Symposium SM07—Building Advanced Materials by Self-Assembly

Heterogeneous distributions of ions and water at interfaces have a strong impact on processes of nucleation and assembly. This talk will introduce how to investigate these phenomena and their relationship to interfacial structure for a number of mineral systems in aqueous electrolyte solutions via using a combination of in situ imaging techniques such as in situ liquid cell atomic force microscopy (AFM) and in situ liquid phase scanning/transmission electron microscopy (S/TEM) and computational methods.

Nanocrystals have attracted considerable attention because of their potential applications in catalysis, energy storage, microelectronic devices, biomedicines, etc. Monodisperse nanocrystals could form superlattices with emergent collective properties. Although there have been intensive studies on nanocrystal superlattices, how individual nanocrystals change and how they interact with each other during superlattice transformations are unclear. Direct observation with high spatial and temporal resolution using transmission electron microscopy (TEM) provides the opportunity to address these questions. This talk will introduce the development of high-resolution carbon-film liquid cells, which allow to directly observe nanocrystal superlattice transitions using TEM.

Nanocrystal materials are emerging as an important class of tools that are revolutionizing both fundamental science and technological applications due to their many unique properties. In particular, quantum dots nanocrystals have demonstrated their great potential to be applied in a wide variety of applications as a unique emissive material. In my talk, I will describe our experimental efforts for the synthesis and characterization of high-quality quantum dot nanocrystals. These dots combine, in one material, great optical performance metrics desired in quantum dot nanomaterials. Then, I will show how we can use colloidal quantum dot nanocrystals as building blocks to generate higher-order architectures in assemblies. At last, several quantum dot based applications studied in my lab will be discussed.

This talk will summarize recent progress on the studies of pressure Induced nanoparticle aggregation behavior. This talk starts with a brief overview of high pressure characterization techniques, coupled with synchrotron X-ray scattering, Raman, fluorescence, and absorption. Then, the pressure Induced nanoparticle aggregation behavior including size dependent aggregation and threshold pressures using several typical NP material systems as examples. Finally, outlooks with future directions are discussed.

Nanoparticle superstructures are versatile materials platforms for fundamental study of colloidal assembly and exploration of technologically relevant applications. In this talk, I will describe our recent progress on kinetically controlled assembly of multicomponent superstructures using spherical nanoparticles with tunable softness. Characterization of kinetically arrested intermediates reveals a multistep crystallization pathway defying the classical nucleation theory. Next, I will present our work on assemblies of shape-anisotropic nanoparticles with tunable softness. The interplay between particle shape and interaction softness leads to rich phase behaviors.

The oriented attachment of molecular clusters and nanoparticles in solution is now recognized as an important mechanism of crystal growth in many materials. This talk will introduce the background of oriented attachment and the application of high-resolution fluid cell transmission electron microscopy (TEM) to directly observe oriented attachment of several nanoparticle systems, including iron oxyhydroxids, Au, Ag, and Pt.

Molecular or atomistic mechanistic understanding of nucleation, growth, and structural changes of nanoparticles have not achieved enough at the nanoscale or below. It is mainly because of a lack of appropriate analytical methods that can obtain in-situ structural information with a spatial resolution at such small length scale along with sub-msec temporal resolution. The in situ, both in liquid phase and dry state, transmission electron microscopy (TEM) offers an opportunity to directly observe diverse classes of chemical reactions. Here we introduce technical developments for those techniques. Topics will cover fabrication processes for TEM liquid cells with thin film window materials such as graphene and silicon nitride, and data processing of large sized in situ TEM images. In addition, we also present application of in situ TEM to study chemistry of colloidal nanoparticles. We reveal that the early stage of nanoparticle formation is driven by reversible transition between disordered and ordered phases before crystalline phase is stable above a certain size. It is also frequently observed that different types of non-classical pathway, including two-step nucleation, amorphous-to-crystalline transition, and coalescence of clusters, are heavily involved in different conditions of nanoparticle formation. We also present a new development using liquid phase TEM to investigate 3D atomic structures of nanoparticles directly in the colloidal synthesis batch.

Understanding how materials form at the nanoscale is fundamental for materials engineering and fabrication in many functional nanodevices. Nucleation, growth, and self-assembly are key “bottom-up” processes through which these materials form in solution. Despite the importance of these processes both from basic science principles and technological stand-point, many of the chemical and physical details of these dynamic processes remain unknown. This gap in knowledge stems mainly from a lack of proper experimental techniques that enables visualize these nanoscale solution-based processes in real-time. Here, using in situ liquid cell transmission electron microscopy (TEM), I will describe how direct observations can shed new light on nucleation and growth of both organic and inorganic crystals.
Specifically, I will show that organic crystals such as metal-organic frameworks nucleate via a nonclassical pathway, involving phase separation of the precursor solution into dense solute-rich and solute poor-regions, followed by condensation of the dense phase into crystals. I will also discuss the nucleation and crystallization of other organic materials such as perovskites and illustrate that visualizing these crystallization pathways can teach us a lot in terms of materials synthesis.
Our studies highlight the importance of direct visualization of nanoscale processes for the rational design of materials.

Many materials properties are determined through their underlying crystal structure, and often the search for new materials with improved functionalities requires the targeting of particular structure types and crystal geometries. While the science of crystallography has helped us to largely decipher the structure of materials over the past century, the art of structure prediction has remained elusive: our ability to rationalize why a certain system crystallizes in any given structure is severely constrained, for example by being applicable to only specific materials classes or by being predictive of ground-state structures without allowing to draw conclusions about the aspect of synthesizability.

We investigate the enigma of crystal structure formation by simulating the growth of different crystal phases from particles with exquisitely simple interactions. By modeling the self-assembly of long-range ordered structures with varying complexity and symmetry, we aim to formulate the general principles of the development of crystallinity from local interactions. We hope to elucidate how complexity can emerge from simple particles, how long-range order emerges from short-range forces, and how symmetries are broken locally in concert with the appearance of global, crystal symmetries.

By developing a fundamental understanding of the process of self-assembly in crystalline matter, we can move forward with efforts of structure prediction at a level that will enable materials design from basic principles in the future.

Quasicrystals are structures that are ordered but not periodic. While they lack translational symmetry, they possess a high degree of rotational symmetry. Their experimental identification in 1984 brought the concept of aperiodic structures from mathematical tilings to physical existence. Since then, the experimental pursuit of these elusive materials has extended from atomic systems to colloidal superlattices. To date, all experimentally reported quasicrystalline superlattices possess either multiple sizes or the asymmetric functionalization of building blocks. The question of whether it is possible to synthetically achieve quasicrystals using one uniformly functionalized constituent remains elusive. Utilizing five-fold symmetric nanocrystals and elastically directional, oligonucleotide-based ligands, we report the first single-component dodecagonal colloidal quasicrystal assembled from DNA-functionalized decahedral nanocrystals. This discovery enriches the scope of colloidal quasicrystals, and sheds light on the design-based, enthalpy-driven crystallization of polyhedral nanocrystals.

The localized surface plasmon resonance of metallic nanoparticles continues to be studied for light harvesting applications such as photocatalysis and biosensing. Control over the light response depends on careful synthetic control of the particle structure, composition, and state of assembly. Whereas the current theoretical understanding of nanoparticle growth has been sufficient for enabling the synthesis of monodisperse spherical nanoparticles, shortcomings in current theories hinder the prediction of synthetic outcomes in more complex experimental systems (e.g. non-spherical morphologies, particle superstructures). An underlying challenge which we seek to address is the development of methodologies for connecting large experimental design spaces to the outcomes of nanoparticle syntheses that may also span over multiple length and time scales. Herein, we present a multivariate analysis of how amphiphilic solid binding peptides can mediate the nucleation, growth, morphogenesis, and self-assembly of gold nanoparticles over a broad range of conditions. High-throughput synthesis using programable liquid-handling robots is coupled with UV-Vis characterization to create state diagrams for visualizing the relationship between surface plasmon resonance or colloidal stability, and sample composition and peptide sequence. We then demonstrate the utility of unsupervised learning techniques to identify these relationships and for guiding selection of samples for lower-throughput characterization techniques. The structure of selected samples is investigated further using transmission electron microscopy (TEM) and small angle x-ray scattering (SAXS). Together, these results motivate targeted in situ experiments which reveal how peptide self-assembly and complexation with precursors lead to distinct modes of growth and self-assembly. Finally, we discuss how these methodologies can also be extended to the study of other hybrid inorganic-organic systems that are driven by nucleation and growth phenomena.

The early observation of strong circular dichroism for individual nanoparticles (NPs) and their assemblies have developed into a rapidly expanding field of chiral inorganic nanostructures. They encompass a large family of mirror-asymmetric constructs from metals, semiconductors, ceramics, and nanocarbons with multiple chiral geometries with characteristic scales from Ångströms to microns. Versatility in dimensions and polarizability of the inorganic materials enables their multiscale engineering to attain a broad range of optical and chemical properties. This talk will address (1) the origin of the uniquely high values of optical anisotropy; (2) mechanisms of chirality transfer in inorganic materials; and (3) emergence of complexity is self-organized chiral nanoassemblies. Special attention will be given to the emerging venues for practical realizations of chiral nanoassemblies related to (1) chiral catalysis and (2) circular polarization spectroscopy in terahertz spectral window.

References
W. Jiang, Z.-B. Qu, P. Kumar, D. Vecchio, Y. Wang, Y. Ma, J. H. Bahng, K.Bernardino, W. R. Gomes, F. M. Colombari, A. Lozada-Blanco, M. Veksler, E. Marino, A. Simon, C. Murray, S. Ricardo Muniz, A. F. de Moura, N. A. Kotov, Emergence of Complexity in Hierarchically Organized Chiral Particles, Science, 2020, 368, 6491, 642-648.

Si Li, Juan Liu, Naomi S. Ramesar, Hendrik Heinz, Liguang Xu, Chuanlai Xu, Nicholas A. Kotov, Single- and Multi-Component Chiral Supraparticles As Modular Enantioselective Catalysts, Nature Comm, 2019, 10, 4826.

W.J. Choi, G. Cheng, Z. Huang, S. Zhang, T. B. Norris, N. A. Kotov, Chiroptical Kirigami Modulators for Terahertz Circular Dichroism Spectroscopy of Biomaterials, Nature Materials, 2019, 18, 820–826.

Previous studies have demonstrated chemical fuel driven dissipative self-assembly of colloids initiated by adding a chemical fuel that converts hydrophilic surface groups to hydrophobic groups. The hydrophobic colloids aggregate over several hours while a slow hydrolysis back reaction converts hydrophobic groups back to hydrophilic, causing the aggregates to disassemble after tens of hours. While the chemical reactions involved in dissipative self-assembly process have been studied in detail, the colloidal scale interparticle interactions underlying self-assembly are not well understood. Here we demonstrate that the dissipative self-assembly of carboxylic acid functionalized polystyrene occurs over narrow ranges of fuel and particle concentrations that are dictated by the strength of hydrophobic interparticle interactions and the ligand-fuel reaction kinetics. We utilized optical microscopy to image dissipative self-assembly of sub-micron to micron sized particles to probe assembly behavior as a function of particle and fuel concentration. Particles showed either no assembly, dissipative self-assembly, or irreversible aggregation. A scaling analysis revealed that no assembly occurred if the lifetime of the surface hydrophobic groups was less than the characteristic time for colloidal aggregation as determined by the Fuch’s stability parameter. Dissipative assembly occurred for fuel concentrations where there was a secondary minimum in the pairwise interaction potential, which lead to weak hydrophobic interparticle bonds and residual interstitial water layers that facilitated hydrolysis back reactions. Irreversible assembly occurred when hydrophobic attractive forces dominated electrostatic repulsion and caused permanent aggregation with no residual interstitial water layer. These results shed light on the interplay between colloidal interactions and kinetics that underly dissipative self-assembly of colloids and will enable rational design of transient and reconfigurable colloid assemblies.

Nanocrystals of different functional materials can self-assemble from colloidal solutions into long-range ordered periodic and quasicrystalline structures (superlattices). Such assemblies offer a powerful platform for designing hierarchically organized macroscopic solids. Unlike atomic and molecular crystals where atoms, lattice geometry, and interatomic distances are fixed entities, arrays of nanocrystals represent solids made of “designer atoms” with potential for continuous tuning their physical and chemical properties. The self-assembly process is guided by an intricate interplay of entropy-driven crystallization and soft interparticle interactions. The surface ligands also play an important and sometimes counterintuitive role, supporting many-body interactions and stabilizing complex structures which can be explained by specific topological textures developed within surface ligands.
The properties of nanocrystal superlattices are determined by the nanocrystalline building blocks and by the electronic couplings between individual nanocrystals. Strong electronic coupling between nanocrystals within a superlattice is an important prerequisite for the emergence of non-additive physical properties. By using optimized surface chemistries, the electronic coupling can be significantly enhanced, approaching the metal-insulator transition. The formation of strongly-coupled nanocrystal assemblies represents an important step toward the bottom-up design of functional materials. We will demonstrate the power of “modular” materials fabrication for electronic and optoelectronic devices and the utility of engineered nanocrystal assemblies for real-world technologies.

Metal nanocrystals have gained tremendous attention due to their superior performance in various applications, ranging from selective catalysis to electronic devices to plasmonic applications. For these and many other applications, the properties of the nanocrystals are highly sensitive to their shape. However, it remains a challenge to achieve high shape selectivity in solution-phase syntheses. I will discuss our efforts to understand the growth of Cu and Ag nanocubes, nanowires and nanoplates, which is facilitated by a synergy between halide ions (chloride, bromide, and iodide) and capping molecules in the synthesis protocol. We use ab initio thermodynamics based on quantum density-functional theory (DFT) to demonstrate how the combination of capping molecules and halides create thermodynamic driving forces for cubes, plates and wires, by selectively altering surface energies. Using a combination of DFT and the theory of absorbing Markov chains, we demonstrate how a synergy between capping molecules and halides affect deposition, surface diffusion, and interfacet transport to drive the growth of particular nanoshapes. Our results agree with experiment and indicate a promising way to exact control over nanocrystal synthesis.

I will present our most recent experiment-computation collaboration on a new strategy of “atomic stencil” to site-specifically coat gold nanoparticles (NPs) with polymer patches. We experimentally demonstrate the general applicability of the strategy in patterning polymer patches of precise size and shapes on a variety of anisotropic gold NPs. We realize highly uniform patchy NPs, from tip to facet-patches, as well as from symmetric to broken-symmetry patch arrangements. The patch grafting simulation based on scaling theory reveals the vital roles of interpolymer attraction and local surface curvature of NPs in polymer portioning. Finally, we show that the as-prepared library of patchy NPs can assemble into various structures, including small clusters (dimers, trimers) via self-limited attraction, and large-scale open lattices, which are challenging to be achieved from NPs of uniform surface chemistry. We foresee the method can generate hybrid NPs with site-specifically programmable chemistries and interactions for the applications in catalytic, delivery, and their directed assembly into exotic functional structures, including a Kagome lattice.

Polymer-inorganic nanocomposites based on polymer-grafted nanocrystals (PGNCs) are enabling technologically relevant applications owing to their unique physical and chemical properties. While diverse PGNC superstructures have been realized through evaporation-driven self-assembly, this approach presents multifaceted challenges in understanding and ultimately ucontrolling the assembly kinetics. In this talk, I will introduce our recent progress on the facile assembly of multicomponent superstructures from a homogeneous disordered PGNC mixture. We demonstrate that controlling the nature of assembly environment allows for exquisite control of the rate of PGNC assembly. Characterization of kinetically arrested intermediates reveals that assembly follows a multistep crystallization pathway. Our work opens up new avenues for the predictive synthesis of multicomponent PGNC superstructures exhibiting mutlifunctionality and emergent properties.

Natural cellular materials have inspired researchers to created lightweight high-strength porous metals with chemical or physical functionalities. Traditional fabrication methods, however, have limited porous metals' strength to well below their theoretical limits because of the difficulties in controlling the pore morphology and the constituent metal's microstructure. 3D printing is one manufacturing technique that has realized nanolattices with periodic pores and nanostructures that approach the theoretical strength of their constituent materials [1], but it has inherent trade-offs between resolution and printing time that severely limit the scalability. In addition to 3D printing, advancements in self-assembly have realized relatively low cost and fast fabrication of large-area metallic and ceramic nanolattices with nanometer-sized features, but the assembled templates are subject to dense cracks unavoidable during solvent drying [2]. Filling the template voids with a solid material can fill the cracks, but these inverted crack structures divide the sample into small nanolattice domains (typically <0.01 mm² in area), cause stress concentrations, block fluid/gas transport, and increase optical scattering. A fabrication approach that uses self-assembled templates to produce large-area metallic nanolattices without inverted cracks has yet to be demonstrated.
This work overcomes these limitations by developing a crack-free colloid self-assembly approach to fabricate cm-scale porous nickel nanolattices with 30 nm grain size, 100 nm feature sizes, and an ultrahigh 227 MPa tensile strength, 3 times stronger than what has been reported for porous metals with the same relative density at any scale. We fabricate our nickel nanolattices by first self-assembling 400-800 nm diameter polystyrene (PS) particles with positive surface charges into single-crystalline FCC packed films on an indium tin oxide (ITO) coated substrate. We then electrodeposit nickel through the template voids and etch the PS by toluene. We found that the key to eliminating cracks in the colloid self-assembly process while maintaining high-quality crystal growth, which reduces defects and improves optical properties, is to keep the template wet with 0.06% glycerol. After self-assembly of a wet uncracked colloid template, we then overcame the challenge of electrodepositing nickel in a wet unsintered template by taking advantage of electroosmotic forces on synthesized positively charged polystyrene particles that push the template onto the conductive substrate. Compared to traditional self-assembly, the new approach overcomes the long-standing cracking issues in self-assembled colloid templates to fabricate nanolattices, which have over 2 cm² area without inverted cracks, 20,000X increase in crack-free area compared to conventional self-assembled metallic nanolattices, 1,000X more units cells in the loaded direction than 3D printed nanolattices for tensile testing, and, for the first time, enable macroscopic tensile testing of metallic nanolattices.

1. Bauer, J., et al., Nanolattices: An Emerging Class of Mechanical Metamaterials. Advanced Materials, 2017. 29(40): p. 1701850.
2. Jiang, Z., Z. Hsain, and J.H. Pikul, Thick Free-Standing Metallic Inverse Opals Enabled by New Insights into the Fracture of Drying Particle Films. Langmuir, 2020. 36(26): p. 7315-7324.

Centimeter-scale hydrophilic two-dimensional (2D) magnetic sheets are created via rapid self-assembly of magnetic nanoparticles at liquid-liquid interface. Such large-scale 2D sheets open up new avenue to engineering 2D materials. Assembly of nanoparticles at liquid interfaces has attracted much attention for decades. Yet, developing their assemblies of mechanically intact structure is comparatively few as most of assemblies collapsed when the interface is removed. Moreover, only a limited number of studies on the ability to form thin sheets with magnetic properties have been reported. In this context, our 2D magnetic thin sheets are structurally intact that retain the millimeter-scale continuity even after three times of centrifugation and washing with pure water, without additional crosslinking or polymerization processes. The formation of such mechanically robust sheets can be attributed to ligand interactions, hydrogen bonding, and favorable dipole-dipole interaction of magnetic nanoparticles. Furthermore, mechanical and magnetic properties of the 2D membrane are investigated. Finally, self-assembly is also carried out using magnetic nanoparticles of larger size distribution, demonstrating the versatility of this strategy for crafting 2D sheets.

Growth of single crystals via oriented attachment of primary nanocrystals is widespread phenomenon in both synthetic and natural environments. This process exhibits a range of styles including face-specific oriented attachment (OA) in which the primary particles and final crystal are of the same phase, attachment of a nanoscopic phase to a bulk phase followed by transformation to form a crystal with crystallographically matched or twinned interfaces, and mis-oriented aggregation followed by coarsening through elimination of dislocations to a single crystal. While descriptions of assembly in these systems must share a commonality with continuum-based DLVO-type theories for simple colloids, nanocrystals present additional complexities, including face-specificity of dielectric properties, surfaces that are periodically structured at the Å-scale structure, and consequent solvent-responses that are expected to be of a comparable length scale. To understand the relationship between nanocrystal and solution structure, interparticle forces and consequent motion leading to attachment, we are investigating oriented attachment in a number of crystal systems including ZnO, Fe₂O₃ and AlO(OH). We use in situ AFM to map the structure of both the crystal surface and the near surface solution, in situ TEM to observe assembly dynamics, force spectroscopy with custom-made single crystal tips to measure face-specific interparticle forces, and molecular-scale simulations to define the relationships between these features. AFM-based fast force mapping shows that the structure of the solution near the interface exhibits the symmetry of the underlying crystal with lateral variations in density on the same scale as the atomic lattice, but the extent of these variations away from the surface varies between crystal systems and with ionic strength. Moreover, measurements with different kinds of tips combined with molecular dynamic simulations show that the measured solvent structure is impacted by the probe chemistry, implying that, as particles approach, the structure of the solvent evolves in response to the changing interfacial chemical environment. In situ TEM demonstrates that direction-specific forces align randomly diffusing particles prior to contact and that attachment occurs on lattice matched faces via a sudden jump to contact followed by coarsening to produce compact single crystal structures. Direct measurements of the forces between crystal surfaces reveal orientation dependent attractive interactions that also exhibit the symmetry of the underlying lattice. Simulations show that orienting, attractive forces arise from a number of sources, including hydration, ion correlation and dispersion forces and barriers to attachment are caused by hydration layers, which vary with surface hydrophobicity. In at least one case — ZnO — electric dipole forces dominate the interparticle interactions and lead to coalignment long before contact occurs. The integration of these complimentary techniques and their application to multiple crystal systems is helping to provide a comprehensive physical picture of OA.

Nanoparticle self-assembly plays a key role in the formation of superlattices, which exhibit remarkable physical and chemical properties. However, controlling the assembly remains a challenge partly due to a lack of understanding of the assembly dynamics and the difficulty in linking interfacial solution properties to interparticle forces. Using liquid-cell transmission electron microscopy, the self-assembly of gold nanoparticles (NPs) into superlattices in mixtures of water and ionic liquid (IL) was visualized, revealing a dual role of the IL in the assembly process. At intermediate concentrations, the IL acts as a surfactant stabilizing the particles at a well-defined equilibrium separation corresponding to the length of hydrogen-bonded IL cations adsorbed onto neighboring NPs. Analysis of the interparticle forces reveals attractive long-range interactions of a van der Waals nature. At separations of 1−3 nm, the interactions are dominated by attractive ion correlation and repulsive hydration forces giving rise to an energy minimum at 1.5 nm separation. The superlattice is further stabilized by hydrogen bonding, which shifts the equilibrium interparticle distance to 1.1 nm. In contrast, at higher concentrations, IL accumulates and forms a structured network in the gap between nanoparticles, where it acts as a solvent that eliminates the repulsive barrier and thus promotes particle coalescence. This solvent−surfactant duality of IL opens new opportunities for its use in directing particle assembly.

We utilize nanoparticle dispersion as a model system to study the fundamentals of order emergence and evolution at the nanoscale. Diverse superlattices are achieved under liquid-phase TEM which enables single-particle level imaging in real time and real space. To be specific, coalescence and oriented attachment of two dimensional/three dimensional (2D/3D) superlattices are observed, where both attach–rotation and prealign–attach behaviors occur. Machine learning is used for the first time to extract the structural information in 3D superlattices, which further helps to identify single particle behaviors. Furthermore, the high spatiotemporal resolution enables us to identify single particles and to map out their trajectories sampling the energy landscape. The individual fast motion (e.g. surface and volume diffusion) along with collective motion (e.g. transient neck formation, translational and translational motion of the domains) drives the coarsening of the nanoparticle superlattice, which is attributed to the features of different interactions involved at the nanoscale. Our work proposes novel data acquisition protocol and offers new dynamic observations on the superlattice evolution with high spatial and temporal resolution, which can provide insight into material engineering at the nanoscale.

Corals reef ecosystems are extremely diverse, beautiful, and threatened by climate change. Learning how corals form their skeletons may be useful to save them from global warming, and to develop new synthesis strategies. Coral skeletons, in fact, are Nature’s 3D printing. Recent synchrotron spectromicroscopy data reveal that all reef-building coral build their skeletons by two concomitant mechanisms:
1. Particle attachment, with nanoparticles of amorphous precursors nucleated in the tissue
2. Ion attachment, at the surface of the growing skeleton, from the calcifying fluid.
A new model for coral skeleton formation shows both mechanisms. See Sun et al. PNAS 2020.

Understanding particle mediated growth is critical to geoscience, material synthesis, catalysis, energy storage, environmental conservation, biological medicine, etc. Using a combination of scanning/transmission electron microscopy (S/TEM), atomic force microscopy (AFM), small angle X-ray scattering (SAXS), and molecular computations, we are investigating these phenomena for several metal oxide systems and their relationship to interfacial structure in vacuum, water vapor, and solutions. Here we discuss two cases. In the first, we explore the aggregation behaviors of hematite nanocrystals with different exposed facets including {001}, {012}, {104} and {116} in aqueous solutions at room temperature or hydrothermal conditions (120-180 ^oC). SAXS was used to study the aggregation behavior at room temperature. Remarkably, only {104} nanoparticles are well mono-dispersed in aqueous solutions from 1 to 30 mg/ml at 10, 30, and 60 days. In contrast, at similar conditions 001} and {116} nanoparticles are highly aggregated. High resolution TEM and scanning TEM (STEM) on aggregates formed at hydrothermal conditions suggest hematite crystallization by nanoparticle aggregation occurs predominantly on [001] facets. We then compare the results to the predictions of coupled plane-wave and classical density functional theory simulations to relate the behavior to surface interactions. In the second case, we report measurement of anisotropic forces between rutile TiO₂ (001) nanocrystals as a function of their azimuthal orientation and surface hydration extent using a combined environmental TEM-atomic force microscopy (AFM) technique. At tens of nanometers of separation, the attractive forces are weak and show no dependence on azimuthal alignment nor surface hydration. At separations of approximately one hydration layer, attractive forces are strongly dependent on azimuthal alignment and systematically decrease as intervening water density increases. Measured forces closely agree with predictions from Lifshitz theory and show that dispersion forces are capable of generating a torque between particles to align them. Ongoing adaptation of these modeling techniques to explain the observed aggregation behavior in the hematite system are motivated by the need to ultimately uncover common underlying mechanisms driving particle-mediated crystallization phenomena such as oriented aggregation.

Compartments are essential for any life, cells, prokaryotes, and even viruses. Recreation of their formation has both technological and fundamental importance. This study shows that L-cysteine stabilized iron sulfide NPs can self-assemble into multi-compartment supraparticles (SPs). The transmission electron microscopy results showed that NPs initially produce ~55nm cup-like structures and then mature into ~75nm SPs with ca.190 interconnected compartments. The color change of the solution from black to yellow suggests the SP formation and particle oxidation. The selected area electron diffraction and energy dispersive X-ray spectroscopy confirm that SPs are formed from FeS₂ and Fe₂O₃ NPs. Elemental mapping showed that Fe₂O₃ NPs are located on the SP's surface and protecting FeS₂ and compartments from the surroundings. These compartmentalized particles can be used for the successful encapsulation of the DNA fragments and gene delivery.

Self-assemblies have attracted great scientific interests in recent few decades due to their various potential applications. Scientists can obtain different elaborate assemblies with multiple on-demand functionalities using various noncovalent interactions, such as hydrophilic-hydrophobic interaction, hydrogen bonding, host-guest interaction, π-π interaction, metal coordination, etc. Although the formation or responsive process of these assemblies can be monitored by various methods, such as NMR, IR, MS and electron microscopy, etc., a problem associated with these methods is that they are either invisible to our naked eye or rely on harsh preparation methods. Luminescence is a perfect choice as technique for the applications in self-assemblies, in the light of its rich advantages such as superior sensitivity, high selectivity, fast response, low background noise and simplicity. More importantly, it can provide high spatiotemporal resolution for precise visualization into complicated processes in a noninvasive and on-site way. Another thing that need to be considered is that most of the assemblies function in the condensed phase which show notoriously ACQ effect to result in compromised sensitivity. Diametrically opposed to conventional luminophores, AIEgens are nearly non-luminescent in the isolated state but luminesce strongly in the aggregate/clustered state. Based on different AIEgens, we have fabricated various functional self-assemblies, such as helical assemblies with circularly polarized luminescence signal, surfactant micelles and microemulsion droplets with visible transition processes, interfacial dynamic self-assembly with in situ imaging technology, supramolecular polymers formed from TPE-based luminescent monomer, etc.

General strategies leading to scale-span molecular self-assembly are of crucial importance in creating bulk supramolecular materials. We report that under mechanical pressure, caking of the precipitated molecular self-assemblies may lead to bulk supramolecular films. Massive fabrication of supramolecular films becomes possible using a simple house-hold noodle machine. The film can be endowed diversified functions by depositing various functional ingredients via co-precipitation. We expect the current work opens up a new paradigm leading to large-scale functional solid molecular self-assembled materials.

Dye-loaded fluorescent polymeric nanoparticles (NPs) appear as an attractive alternative to inorganic NPs, such as quantum dots (QDots).^[1] However, preparation of polymeric NPs featuring small size and high fluorescence brightness remains a challenge. To address it, we introduced a concept of charge-controlled nanoprecipitation of hydrophobic polymers in aqueous media.^[2] We found that a single charge in polymers, such as poly(methyl methacrylate) (PMMA), poly(lactic-co-glycolic acid) (PLGA) and polycaprolactone (PCL) can drive self-assembly of polymers into NPs of 20-40 nm size. Further addition of charges into these polymers (up to 10 mol%) can decrease particle size down to 7 nm.^[3] On the other hand, to ensure high brightness of polymeric NPs, we proposed to encapsulate charged dyes with bulky hydrophobic counterions.^[4] The later serve as spacers between dyes, thus preventing aggregation-cause quenching and, at the same time, favor the co-assembly of the dyes with the polymer into stable NPs without dye leakage.^[5] Based on these design concepts, we obtained NPs that are ~100-fold brighter than QDots of similar size.^[6] Their small size was found essential for their free diffusion in cytosol of live cells^[3] and for their intracellular delivery by electroporation. Their high brightness enabled unprecedented single-particle tracking in the mice brain and visualization of crossing blood-brain barrier.^[7] Assembling dyes inside small polymeric NPs revealed also a unique cooperative behavior of dyes through ultrafast dye-dye energy migration, which led to the collective switching of >100 dyes in a single particle.^{[4, 6]} This collective behavior of dyes enabled efficient Förster resonance energy transfer (FRET) from ~10000 encapsulated dyes to a single acceptor. This light-harvesting nanoantenna provided >1000-fold signal amplification (antenna effect), allowing first single-molecule detection in ambient light.^[8] Functionalization of these nanoatennas with nucleic acids yielded ultrabright FRET-based nanoprobes for amplified detection of oligonucleotides,^[9] opening possibilities for rapid detection of cancer markers using a RGB camera of a smartphone.^[10] Nanoantennas of 20 nm size enabled efficient FRET to a single acceptor at their surface and detection of RNA/DNA with a single-molecule sensitivity.^[11] The light-harvesting concept was also applied to amplify phosphorescence of porphyrins for ratiometric sensing of oxygen with minimal phototoxicity.^[12] The developed small dye-loaded polymeric NPs open the route to ultrabright tools for sensing and tracking biomolecules in biosensing, bioimaging and diagnostics applications.

This work was supported by ERC Consolidator grant BrightSens 648528.

References
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[2] A. Reisch, A. Runser, Y. Arntz, Y. Mely, A. S. Klymchenko, ACS Nano 2015, 9, 5104.
[3] A. Reisch, D. Heimburger, P. Ernst, A. Runser, P. Didier, D. Dujardin, A. S. Klymchenko, Adv. Funct. Mater. 2018, 28, 1805157.
[4] A. Reisch, P. Didier, L. Richert, S. Oncul, Y. Arntz, Y. Mely, A. S. Klymchenko, Nature Commun. 2014, 5, 4089.
[5] B. Andreiuk, A. Reisch, E. Bernhardt, A. S. Klymchenko, Chem. Asian J. 2019, 14, 836.
[6] A. Reisch, K. Trofymchuk, A. Runser, G. Fleith, M. Rawiso, A. S. Klymchenko, ACS Appl. Mater. Interfaces 2017, 9, 43030.
[7] I. Khalin, D. Heimburger, N. Melnychuk, M. Collot, B. Groschup, F. Hellal, A. Reisch, N. Plesnila, A. S. Klymchenko, ACS Nano 2020, 14, 9755.
[8] K. Trofymchuk, A. Reisch, P. Didier, F. Fras, P. Gilliot, Y. Mely, A. S. Klymchenko, Nature Photonics 2017, 11, 657.
[9] N. Melnychuk, A. S. Klymchenko, J. Am. Chem. Soc. 2018, 140, 10856.
[10] C. Severi, N. Melnychuk, A. S. Klymchenko, Biosens. Bioelectron. 2020, 168.
[11] N. Melnychuk, S. Egloff, A. Runser, A. Reisch, A. S. Klymchenko, Angew. Chem. Int. Ed. 2020, 59, 6811.
[12] P. Ashokkumar, N. Adarsh, A. S. Klymchenko, Small 2020, 16, 2002494.

Nature has evolved in a hierarchical manner to achieve outstanding material properties and complex organismal behaviours. While great progress has been made engineering precise nanostructures through the self-assembly of molecular building blocks, the capacity to organize them beyond the nanoscale and into functional macroscopic structures, remains a challenge. In the fields of tissue engineering and regenerative medicine, it is essential to design materials, structures, and processes with hierarchy as a central principle. This talk will present our laboratory’s efforts to exploit biological organization principles to guide self-assembly of multiple types of building blocks across size scales and enable the design of functional biomaterials. Examples will include the use of supramolecular events found in nature based on multicomponent self-assembly, protein order-disorder synergies, diffusion-reaction processes, and/or organic-inorganic interactions to organize multiple types of biological (e.g. proteins, polysaccharides) and/or synthetic (e.g. peptides, surfactants, graphene oxide) building blocks hierarchically. The resulting materials exhibit properties such as hierarchical organization (1-4), the capacity to grow and heal (1,2), tuneable mechanical properties (1,4), and biomimicry (4,5).

References
1. Wu et al (2020). Nature Communications 11, 1182, 10.1038/s41467-020-14716-z.
2. Inostroza-Brito et al (2015). Nature Chemistry 7(11), 10.1038/nchem.2349.
3. Hedegaard et al (2018). Advanced Functional Materials 28(16), 10.1002/adfm.201703716.
4. Elsharkawy et al (2018). Nature Communications 9(2145), 10.1038/s41467-018-04319-0.
5. Hedegaard et al (2020). Science Advances 6(4), 10.1126/sciadv.abb3298.

Living systems can grow a huge variety of materials with the highest degree of sophistication, and an overall efficiency that remains largely unparalleled by artificial fabrication techniques. Moreover, living materials are adaptive i.e. they exist and perform autonomously under dissipative conditions. These features are made possible by the ability to control complex reactions networks, carefully organized in spatiotemporal sequences.
Developing autonomous chemical systems that could imitate the properties of living matter is a challenge at the meeting point of materials science and systems chemistry. Chemical clocks thus become versatile tools to program in time the autonomous and transient self-assembly of organic as well as inorganic building blocks.
The design of such ad hoc reaction networks is at the core of my current research efforts. I will show how to “clock” molecules, polymers and metal cations into different structures, from nanoparticles to gels, without the need for external control, and demonstrate how this approach paves the way to the development of (almost) living artificial materials.

Modern nanotechnology fabrication relies on two opposite approaches, namely the “top-down” and the “bottom-up”. The former typically employs lithography techniques with which one can obtain nanometer-sized (10-100 nm) structures. This conventional "top-down" approach meets ultimately the physical limits, thus the further progress of the lithographic methods is hindered. The alternative, "bottom-up" strategy, utilizes chemical compounds, which self-assemble into more complex structures. An example of such compounds are block copolymers (BCPs), consisting of at least two different homopolymer blocks joined together with a covalent bond.
Our aim is to explore principles governing each block location (degree of order) and control it, prior to subsequent metal/oxide functionalization of such organic template. A straightforward approach, which we call Solvent Evaporation Annealing (SEA), offers a sensible balance between simplicity and economic cost. Here, the ordering process occurs at the same time while the layer is deposited on the substrate in a time-extended spin-coating process. The key element is an introduction of a low volatile compound in the mixture with BCP along with normally present high volatile solvent. Lower solution viscosity combined with an elongated evaporation time delivers a large grain size (more specifically correlation length), which is on the order of single micrometers.
BCP ordered films are designed to serve as matrices for the templated synthesis of inorganic nanostructures. Conversion methods follow the general idea of the affinity of metal precursor molecules to a specific functional group present in a selected homopolymer block. Thus, the metal precursor renders a pattern marked by one domain. Wet techniques accomplish the idea by a solution-based chemical reaction with a polymer, sometimes acting destructively on the polymer morphology. In our research, we combined Solvent Evaporation Annealing with the addition of metal precursor salt to successfully obtain BCP-templated metal nanostructures. The technique requires only the use of the spin-coating device and a proper selection of cosolvent with dissolved metal precursor salt. We have tested several compounds with metals incorporated, which reproduce the pattern of preferential homopolymer block. We further characterized the morphology of the obtained samples. Our profound investigations about this convenient process may open the facile way for obtaining precisely tuned functional nanostructures with sizes not exceeding single nanometers, which potential area of application ranges from membranes through memory devices to optical coatings.

Large scale block copolymer self-assembly is hindered by relatively low defect formation energy – leading to high defect density, and relatively slow ordering kinetics. There are many processing methods used to overcome these obstacles, all aiming at obtaining highly ordered morphologies in a time- and cost-efficient manner. Among them, the two most straightforward techniques have been extensively explored – thermal annealing and solvent vapor annealing (SVA).
Solvent evaporation annealing (SEA) is a method based on a concept similar to SVA – in both cases, the acceleration of block copolymers self-assembly is obtained by an increase of mobility of polymeric chains in a presence of solvent molecules. However, instead of swelling of dry polymer film, in SEA preferable ordering conditions are achieved by evaporation of the solvent during single-step casting. It is possible due to binary solvent mixtures, in which the dominant solvent is much more volatile than a second one. Unlike in conventional spin-coating, during the casting process, the non-volatile addition remains in a block copolymer film for a significantly longer time. This residual solvent in a polymer wet film prolongs the evaporation process. We monitor the block copolymer grain coarsening – the long-range ordering of polymer domains – by control of multiple parameters, such as residual solvent concentration, temperature, and pressure of the environment.
In this study, we present kinetic data of grain growth in cylindrical block copolymer with a molecular weight range from 58 kg/mol to 275 kg/mol, consisting of polystyrene and poly(vinyl pyridine) blocks, conditioned in different solvents mixtures and varying environmental conditions. The evaporation rate was controlled in both isothermal and non-isothermal manner. We determined a critical concentration of solvent in block copolymer wet film, at which order-disorder transition occurs. Moreover, we conducted a series of experiments in which different pathways of evaporation were scrutinized, including rapid quenches at certain thicknesses and delay of evaporation. The image analysis results were corroborated by large-scale SEM images and GISAXS studies. The obtained results indicate, that there is a power-law scaling between grain coarsening and evaporation rate as well as the time of retention near ODT.
SEA is a convenient method for the fast and cost-effective production of large block copolymer grains. In contrast to many other self-assembly methods, this technique is relatively simple and can be utilized without any complex processing setup.

Nanostructured and hierarchical assemblies are important for demonstrating the ability to understand directed or self-directed forces in defining function for polymers. Knotted and catenated macromolecular architectures in polymers are a departure from typical linear polymers. The lack of chain-ends, the topologically exact order, size, and composition can influence properties and applications such as rheology modifiers, adhesion promoters, and compatibilizers. Herein we demonstrate a supramolecular assembly approach towards these topologically exact polymers and demonstrate their self-assembly properties at interfaces. First, we demonstrate their programmable synthesis—next, their complexation and assembly properties. The goal is to understand structure-composition-property correlation at the macromolecular assembly scale and compare it to other architectures such as stars, dendrimers, and brushes. The ability to self-assemble at the air-water interface is demonstrated with PLA-PCL copolymers and catenanes, and the role of metal complexation is highlighted. Different surface-sensitive analytical spectroscopic and microscopic properties are utilized and reported.

With distinct intermolecular network and dynamics, interfacial water is essential to modulate the surface behaviors, like growth and dissolution, redistribution of surface charge, and dewetting/rewetting surfaces. It plays a crucial role in nano-fluidics, tribology, doping of semiconductors, (geo)-mineralization, and bio-macromolecule and nanoparticle assembly. Hence, characterizing and understanding the structures and dynamics of interfacial water is essential in designing and creating advanced materials.
In the last decade, it has been found that few-layer water confined between solid surfaces in sub-nanoscale can convert into two-dimensional (2D) ice-like structure (i-water). Although its growth dynamics and transition to three-dimensional phases, water droplets, and vapor, in response to humidity, temperature, organic vapor, and hydrophobicity of confining solid surface have been studied, it is unclear if there are other 2D water phases in sub-nanoscale confined space thermodynamically stable, and how it responses to environmental stimuli. The phase diagram of the confined 2D water in sub-nanoscale is not complete.
Recently, using in-situ thermal atomic force microscopy, we have confirmed the exitance of 2D monolayer fluidic water confined by few-layer graphene and muscovite mica. The new phase thickness is less than 0.2 nm, adapting one unique hydrogen-bond network different from bulk water and i-water. It is a thermodynamically stable phase that coexists with i-water. The discovery of this new 2D water phase fills one missing part of the phase diagram of the confined 2D water in sub-nanoscale. It provides another opportunity to understand the physics of fluidics in the nanoscale other than the classical carbon nanotubes and protein-based nanopores. It will also inspire the new theory and scheme in understanding how interfacial water response to confinement and how such modulation can adjust material assembly.

Competing relaxation mechanisms have been extensively modeled for strained and single-crystalline semiconductor nanomembranes (NMs) upon release from their substrate surface. As a result, a variety of 3D structures can be obtained by self-assembly of semiconductor NMs with a high degree of predictive control on their geometry. These structures include wrinkles, helices, twists, and rolled-up tubes. Guided self-assembly of metal NMs into different 3D objects has also been demonstrated. However, the ability to determine the relaxation pathway of a free-hanging metal NM remains elusive. A significant challenge in achieving predictive control on the geometry of metal NMs upon release from their substrate surface relates to a varying stress distribution across the NM thickness for a given set of deposition parameters. Moreover, different stress vs. thickness distributions have been reported for metals with low and high adatom mobilities.
Here, we demonstrate predictive control on the relaxation of metal NMs upon release from their substrate surface. The work encompasses continuum mechanics modeling and synthesis of 3D microstructures via self-assembly of metal NMs.
We investigate NMs comprising Cr and Au, i.e., metals with low and high adatom mobility. We use a force balance model to determine the preferential geometry of a released Cr and Au-based NMs as a function of various parameters. These parameters include the Cr and Au layer thickness, the number of Cr and Au layers and their stacking order within the NM, the substrate surface, and the two metals’ deposition rates. The focus is on metal NMs obtained by evaporation. We also establish how the NMs’ lateral geometry on the substrate surface will affect its self-assembly pathway upon release.
Our theoretical study yields the conditions to obtain rolled-up and inverted rolled-up tubes, helices and twists with an unprecedented degree of control on their diameter and pitch in the microscale range.
We validate our predictions via a comparison with experimentally fabricated 3D structures via guided self-assembly of Cr and Au-based NMs. The NMs are deposited via e-beam evaporation on bulk Si substrates coated with a sacrificial layer. In our work, we use Ge, GeO_x, and SiO₂ sacrificial layers. Upon selective removal of the sacrificial layer, we observe the formation of rolled-up structures by either upward or downward bending of the NM based on the NM composition, sacrificial layer, and thickness of the Cr and Au layers. The fabricated structures include tubes, helices, and twists. The geometry of the fabricated structures is consistent with the prediction of our model.

In conclusion, we have provided the theoretical framework to fundamentally understand and determine competing relaxation pathways for metal NMs that have been released from their substrate surface. Our work is timely and relevant as self-assembled metal NMs are increasingly proposed for various device applications (e.g., integrated inductors and transformers, slow-wave structures, and unit cells of metamaterials).


ACKNOWLEDGEMENT. The work was funded by US AFOSR under award No. FA9550-19-1-0086. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the US Department of Energy (DOE) Office of Science by Los Alamos National Laboratory (Contract 89233218CNA000001) and Sandia National Laboratories (Contract DE-NA-KE,0003525).

As a special class of nanomaterial fluorophores, DNA-templated silver nanoclusters (DNA/AgNCs) have become important in molecular sensing, creating new tools for detection of metabolites, neurotransmitter and metal ions. Despite of their unique capabilities in molecular sensing, the mechanisms that mediate both the formation of DNA/AgNCs and the resulting optical properties are largely unknown. Here we utilized an advanced mass spectrometry, including electron spray ionization (ESI-MS) and activated-electron photodetachment mass spectrometry (aEPD-MS), to probe the fluorescence and structural properties of DNA/AgNCs, including stoichiometries, compositions and binding sites of DNA/AgNCs templated in seven DNA 10-mers. Our mass spectrum data revealed the presence of complexes containing one (monomeric) or two (dimeric) DNA hosts and a variable number of silver atoms. Interestingly, while monomeric species incorporated a low number of silver atoms (Ag₁ - Ag₄), the dimeric complexes contained a higher number of silver atoms (Ag₄ - Ag₁₈). Using polyacrylamide gel electrophoresis (PAGE), we validated that the higher number of silver atoms are associated with dimers responsible for the red fluorescence emission, while the low number of silver atoms are monomers that tend to give green fluorescence emission. The formation of nanocluster cores and the resulting spectroscopic properties vary by the base composition of the DNA template. Given the enhanced abundance of specific dimeric DNA/AgNCs, we hypothesize that certain magic-number of Ag atoms (e.g., Ag₆, Ag₁₀, and Ag₁₁) with dimerization of short DNA may be a clue for having fluorescence with the different emission wavelengths (490 – 680 nm) observed. This study suggests that fluorescence can be strategically controlled by the certain design (e.g., consecutive cytosines and GC contents ratio) of the DNA host to guide the formation of monomeric or dimeric species with magic-number of silver atoms.
References:
1. M.S. Blevins, D. Kim, C.M. Crittenden, S. Hong, H.-C. Yeh, J.T. Petty and J.S. Brodbelt, "Footprints of nanoscale DNA-silver cluster chromophores via activated-electron photodetachment mass spectrometry", ACS Nano 13, 14070-14079, 2019.
2. I.C. Santos, S. Hong, H.-C. Yeh and J.S. Brodbelt, "Electron photodetachment mass spectrometry to study interactions of silver nanoclusters with DNA monomers and dimers", under review.

Epoxy/block copolymer (BCP) blends have shown great promise in a variety of applications. The BCPs can form nanostructures in the resins, which improve the toughness of the thermoset as well as provide a template for nanoparticles (NPs). However, the BCPs can either form the nanostructures through reaction induced microsphase separation (RIMPS) or by self-assembly. For toughness applications, the mechanism is not as critical, but for NP templating, the self-assembly mechanism is preferred in order to help mitigate NP aggregation. In this work, we demonstrated that using an ionic liquid (IL) hardener, rather than a traditional diamine hardener, results in the formation of the nanostructures through self-assembly rather than RIMPS for poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (Pluronic) BCPs. Small angle x-ray scattering (SAXS) was used to develop a ternary phase diagram that shows a range of stable nanostructures including higher ordered cubic, hexagonal and lamellar structures, even in these highly polydisperse BCPs. Additionally, in situ small angle x-ray scattering (SAXS) was used to show that there are significant morphological transitions during epoxy curing. These data show that there are competing changes that are driven by the epoxy cross-linking reactions and the increased thermal mobility of the BCPs in the epoxy. These results demonstrate new methods to drive self-assembly in epoxy/BCP blends, which is critical for their development as multifunctional nanocomposites.

Amphiphilic block copolymers combined with lipid-based amphiphiles are capable of self-assembling into hybrid bilayers with properties of both lipid and polymer that are not always predictable. We aim to understand and predict the properties of polymer and hybrid vesicle membranes to better exploit them for use in drug delivery and modulating surface properties in biosensing devices. One of those key properties is the surface charge of vesicles, which influences how a membrane will interact with other materials and biological tissues, as well as the biological fate of vesicle assemblies in vivo. To study the modulation of surface charge in hybrid lipid/polymer bilayers, we have used DLS and zeta potential analysis to investigate the effects of incorporating charged lipids and polymers into hybrid lipid-polymer vesicles. We have found that polymer amphiphiles containing polyethylene oxide headgroups have a surprisingly strong ability to screen charged lipids within the vesicle membrane, complicating the task of predicting the surface properties of hybrid vesicles. To explain these results and provide a straightforward way of predicting the surface properties of synthetic, multicomponent membranes, we have devised a model that allows us to predict the zeta potential of hybrid vesicles quantitatively. We anticipate that our approach will greatly facilitate modulating zeta potential and other surface properties of biomimetic membrane materials.

The controllable nanoscale self-assembly of biomolecules, such as peptides, on solid surfaces is an important issue in establishing functional bio/solid interfaces for biosensors. Two-dimensional (2D) nanomaterials such as graphene and MoS2 are gaining a wide attention due to its unique electrical properties as a novel platform for biosensing. For this sake, we have established a method to control the self-assembly on these 2D materials by applying electrochemical bias¹ and designing new sequence of peptides². In this work, we studied basics of the assembly process of the self-assembling peptide Y(GA)₄Y: (Y4Y) on 2D materials by employing methanol (MeOH) and other organic solvents as mediators.
Flakes of graphite and MoS₂ were transferred on to silicon wafers by mechanical exfoliation method. A solution of Y4Y peptide (100 nM) dissolved in a mixture of water and methanol (MeOH) at different concentrations ranging from 0% to 50% were placed on both substrate graphite and MoS₂. After 1 hour of the incubation, the solution was removed by blowing with N₂ gas and the sample was dried overnight. Finally, Atomic Force Microscopy (AFM) characterization and analysis were carried out.
AFM analysis showed that. by using aqueous solution as a medium for the self-assembly of Y4Y, more than 85% of self-assembled peptide covered (coverage) the surface of graphite and MoS₂ forming a monolayer in the shape of nanowires with a hexagonal structure. When MeOH was employed as the mediator of Y4Y self-assembly, the coverage decreased drastically for both substrates at distinct threshold concentrations. While the coverage of peptides decreased to ~60% at more than 30% of MeOH concentration on graphite, the peptide coverage resulted in ~50% at more than 20% of MeOH for MoS₂. Higher concentrations of MeOH resulted in no self-assembled peptide for both substrates, thus evidencing the effect of MeOH in controlling the coverage of Y4Y structure over graphite and MoS₂. Additionally, we evaluated the influence of other water-miscible organic solvents (DMSO and acetone) in the self-assembly process of peptide on graphite and MoS₂. These AFM characterizations suggested that the organic-solvent mediated self-assembly process of peptide on 2D materials correlates with the relative polarity of the respective organic solvent. These results unveil promising properties of organic solvents as peptide self-assembly mediator on 2D materials.

(1) T. Seki, C. Page, D. Starkebaum, Y. Hayamizu, M. Sarikaya, Langmuir, 34, 1819 (2018).
(2) P. Li, K. Sakuma, S. Tsuchiya, L. Sun, Y. Hayamizu, ACS Appl. Mater. Interfaces, 11, 20670 (2019).

Recent clinical successes of checkpoint inhibitors have led to a renaissance in the field of cancer immunotherapy. Combinatorial immunotherapy that targets multiple immune pathways offers a more potent strategy to improve patient outcomes. However, combination immunotherapies generally suffer from increased risk of immune-related adverse events that limit their utility. Optimal sequencing, timing, and duration of exposure of immune-modulators that resonate with the natural immune cycle can help rescue systemic toxicity and unleash the full potency of combination immunotherapies. Rational biomaterials- and nanotechnology-based drug delivery strategies that allow precise spatiotemporal control of the in vivo presentation of the immune-modulators can open the door to more effective immunotherapies.

One such strategy is the layer-by-layer (LbL) self-assembly technology which enables the fabrication of a modular drug delivery platform with multiple immune-modulating drugs stacked in a layered structure. The sequence of assembly of the bioactive agents and the choice of intervening non-bioactive “glue” layers provide precise control over the timing and duration of exposure of the assembled immune-modulators. Here, we present LbL-assembled structures on injectable microparticles as a tractable drug delivery system to achieve appropriately-timed delivery of poly(I:C), a TLR3 agonist, and interleukin-2 (IL-2), a pro-inflammatory cytokine. To fabricate the microparticle vaccines, the heparin-binding capability of IL-2 was leveraged and poly(I:C), a negatively-charged synthetic mimic of viral dsRNA, was employed as one of the polyelectrolytes in the LbL assembly. The chosen polycation functions as the “glue” layer to enable sequential assembly of the negatively-charged heparin/IL-2 complexes and poly(I:C), as well as to control their rate of release. Encapsulation efficiencies of 30-50% and 60-90% for poly(I:C) and IL-2, respectively, at a high formulation yield (> 80%). For a milligram of the microparticle core, a single layer of IL-2 and poly(I:C) can hold 3-4 μg and 5-10 μg, respectively. Differential release rates of IL-2 from the LbL- microparticles were achieved by the choice of polycations. While LbL-microparticles built with the hydrolytically-degradable poly(β-amino ester) (PBAE) as the polycation released ~90% IL-2 over three days, less than 15% was released from the formulation with the non- degradable poly(L-lysine) (PLK) over eight days. A 4:1 mixture of PBAE and PLK yielded an intermediate release profile with 45% of loaded IL-2 released over eight days. For LbL-microparticles loaded with both poly(I:C) and IL- 2, the release kinetics were adjusted to achieve faster release of poly(I:C) (~90% over 3 days) required to trigger the innate immune response followed by a slow, sustained presentation of IL-2 over multiple weeks to augment the developing adaptive immunity. The microparticle vaccines were further characterized in subcutaneous murine tumor models to evaluate the time-course effects of the LbL-delivered poly(I:C) and IL-2 on immune activity, toxicity, and therapeutic efficacy.

LbL microparticle vaccines, thus, present a new paradigm to evaluate drug sequencing in combination immunotherapies in higher throughput than currently possible with conventional dosing in pre-clinical in vivo experiments.

Peptide materials have a wide array of functions from tissue engineering, surface coatings, catalysis, and sensing. This class of biopolymer is composed of a sequence of 20 naturally occurring amino acids. As the peptide sequence increases, so does the searchable sequence space (trimer = 20³ or 8,000 peptides and a pentamer = 20⁵ or 3.2 M). Empirically, peptide design is guided by the use of structural propensity tables, hydrophobicity scales, or other desired properties and typically yields <10 peptides per study, barely scraping the surface of the search space. Here, we combine machine learning techniques, such as Monte Carlo tree search and random forest, with coarse-grained molecular dynamics (MD) simulations to efficiently search large spaces of trimer, pentamer and octamer peptide sequences with high self-assembly propensity. Subsequent experiments on identified sequences support our findings, and demonstrate the ability of this approach for peptide design.

We report and investigate a novel approach to self-assembly of complex oxide-based nanomembranes (NMs) in radial geometries, including radially stacked complex oxides and complex oxides/single-crystalline semiconductors superlattices. These structures will offer a tremendous opportunity for discovery-driven science and new functionalities. For example, the proximity of single-crystalline semiconductors and complex oxides will potentially result in superlattices with intriguing magnetic and electronic properties through modulating the oxides' intrinsic spin-lattice coupling and other coupling effects. Moreover, we expect that curvature will significantly affect the electronic band structure of the stack and produce unique electrical and thermal transport features.
Amorphous SrTiO₃/Si/Si_1-xGe_x nanomembranes (NMs) roll up into micron-scale tubes upon release from the growth substrate due to the elastic relaxation of stress from two sources: (i) the epitaxial mismatch of SiGe and Si and (ii) stress resulting from the deposition of the amorphous SrTiO₃. Crucially, the NMs are in a metastable structural configuration after release because the SrTiO₃ layer remains in the amorphous state.
Heating transforms NMs scrolls into swiss roll structures that alternate single-crystalline semiconductors and amorphous complex oxides in a radial geometry. A detailed continuum mechanics study establishes that the relaxation of the hybrid NM during heating involves large irreversible compressive stress arising from structural changes in the oxide. Mechanical modeling also shows that this stress is responsible for NM assembly. X-ray reflectivity, x-ray diffraction, and transmission electron microscopy probe changes in the structure of the SrTiO₃ layer that are consistent with densification of the complex oxide.
Based on our experimental results and continuum mechanics modeling, we predict that a variety of complex oxides-based heterostructures can be obtained via reconfiguration-driven assembly of amorphous oxides, including SrTiO₃/Si and SrTiO₃/LaAlO₃.
ACKNOWLEDGEMENT. This research was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award # DE-SC0020186 (electron microscopy, data analysis, and mechanical modeling) and by the National Science Foundation (NSF) under Award # DMR-1720415 (synthesis of the samples). This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Los Alamos National Laboratory (Contract 89233218CNA000001) and Sandia National Laboratories (Contract DE-NA-KE,0003525). X-ray diffraction was performed at the XRD2 beamline within the Laboratorio Nacional de Luz Sincrotron.

Cellulose nanomaterials (CNM) have emerged in the last decades as a potential candidate for renewable thermally insulating foams and aerogels ^[1]. The intrinsic anisotropy of cellulose chains has been exploited in the design of anisotropic foams with aligned nanoparticles and lower-than-air thermal conductivities in a specific direction ^[2]. It was recently shown ^[3] that the (nano)porosity, particle alignment and tailoring of heterogeneous interfaces can have a significant effect on the heat transfer properties within foams. Here, we will present work on the heat transfer and mechanical properties of ice-templated anisotropic foams based on TEMPO-oxidized cellulose nanofibrils (TCNF) and cellulose nanocrystals (CNC). Anisotropic CNM-based foams with a wide range of densities were prepared by freeze casting aqueous dispersions with different particle concentrations. We will discuss how the radial thermal conductivity (perpendicularly to the freezing direction) of the foams was related to the nanoporosity in the pore walls and the degree of particle alignment. It will also be shown that ice-templating of composite foams, by adding for instance montmorillonite clay nanoplatelets or colloidal silica ^[4], could mechanically strengthen the foams while specific co-assemblies could favor certain heat dissipation mechanisms and therefore preserve or even improve the thermal insulating performance.

References

[1] N. Lavoine, L. Bergström, J. Mater. Chem. A 2017, 5, 16105.
[2] B. Wicklein, A. Kocjan, G. Salazar-Alvarez, F. Carosio, G. Camino, M. Antonietti, L. Bergström, Nat. Nanotechnol. 2015, 10, 277.
[3] V. Apostolopoulou-Kalkavoura, P. Munier, L. Bergström, Adv. Mater. 2020, 2001839, 1.
[4] P. Munier, V. Apostolopoulou-Kalkavoura, M. Persson, L. Bergström, Cellulose 2019, 1.

Nanoparticle assembly can enable broad applications in electronics, optics, optoelectronics, resonators, and thermal dissipations or conductions. Current methods to tailor nanoparticle structures include electrical field, magnetism, mechanical stretching, surface functionalization, and template directing. Most subtracts for template-based nanoparticle assembly have crimpled surfaces from elastomer compression, transfer imprinting, and other methods with similar slow-manufacturing. Our study has demonstrated the use of different 3D printing, including stereolithography (SLA) and continuous liquid interface processing (CLIP), in making microscale surface patterns for nanoparticle assembly. Via the combination of 3D printing and layer-by-layer assembly (LbL), we demonstrated the capability of aligning nanoparticles between surface grooves. The density of the aligned particles will transport electrons or phonons with different efficiencies. As a result, these rapidly prototyped devices showed varied conductivity and sensitivity. We demonstrated the manufacturability and scalability of our manufacturing with different nanoparticles. The inclusion of these nanoparticles with different concentrations showed high sensitivity and selectivity to different gas analytes, making them ideal platforms for detecting toxic gases or monitoring human health.

Studies of block copolymer (BCP) materials and their phase separation in bulk and thin-film forms have exploded over the last decades, due to the wide range of accessible morphologies (e.g. spheres, cylinders, gyroid, and lamellae) and sizes (5-200 nm) of features. The phase separation of a BCP is governed by three factors which include the relative volume fraction (f) of the blocks A and B (f_A = 1 – f_B), the degree of polymerization (N), and the Flory-Huggins interaction parameter (χ). The basic BCP self-assembly principles have enabled the BCP community to control the morphology as well as to tune the domain size and have driven the community to target the smallest size possible by synthesizing BCPs with high interaction parameter. Accessing sub-5 nm feature size is no longer a challenge utilizing BCP self-assembly. However, transferring the self-assembled BCP features to a substrate over a large area with high fidelity presents additional challenges, especially at the 10 nm length scale. In this work, the highly polar, functional and hydrophilic poly(3-hydroxystyrene) (P3HS) is incorporated with the acid sensitive poly(dimethylsiloxane) (PDMS). A tetrahydroxydropyranyloxy (THP) protecting group which requires mild deprotection condition is introduced to the system and hence PDMS block remains intact after deprotection. We explore both P3HS/PDMS-based diblocks and triblocks synthesized by sequential living anionic polymerization and atom transfer radical polymerization, respectively. P3HS-b-PDMS shows well-defined lamellae or hexagonally packed cylinders with characteristic dimensions ranging from 7.4 to 17.7 nm. Mean-field theory analysis of the temperature-dependent correlation-hole scattering derived from a disordered symmetric P3HS-b-PDMS gives χ_(T) = 33.491/T + 0.3126, which is more than 4-fold increase over PS-b-PDMS. Triblocks P3HS-b-PDMS-b-P3HS also show well-ordered lamellae and cylinder structures in bulk with the successful access to sub-5 nm feature size. Additionally, the unique architecture of ABA triblock allows the thin film of P3HS-b-PDMS-b-P3HS to be aligned vertically to the substrate, making this material a promising candidate for pattern transfer. Etching study indicates that the etch contrast between P3HS and PDMS is 15:1 under oxygen plasma treatment. Due to the functionality from the hydroxy group, inorganic precursors such as trimethylaluminium can selectively penetrate into P3HS domain which can be further converted into alumina mask for pattern transfer. These new BCPs not only exhibit high interaction parameter to achieve sub-10 nm feature size, but also present high etch contrast and versatile etch selectivity to facilitate the pattern transfer.

Self-assembly is a powerful way to organize small molecules with tunable molecular chemistries into nanostructures with high surface areas. However, in order to exploit molecular self-assembly, the molecules must be amphiphilic and must fulfill particular packing parameter guidelines. These constraints have limited the use of small molecule self-assembly to a narrow range of molecular species with specific chemical attributes. Here, we introduce a new approach to supramolecular nanoribbons composed of untraditional hydrophobic small molecules. We pre-program into the nanostructure thermal stability in hydrophobic domain, and we use thermal decomposition to selectively remove the hydrophilic labile groups. The selective decomposition of labile groups with maintained nanoribbon morphology was confirmed by the combination of thermogravimetric analysis with mass spectrometry, ¹H NMR, and infrared spectroscopy. This molecular design strategy represents a new pathway to non-amphiphilic small molecule nanostructures through domain-specific selective decomposition, and broadens the potential utility of this materials class for new targets, including superhydrophobic coatings and self-assembled molecular electronics.

Melanin, a natural pigment known for imparting color to human skin/hair, is mimicked in synthetic materials for use in a variety of applications with the desired optical, photonic, thermal, and electrical property. In the past decade, polydopamine has served as one such synthetic form dominating the fundamental and applied research on melanin-based materials. While past experimental studies have focused on the synthesis and characterization of these melanin synthetic mimics, much less is known about the preferential interactions of these materials with other polymers, biocompatible and/or bio-derived. In this work, we use atomistic molecular dynamics (MD) simulation to simulate synthetic melanin nanoparticles, self-assembled using oligomers (e.g., 2-mer, 4-mer, and 8-mer) of polydopamine in an explicit solvent with and without added polymers, poly (ethylene glycol), and chitin. Using these simulations, we understand the nature of the polydopamine nanoparticle surface and its interactions with these polymers. We quantify the hydrophobic vs. hydrophilic character of the surfaces of the different assembled polydopamine oligomers, behavior of water molecules near the surface in the presence and absence of biopolymers. The impact of the polydopamine nanoparticle surface on the polymer is quantified via pair-wise correlation functions, polymer-particle hydrogen bonds, chain conformations, and interaction with water in the presence/absence of the polydopamine particle.

From extrusion, melt-blown Isotactic polypropylene (iPP) submicron fibers were produced to be used in air purification. Scanning Electron Microscopy images revealed the lower the iPP molecular weight (MW), the lower the resulting melt-blown fiber diameter. For iPP fibers with MW~50 kg/mol, the average diameter was ~0.7 µm. The base weight in the melt-blown mats was adjusted by tuning the collector speed. Filtration properties, namely air resistance (AR) and filtration efficiency (FE%), were measured for the melt-blown iPP mats with different base weight, 5-75 gsm. Filtration efficiency increased exponentially as air resistance increased almost linearly with base weight. However, the filtration quality factor (Qf=-ln(1-FE/100)/AR) was the highest, ~0.04 Pa^-1, at 50 gsm. The effect of discharging, using saturated isopropyl alcohol (IPA) vapor, on filtration quality factor was also studied. The mats maintained ~50% of their filtration quality factor, reflecting the existence of residual electrostatic charges from the melt-blown process and their significant effect on filtration.
Charge retention is crucial in air filter media, in which the nonwoven fibers are electrically charged. Nano-roughness is known to improve hydrophobicity at the solid-liquid interphase. In this work, nano-roughness is introduced to melt-blown iPP fibers via the formation of shish-kebab crystallites.
The shish- kebab formation seems to occur only in the presence of high MW iPP chains. Hence, using microscopy and thermal analysis, crystalline structure in melt-blown iPP fibers with MW~50 kg/mol was studied; at the presence of different amounts (0.0-12.8 wt.%) of high MW~500 kg/mol iPP, blended via melt extrusion. In addition, electrical charge retention in the resulting nonwoven media was investigated through discharging, using saturated IPA vapor. Not only from microscopy and thermal analysis was it evident that the shish-kebab structure was most prevailing for the iPP fibers with 3.0 wt.% high MW component, but also charge retention was the highest for these fibers. Based on the increasing trend in fiber diameter and melt viscosity among fibers with 3.0-12.8 wt.% high MW component, the smaller presence of shish-kebab in the crystalline structure of theses fibers is attributed to lower elongation in the melt-spinning process for these fibers. The shish-kebab structure adds nano-roughness to the surface of the melt-blown iPP fibers, causing the formation of IPA droplets to become more difficult. This seems to contribute to the resulting fibers' resistance to IPA-induced discharging.

In the last decades, growing concerns in global warming and environmental issues have inspired developments of diverse green and sustainable energy technologies. In particular, proton exchange membrane fuel cells (PEMFCs), which produce electrical energy from hydrogen fuel, have gained significant interests as one of the leading candidates to replace conventional internal combustion engines that rely on hydrocarbon fuels. Despite their low greenhouse gas emissions, PEMFCs have been limited to niche applications due to the high cost and scarcity of platinum, which is an essential electrocatalyst material in the energy conversion system. Consequently, most commercially available PEMFCs have adopted composite catalysts in forms of platinum nanoparticles randomly dispersed on zero- or one-dimensional carbon support materials to increase its catalytic efficiency and minimize the noble metal load. However, such platinum/carbon (Pt/C) electrocatalysts have yet to meet the cost, catalytic activity, and durability requirements to be commercially viable and demand further improvements in the electrocatalytic performance via morphological and compositional control.
Here, we present a fabrication method based on block copolymer self-assembly for highly controlled carbon-platinum composite electrocatalysts with superior catalytic performance. Self-assembled diblock copolymers were used as structure-directing frameworks, selectively incorporated with platinum precursor ions, and pyrolized to prepare carbon-metal composite nanostructures with well-defined, three-dimensional morphologies. The calcination process produced evenly distributed, size-controlled platinum nanoparticles embedded in the carbon matrices, which increased the carbon-metal interactions and enhanced the durability of the catalytic materials. We also discuss a novel self-assembly technique to develop hollow channels throughout the carbon support structures using the chemical differences between the two polymer blocks. The three-dimensional morphologies and hollow channels provided pathways for superior mass transport within the nanostructures and enhanced the catalytic activity of the noble metal nanoparticles. Electrochemical evaluations revealed that the fabricated composite nanostructures exhibited greater electrochemical surface area and durability compared to those of commercially available Pt/C catalysts, demonstrating the significant enhancements in the catalytic properties made via morphological controls.
In addition, the fabrication process can be utilized to develop composite nanostructures with various noble metals other than platinum. We demonstrated three-dimensional composite nanostructures prepared with a number of noble metals nanoparticles, including ruthenium, rhodium, osmium, and iridium nanoparticles, embedded in carbon matrices. The block copolymer self-assembly technique was also employed here for flexible control of the nanostructures, including formation of the hollow channels. The versatility of the process can be utilized to fabricate composite nanostructures of carbon and noble metals arranged in diverse morphologies and compositions, optimized for respective applications.

Hydrogels are emerging biomaterials with desirable physicochemical characteristics. Doping of metal ions such as Ca²⁺, Mg²⁺, and Fe²⁺ provides the hydrogels with unique attributes, including bioactivity, conductivity, and tunability. Traditionally, this doping is achieved by the interaction between metal ions and corresponding ligands or the direct incorporation of as-prepared metal-based nanoparticles (NPs). However, these approaches rely on a complex and laborious preparation and are typically restricted to few selected ion species. Herein, by mixing aqueous solutions of ligands (bisphosphonates, BPs), polymer grafted with ligands, and metal ions, a series of self-assembled metallic-ion nanocomposite hydrogels that are stabilized by the in situ formed ligand-metal ion (BP–M) NPs are prepared. Owing to the universal coordination between BPs and multivalent metal ions, the strategy is highly versatile and can be generalized for a wide array of metal ions. Such hydrogels exhibit a wide spectrum of mechanical properties and remarkable dynamic properties, such as excellent injectability, rapid stress relaxation, efficient ion diffusion, and triggered disassembly for harvesting encapsulated cells. Meanwhile, the hydrogels can be conveniently coated or patterned onto the surface of metals via electrophoresis. This work presents a universal strategy to prepare designer nanocomposite materials with highly tunable and dynamic behaviors. Moreover, we demonstrated that the nanocomposite hydrogels doped with lanthanide ions exhibited a highly tunable fluorescent spectrum. We next applied the developed hydrogels to treat peripheral nerve injuries, which are of great clinical significance. We demonstrated that the nanocomposite hydrogels containing magnesium and bisphosphonates promoted peripheral nerve regeneration and achieved partial functional recovery in s sciatic nerve injury rat model.

Controlled synthesis of one-dimensional nanostructures such as nanowires are most fascinating for wide range applications due to their superior performances based on quantum confinement effects. Here, we demonstrate a novel facile and greener synthesis method to fabricate high aspect ratio of one-dimensional CuO nanowires from directed self-assembly of Cu(OH)₂ nanocrystals guided by the oriented attachment mechanism via post-annealing. This surfactant free, one-pot sol-gel route at low temperature allows us to make higher aspect ratio of CuO nanowires with controlled-dimensions over a large area. The respective Raman, XRD and XPS spectroscopies confirm the chemical composition of CuO nanowires and their purity. The synthesized CuO nanowires has average diameter of 26.5±2.4 nm and aspect ratio of 280.9±18.0. Further, the analysis of electrochemical properties of synthesized CuO nanowires have shown the suitability for potential electrochemical applications of capacitors and energy storage devices.

Self-assembly can organize structures beyond the synthesis nanoscale and bridge to macroscale manufacturing, thus providing many device fabrications opportunities. For composite devices, the mixing of nanoparticles in polymers involves dispersion quality, interfacial interactions, and nanoparticle alignment. Among these parameters, the nanoparticle alignment is the most challenging. Our study has shown an efficient way to self-assemble nanoparticles based on surface topologies, roughness, and wetting conditions. In this research, we used photopolymers for the first layer deposition and surface topology control. Following the deposition of nanoparticles complies with this first layer and form cluster-based assembly with different densities. Our manipulation of the nanoparticle density via the secondary-bonding can tune the layered structure's mechanical and electrical properties, thus making them multifunctional devices. The same manufacturing is also applicable in general nanoparticles based on our observation of feasibility using 1D nanofibers and 2D nanoplatelets. The fabricated devices showed enormous potential in microelectronics, sensors, actuators, and smart materials in robotics.

Controlled evaporative self-assembly of semiconducting polymers has mostly been limited to time-consuming solvent evaporation or non-continuous blade-casting techniques. In this study, we report a novel high-throughput continuous printing of poly (3-hexylthiophene 2,5-diyl) (P3HT) by a custom-made oscillatory roller. The roller oscillation generates a cycle of meniscus stick and slip motion per single rotation of the roller that induces a rapid self-assembly of P3HT lines. The printed P3HT lines demonstrate hierarchical structures: nanometer scale thickness, micron scale width, sub-millimeter pattern intervals, and millimeter to centimeter scale length with highly defined boundaries. Remarkably, the line width and the interval of P3HT patterns can be independently controlled by varying polymer concentrations, the rotation rates of the roller, and the stage speed. Furthermore, grazing incidence wide angle X-ray scattering (GIWAXS) revealed that the roller-blading technique dramatically enhances crystallinity of P3HT by shear-induced crystallization. This high-throughput printing process for hierarchical assembly will open new opportunities for printed electronics with wide ranges of engineering capability.

The behavior of colloidal particles has been widely studied with interests in their dynamics and self-assembly. Specifically, since the phase behavior and lattice structures of colloids are similar to those of atoms, the main focus is on how to treat colloids as model atoms. In previous studies, colloids have been primarily considered as hard spheres on which only the infinite repulsion at contact distance is acting. This is to reflect a repulsion between atoms due to the overlap of electron clouds when they are getting close. Such hard-sphere systems have also been realized by matching refractive indices. The real atomic interactions, however, are different from that due to van der Waals (vdW) attraction. They are represented by well-known models such as Lennard-Jones, Mie, and Morse potential. Therefore, a colloidal system that takes attractive interactions into account should be developed for the modeling. Here, in that sense, the phase behavior of colloidal particles with attractive potentials is studied. Systems are designed to have both repulsive and attractive force among particles and analyzed using both DLVO theory and a non-DLVO interaction. To observe crystals with an optical microscope and UV-Vis spectrometer, dielectric colloids are chosen properly so that crystal lattices diffract a selected wavelength in the visible range resulting in structural colors. In experiments, polystyrene nanoparticles (PS NPs) synthesized via emulsion polymerization are used as building blocks. Then, PS NPs, sodium chloride, and poly(Acrylamide-co-acrylic acid) (p(Am-co-AAc)) are mixed with different compositions in de-ionized water. The suspensions are confined in glass cells immediately and observed continuously until reaching an equilibrium state. There are three interactions among PS NPs. VdW attraction arises from the different dielectric constants between PS and water. Electric double-layer repulsion is derived by sulfate groups on the surface of PS NPs, which is reduced by charge screening due to a salt, sodium chloride. A depletion attractive force is given and modulated by depletants, p(Am-co-AAc). Within two days, colloidal systems have been clearly distinguished into 4 phases depending on the composition; each phase is labeled as “fluid”, “crystal/fluid”, “crystal/glass/fluid”, and “glass/fluid“ phase based on whether crystals and aggregates are dominantly formed. At a low concentration of depletant and salt, none of the crystal or aggregate are observed at equilibrium, while only the aggregates are formed at high concentrations. In between, crystals with distinctive structural colors are detected. However, not all of the samples reach the equilibrium states in this short term. It was figured out that after a month, crystals are formed in the samples of which the compositions are at the boundary between the fluid and crystal/fluid phases, and their growth stops after 3 months. Interestingly, these crystals are dendritic-like and much larger over a few mm, while crystals formed in other conditions are polygon-shaped and smaller up to a few hundreds of μm. The interactions are then analyzed with pair-potentials derived from DLVO theory, Lifshitz’s continuum theory, and Asakura-Oosawa’s model. The osmotic contribution of depletants is adjusted theoretically because of its size-dependency. A total pair-potential is calculated by summing up three interaction potentials. From the developed potential curves, which are analogous to the atomic potentials, the information about equilibrium points as well as collision kinetics is obtained. By matching experimental results with pair-potentials, the energetic and kinetic range for the crystallization of spherical colloids have been demonstrated. The validity of analysis is verified using other types and sizes of colloids. In conclusion, the developed colloidal systems with attractive force will be a lot more reasonable to analyze the crystallization in terms of modeling the real atoms.