be discussed. The fabrication of thin film offers a new platform for studying the exotic surface/interfacial properties of this class of materials. [1] D. A. Pesin and L. Balents, Nat. Phys. 6, 376 (2010). [2] Xiangang Wan, Ari M. Turner, Ashvin Vishwanath, and Sergey Y. Savrasov, Phys. Rev. B 83, 205101 (2011) [3] K. Matsuhira, M. Wakeshima, R. Nakanishi, Y. Yamada, A. Nakamura, W. Kawano, S. Takagi, and Y. Hinatsu, J. Phys. Soc. Jpn. 76, 043706 (2007). [4] F. F. Tafti, J. J. Ishikawa, A. McCollam, S. Nakatsuji, and S. R. Julian, Phys. Rev. B 85, 205104 (2012)

Topological crystalline insulators are new topological states of matter which arise from the spatial (translation and point group) symmetries of crystalline solids. I will describe our recent theoretical prediction of topological crystalline insulators in the SnTe material class (SnTe, PbTe, PbSnTe and PbSnSe). As a hallmark of their topological nature, these materials possess high-mobility two-dimensional chiral Dirac fermion surface states, in which a continuously tunable band gap can be achieved by strain or magnetic/electric field. A variety of technological applications will be discussed. Several very recent photoemission studies have observed the predicted surface states and are attracting great interest in this new generation of topological materials.

We present topological electronic structures of thallium based ternary chalcogenides TlMQ2, where M (Bi, Sb) and Q ( S, Se, Te), and Weyl semimetals in TlBi(S1-xSex)2 and TlBi(S1-xTex)2 . All calculations are done using VASP (Vienna Ab-initio Simulation Package) code with projected augmented wave basis and PBE type generalized gradient approximation for both the bulk and surface calculations. All structures were fully optimized including volume and ionic optimizations. Our calculations show that these compounds have a well defined band gap between the bulk conduction and valence bands at every k-point in the Brillouin zone. They all possess a single-Dirac-cone conducting surface state except for TlBiS2 and TlSbS2. We thus conclude that all investigated compounds with the exception of TlBiS2 and TlSbS2 are non-trivial topological insulators. Further we study the topological phase transition at the critical concentration x=0.5 in TlBi(S1-xSex)2 and TlBi(S1-xTex)2 by explicitly breaking the inversion symmetry in the layer by layer growth in the order of Tl-Se(Te)-Bi-S . At the topological critical point we obtained Weyl semimetal with six non-degenerate spin polarized Dirac cones along Γ - L direction in the bulk Brillouin zone. We compare and contrast our findings with earlier theoretical computations [1,2] and experimental work [3,4,5] on this series of compounds. [1] H. Lin, R. S. Markiewicz, L. A. Wray, L. Fu, M. Z. Hasan, A. Bansil, Phys. Rev. Lett. 105, 036404 (2010). [2] B. Yan, C.-X. Liu, H-J Zhang, C.-Y. Yam, X.-L. Qi, T. Frauenheim, and S.-C. Zhang, EPL 90, 37002 (2010). [3] T. Sato, K. Segawa, H. Guo, K. Sugawara, S. Souma, T. Takahashi, and Y. Ando, Phys. Rev. Lett. 105, 136802 (2010). [4] Y. Chen, Z. Liu, J. G. Analytis, J.-H. Chu, H. Zhang, S.-K. Mo, R. G. Moore, D. Lu, I. Fisher, S. Zhang, Z. Hussain, and Z.-X. Shen, Phys. Rev. Lett. 105, 266401 (2010). [5] Su-Yang Xu, Y. Xia, L. A. Wray, S. Jia, F. Meier, J. H. Dil, J. Osterwalder, B. Slomski, A. Bansil, H. Lin, R. J. Cava, and M. Z. Hasan, Science 332, 560(2011).

Binary sesquichalcogenide materials such as bismuth selenide (Bi2Se3), antimony telluride (Sb2Te3), and bismuth telluride (Bi2Te3) are three-dimensional (3-D) topological insulators (TIs) having energy band-gap in the bulk and nontrivial conductive surface states. The unique phenomena of the topologically-protected surface states include a single Dirac cone in the E-k dispersion diagram, massless Dirac Fermions, and helical spin-momentum locking at or above room temperature. Because of these unique behaviors, the surface state of three-dimensional TIs is of considerable scientific and technological interests, offering the possibilities towards low-dissipation electronics, quantum computing, and manipulation of electro-magnetic interactions at nanoscale. However, exploiting the TI surface states remains a challenge, as the typically narrow band-gap in the bulk material leads to considerable conduction at room temperature, which overwhelms the contribution from surface states in transport measurements. Large surface-to-volume ratio and large bulk band-gap are highly desirable to reduce bulk conduction. Ultra-thin Bi2Se3 nanoplates and nanoribbons were grown employing chemical vapor deposition process under the vapor-solid mechanism. The closely-packed hexagonal crystalline structure and the chemical composition of the n-type doped nanoplates and nanoribbons have been confirmed with Raman Spectroscopy, Atomic Force Microscopy, Scanning Electron Microscopy, Transmission Electron Microscopy, and Electrical Characterization. The surface-area-to-volume ratios of the synthesized nanoplates and nanoribbons are as high as 0.17 m^-1 and 0.38 m^-1 for nanoplate and nanoribbon, respectively, making surface-rich topological insulator with reduced bulk density of states. A Bi2Se3 nanoplate-channel field-effect transistor was characterized, showing time-dependent conduction degradation in ambient condition.

Linear magnetoresistance (LMR) and weak anti-localization (WAL) have been observed to coexist in Bi chalocogenide topological insulators. It has been suggested that the LMR arises as a result of the linear band dispersion according to the Abrikosov model, while the WAL is known to be consequence of the strong spin orbit interactions and possibly the helicity of the surface states. However, various assumptions in the Abrikosov model cannot be well satisfied in experiments, such as the assumption that only the lowest Landau level electrons participate in the transport. We report the observation of WAL and LMR in epitaxial thin films of Bi₂Te₂Se with a carrier density of 5x10¹⁹ cm^-3. We provide a unified description of the two phenomena (LMR and WAL) using a modified Hikami-Larkin-Nagaoka (HLN) model. The logarithmic high-field trend of the HLN model is compensated by a parabola, thus resulting in a linear-like intermediate behavior versus magnetic field. The parabolic contribution can be a consequence of cyclotronic MR in the bulk or the result of a spin-orbit scattering channel in the low-field limit of the HLN model. Nevertheless, the WAL component dominates the MR to temperatures as high as T = 150 K and perhaps even to room temperature. This demonstrates that electrons retain phase coherence after many elastic scattering events even at high temperatures¹. Work supported by NSF-DMR-0907007 and NSF-DMR-0819762. JSM is partly supported by NSF-DMR 0504158 and ONR N00014-09-1-0177. ¹B.A. Assaf et al. arxiv: 1205.4635 ¹

We have developed a novel method for DNA sequencing based on the mechanical opening and closing of DNA hairpins geometry and the detection of roadblocks to re-hybridization due to the presence in solution of complementary fragments. Using a magnetic trap to pull on DNA tethered small magnetic beads, the position of the roadblocks on single molecules can be detected with nanometer precision which is sufficient to sequence DNA by hybridization or by ligation. The technique is simple, PCR-free, single molecule with low error rate, low cost (no fluorescently labeled nucleotides) and potentially high throughput.

Recent experiments have illuminated a remarkable growth mechanism of rod-shaped bacteria: proteins associated with cell wall extension move at constant velocity in circles oriented approximately along the cell circumference [Garner et al., Science (2011), Domínguez-Escobar et al. Science (2011), van Teeffelen et al. PNAS (2011)]. We view these as dislocations in the partially ordered peptidoglycan structure, activated by glycan strand extension machinery, and study theoretically the dynamics of these interacting defects on the surface of a cylinder. Generation and motion of these interacting defects lead to surprising effects arising from the cylindrical geometry, with important implications for growth. We also discuss how long range elastic interactions and turgor pressure affect the dynamics of the fraction of actively moving dislocations in the bacterial cell wall.

We present a simple model [1] for the thermomechanical behavior of homogeneous DNA at thermal equilibrium which is based only on the relevant symmetries. We predict critical temperatures for denaturation under torque and stretch, phase diagrams for stable B-DNA, supercoiling, optimally stable torque, and the overstretching transition as force-induced DNA melting. Agreement with available single molecule manipulation experiments is quite excellent. [1] Phys Rev Lett. 2011 Aug 5;107(6):068102.

Biological systems serve as great models for materials sciences as they demonstrate extraordinary control and precision in producing a wide range of biomaterials. One key discovery that empowers such controlled and reproducible synthesis was the revelation that a set combination of three DNA nucleotides as genetic codes that permitted the synthesis of proteins of a well-defined sequence and subsequent template synthesis of biomaterials. DNA has been increasingly recognized as a nanomaterial for its programmability and selective recognition properties, and thereby attracting great focus on post-functionalizing nanomaterials with DNA for various applications. Although the use of DNA in nanomaterial synthesis, such as formation of silver clusters and quantum dots have indicated an influence of DNA sequence on the morphology, structure and properties of the nanomaterial, few comprehensive or systematic study have been performed on the influence of various sequence in directing the growth of nanomaterials. Herein we report discovery of a different combination of DNA as genetic codes for fine control of the shape and morphology of gold nanoparticles during their synthesis using gold nanoprisms as seeds. Based on a detailed study of DNA guided synthesis, a set of rules that govern morphological growth of gold nanoparticles by DNA into a variety of novel shapes has been elucidated. Poly A30, poly T30, poly C30, or poly G20 was first investigated and were found to form rough round nanoplates, six-pointed nanostars, round smooth nanoplates and hexagonal nanoplates, respectively. The kinetics of these growths was traced by UV-vis absorption and the time-dependent shape evolution was investigated by quenching the reaction and observed under the TEM. To provide a more in depth study, DNA strands of two different deoxynucleobase with various segment lengths (i.e. T10G20, T15G15, T20G10 for the TG combination) were also investigated. In the two base system, the effect of A and C resulted in a rounder shape and rougher surface, whereas influence of T resulted in a six-pointed star shape and a smoother surface, and G resulted in a hexagonal shape and flattens the surface. Two interplaying effects, competitive and synergistic effect, were observed on the resulting particle when various permutations of the two-base DNA sequences were used. With this detailed study of DNA encoded nanoparticle synthesis, we sucessfully elucidated a set of relationships and guidelines to form various nanoparticle shapes and morphology by merely changing the DNA sequence used in the synthesis, mimicking the case of genetic coding in biomolecular synthesis. This study would provide a predictable method to synthesize novel nanoparticle structures which are important in a widespread of applications.

We discuss the rocirc;le of geometry, especially curvature in quantum mechanics of surfaces and thin tubes and thin rods. The interplay between elasticity and quantum mechanics is demonstrated by the propagation of a conformons along a thin ellastic rod that may model the DNA. Finally we are discussing the geometrical origins of the anticentrifugal force in 2D and possible applications.

Diatoms, bone, nacre and deep-sea sponges are mineralized natural structures found abundantly in nature. They exhibit mechanical properties on par with advanced engineering materials, yet their fundamental building blocks are brittle and weak. An intriguing characteristic of these structures is their heterogeneous distribution of mechanical properties. Specifically, diatoms exhibit nanoscale porosity in specific geometrical configurations to create regions with distinct stress strain responses, notably based on a single and simple building block, silica. The study reported here focuses on the mechanics and deformation mechanisms of silica-based nanocomposites with distinct topologies inspired by mineralized structures. We examine single edged notched tensile specimens and analyze stress and strain fields under varied sample size in order to gain fundamental insights into the deformation mechanisms of structures with distinct ordered arrangements of soft and stiff phases. Further, we investigate, both computationally and experimentally, the possibilities of functionalizing the composites by introducing phases with switchable mechanical properties, thus creating functional nano- and micromaterials with mutable fracture properties. We find that specific topological configurations of hierarchical arrangements of silica nanostructures markedly change the stress and strain transfer in the samples given appropriate elastic properties of the respective phases. The combined action of strain transfer in a deformable phase, and stress transfer in a stronger and stiffer phase, acts synergistically to reduce the intensity of stress concentrations around a crack tip, and renders the resulting composites less sensitive to the presence of flaws, certain geometrical arrangements even induces stable failure of the composites. Additionally, tailoring of elastic properties of the respective phases creates functional bioinspired materials with switchable mechanical properties. A systematic study allows us to identify composite structures with superior fracture mechanical properties relative to their constituents, akin to many natural biomineralized materials that turn the weaknesses of building blocks into a strength of the overall system.

One dimensional nanostructures are very interesting class of nanomaterials that has gained a lot of scientific interest recently. The electron conductivity along the long axis makes One dimensional nanostructures as a potential candidate for ballistic electron transfer. Also One dimensional nanostructures can help us better understand the effect of size confinement upon electrical, magnetic, optical and mechanical properties of materials. Tellurides have received a lot of attention recently since some of their properties like electrical and magnetic properties are enhanced due to quantum confinement. Tellurium nanowires are potential candidate for fabricating nanodevices. The reactivity of Tellurium nanowires with nanoparticles in the presence of biomolecules is new. In this research, the reactivity of Tellurium nanowires with gold in the presence of BSA is studied. Tellurium nanowires of length 700 nm and width 20nm was synthesized by reducing Tellurium in the presence of hydrazine hydrate. These nanowires were dispersed in water and then dried. The powder containing the nanowires was included in solution containing HAuCl4 to which NaOH was later added. It was observed that gold nanoparticles of uniform sizes were formed on the Tellurium nanowires. Also, when the Tellurium nanowires was added to solutions containing BSA and HAuCl4 to which NaOH was later added, it was observed that several nanowires were bent. It was observed that the morphology of the Tellurium nanowires depended upon factors such as the concentration of NaOH used for the reduction of gold. Various characterization tools such as TEM, XRD, Raman, UV-vis and photoluminescence measurements were used for understanding the interaction of Tellurium nanowires with gold. The formation of these Tellurium nanostructures is attributed to the combined effects of redox reactions and Nanoscale Kirkendall effect. This research has potential applications in the field of sensors.

Many natural and artificial microstructures, ranging from the outer walls of cells and pollen grains to polymeric microcapsules, are modeled as shells, i.e. thin elastic structures which are curved in their undeformed state. The mechanics of shells combines elasticity theory with principles of geometry and curvature. Because of the underlying curvature, it is impossible to bend any part of a shell without stretching it as well. This coupling between bending and stretching largely determines the response of shells to external forces and pressures. However, when the thickness of a shell goes down to a few nanometers, it becomes floppy enough to exhibit thermally generated deformations, which also strongly affect its elastic behaviour. Here, we study the effects of thermal fluctuations on the elastic properties of spherical shells through theoretical methods and Monte Carlo simulations. We found that fluctuations modify the response of the shell to point-like indentations and to external pressure, with contributions that increase both with temperature and with the ratio of shell radius to thickness. Thermal effects are also boosted by a large external pressure, and in fact diverge as the pressure approaches the classical buckling transition of the shell. We predict new phenomena that should be observable in experiments on shells with nanoscale thicknesses. Our results could also have implications for correctly interpreting atomic force microscope indentation and osmotic pressure buckling experiments that are routinely used to probe the mechanical properties of such structures.

We report on the translocation characteristics of molecular conjugates formed by ssDNA or protein wrapped single-walled carbons (SWNTs) through a capillary nanopore. Four molecular conjugates of different physical sizes and surface properties have been studied at the single-molecule level. Combining with optical spectroscopy, atomic force microscopy, and zeta-sizing technique, we find that the translocation time of a conjugate is determined by its hydrodynamic size and solution mobility. The translocation is rapid, in the order of tens of microsecond, as opposed to the millisecond timescale observed for biomolecules of similar hydrodynamic sizes. The current blockage reveal the effects of ion exclusion by the rod-shaped conjugate. Temporary polarization of the SWNT core of conjugate may effectively induce a second component in the change of event current during translocation. Together, the event current characteristics provide information about the diameter of the conjugate, and the conductivity nature of the SWNT core. The biomolecule-wrapped SWNTs represent a class of inorganic/ organic hybrid which behave very differently from the widely-researched organic molecules. Our study is hoped to bring new avenues in understanding the transport of generic inorganic/ organic hybrids through pore-like structures, of which process holds central importance in the applications of these hybrids in drug delivery, virus-based photovoltaic and bio-sensing.

Various triply periodic surfaces are in use to model interfaces. Favourite mathematical models include minimal surfaces, constant mean curvature surfaces, as well as surfaces minimizing bending or Helfrich energies, perhaps under a volume constraint. Skeletal graphs have been used to generate such surfaces or to capture their symmetries, but their definition has been somewhat obscur. After discussing the families of the above model surfaces I will present some recent results on skeletal graphs and their relationship to Steiner trees in 3-dimensional space. I will also give a characterization of the gyroid skeletal graph.

Surface plasmon resonances of metallic nanostructures can be utilized to tailor electromagnetic fields and the precise spatial arrangement of such structures can result in surprising optical properties that are not found in naturally occurring materials. These properties emerge from the collective action of single components, which only have limited individual functionality. Top-down fabrication of plasmonic materials with designed optical response in the visible range by conventional lithographic methods has remained challenging due to limited spatial resolution, the complexity of scaling, and the difficulty to generate three-dimensional architectures. Bottom-up molecular self-assembly provides an alternative route to create nanomaterials which is not restricted by the above limitations. We here demonstrate the fabrication of chiral self-assembled nanoscopic materials that possess tailored optical activity in the visible range. With 3D DNA origami, we arranged plasmonic nanoparticles into nanoscale helices with a spatial accuracy below 2 nm. As designed optical responses, we generated strong circular dichroism (CD) and optical rotatory dispersion (ORD) in the visible range originating from the collective plasmon-plasmon interactions within the nanohelices. We also show that the optical response can be spectrally tuned by changing the composition of the metal NPs. The observed effects are independent of the propagation direction of the incident light and are switchable by design between left- and right-handed orientations.

The brilliant, iridescent body colors of many beetles, butterflies, fish and birds are due to (coherent) scattering of light by nanostructured materials present in the integument that act as biological photonic crystals [1,2]. The refractive index of the biological structures is periodically modulated on the length scale of visible light (i.e. of the order of ~200 nm) with spatial variations in one, two or three dimensions. Of extreme interest are three-dimensional photonic crystals that mostly form one of the three simplest, triply-periodic, bicontinuous-cubic minimal surfaces: primitive cubic (P), diamond (D) or gyroid (G) [3]. Evolution has shaped the structures in a way that their reflectance is nearly optimal [4]. A most intriguing animal is the Neotropical diamond weevil, Entimus imperialis. By electron microscopy, we found that the weevil's body colors are created by randomly oriented, diamond-type photonic crystals, which exist inside scales that cover the hardened forewings, the elytra. The crystals appeared to have an fcc-symmetry. Using a hemispherical, imaging scatterometer, we were able to directly visualize the Brillouin zones of the photonic crystals [5]. The structural, minimal-symmetry representations are directly discernible in the hemispherical image. We were furthermore able to measure the directional reflectance spectra of the differently oriented crystals, which allowed the precise characterization of the photonic bandgap diagram of the crystals and thus the determination of the crystal orientation in the scales. The unique possibility of direct imaging of the Brillouin zones provides key insights not only for artificial mimicking photonic crystal structures, but also for non-invasive determination of unknown photonic structures encountered in other animals. We will discuss the implications of the biological signal created by the special scale arrangement of E. imperialis [6] and relate its photonics to that of other weevils. References [1] J. D. Joannopoulos, Photonic crystals: molding the flow of light (Princeton University Press, Princeton, 2008). [2] L. P. Biroacute; and J. Vigneron, Laser Photon. Rev.5, 27 (2011). [3] K. Michielsen and D. G. Stavenga, J. R. Soc. Interface5, 85 (2008). [4] P. Vukusic and J. R. Sambles, Nature424, 852 (2003). [5] B. D. Wilts et al., J. R. Soc. Interface9, 1609 (2012). [6] B. D. Wilts et al., Proc. R. Soc. B279, 2524 (2012).

We find that 48/64 hard spheres per unit cell on the gyroid minimal surface are entropically self-organized. Striking evidence is obtained in terms of the acceptance ratio of Monte Carlo moves and order parameters. The regular tessellations of the spheres can be viewed as hyperbolic tilings on the Poincare disc with a negative Gaussian curvature, one of which is, equivalently, the arrangement of angels and devils in Escher&’s Circle Limit IV. [1] T. Dotera, M. Kimoto and J. Matsuzawa, Interface Focus, doi:10.1098/rsfs.2011.0092

Cd_3Cu_4 has 1124 atoms in it unit cell, Al_55.4Cu_5.4Ta_39.1 has 23256 atoms and then there are the quasi-crystals. All these structures can be related to one another using a simple albeit higher dimensional geometry, a concept from 4-D Platonic solids. These structures in four dimensions are topologically similar. The model at its best, for group 10 to 12 inter-metallics, can rationalize a great deal about their stoichiometry and their numbers of valence electrons per atom.

In this work we discuss the nature and evolution of dealloying and porosity evolution in binary alloy, metallic nanoparticles via kinetic Monte Carlo simulations. Dealloying is a nanoscale processing tool used to fabricate high surface area materials. Through our simulations we have identified several key differences in porosity evolution between bulk and nanoparticle samples. Unlike the bulk case, the critical potential is not a sharp threshold separating porosity evolution from passivation. Instead, we find a potential dependence on the propensity for porosity evolution and define the critical potential when we have equal distributions of passivated and dealloyed particles. Most notably, in this work we observed that the potential for porosity evolution in nanoparticles is more positive than required for porosity evolution in bulk materials, and increases with decreasing particle size. This is a manifestation of a Gibbs-Thomson effect, but appears to be have an inverse dependence due to our unique case of a binary alloy, metallic nanoparticle. As the particle size decreases, akin to the elemental nanoparticle case, the lesser noble component is more easily stripped away from the surface of nanoparticle. As a result the nanoparticles form more noble component passivated surfaces, and porosity evolution in nanoparticles can only evolve if fluctuations in the surface passivated layer are long-lived enough to allow dissolution from the bulk of the nanoparticle. In following with the Gibbs-Thomson effect surface fluctuations are shorter lived with smaller particle sizes, which necessitate an increase in the applied potential in order to form a porous particle.

Gold, usually known for its inertness, can be prepared as a nanoporous bulk material showing catalytic properties. A particular advantage of this catalytic material is the stable monolithic structure, combining mechanical strength, thermal and electrical conductivity and a reproducible porosity due to self-organization during the preparation by corrosion (leaching of Ag in an Ag-rich AuAg alloy). This is leading to many possible applications e.g. in catalysts, sensors and electrode materials. Important structural properties are the pore size and the size of the gold ligaments. TEM (transmission electron microscopy) is a powerful tool to obtain information on these properties. While for semiconductor structures the information obtained by the projections made in TEM may be sufficient, in the case of nanoporous gold, information on the three-dimensional structure is required. Therefore STEM- (scanning TEM) tomography is applied, which allows reconstruction of the three-dimensional structure of an object, if many projections are taken under different angles. The preparation of the porous gold was tested with focused ion beam - preparation, conventional preparation of nanoporous gold embedded in epoxy and ultramicrotome preparation of nanoporous gold embedded in epoxy. Considering the beam damage on the structure and the contamination of the surface, ultramicrotome preparation turned out to be the best solution. Slices of the porous gold were cut with thicknesses of 50 nm and 100 nm. With decreasing specimen thickness, the resolution of the tomographic reconstruction improves. On the other hand, a minimum thickness is necessary to have a representative three-dimensional structure, which means the choice of specimen thickness is a trade-off. A tilt series was acquired in 2° steps from -70° to + 70° with an FEI Titan 80/300 TEM. The three dimensional structure of the nanoporous gold was reconstructed with the weighted backprojection method and with the SIRT-method, using the program Inspect3D from FEI. Additionally, we studied the functionalization of the nanoporous gold with TiO₂ particles. For the application in catalysis of CO-oxidation, the gold can be coated with TiO₂ in order to enhance catalytic activity. In the temperature range above 60 °C the CO conversion of the TiO₂ coated sample is increased by more than one order of magnitude compared with the pure nanoporous gold. Structure and distribution of the TiO₂ on the gold surface is an important property, which was investigated by TEM. It was shown, that the gold ligaments are abundantly covered by approximately 5 nm TiO₂ particles. The determination of the largest lattice fringe distance with high resolution TEM revealed that the crystalline nanoparticles consist of the anatase phase. The spatial Ti distribution was measured with energy filtered TEM. STEM-Tomography was also used to reconstruct the three-dimensional structure of the TiO₂ particles.

Recently, nonspherical gold nanoparticles have become the focus of this field because the optical and electronic properties of NPs are not only size-dependent but also shape-dependent. In present study, we reported a simple and facile approach was employed to synthesis spherical and urchin-like gold-coated iron oxide nanoparticle (Fe3O4@Au NP). Fe3O4 nanoparticles are used as the central core to prepare Fe3O4@Au in aqueous state without precipitation and aggregation of nanoparticles. Citrate coated Fe3O4 nanoparticles are initially prepared and subsequently coated with Au layers under citrate of Fe3O4 surface reduction of HAuCl4; and then synthesize urchin-like Fe3O4@Au NP in the presence of hydroquinone through a seed-mediated growth approach. By altering the feed ratio of seeds and hydroquinone, the diameters of urchin-like NPs were tunable. Accordingly, the centers of surface plasmon resonance absorption shifted from 600 to 670 nm. The properties of Fe3O4@Au nanoparticles were extensively characterized with transmission electron microscopy (TEM), atomic force microscope (AFM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX), UV/Vis absorption spectroscopy, fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA) and zeta-potential methods presented excellent homogeneity with the average diameter and high dispersity at all ranges of pH with long term stability. These nanoparticles can be used in biomedical applications including drug delivery; separation, and purification of biomolecules from the matrices.