Binary hairy nanoparticles: Recent progress in theory and simulations

Hedgehog, Chamomile and Multipetal Polymeric Structures on the Nanoparticle Surface: Theoretical Insights

An analytical theory describing the variety of different morphological structures that spontaneously self-assemble in layers of amphiphilic homopolymers tightly grafted to spherical nanoparticle is proposed. For this purpose, the following structures were identified and outlined: hedgehogs, in which macromolecules are combined into cylindrical aggregates; chamomile, when cylindrical aggregates are connected by their ends into loops; multipetal structure with macromolecules self-assembling into thin lamellae; and unstructured, swollen and uniformly compacted shells. The results are presented in the form of state diagrams and serve as a basis for the directional design of the surface pattern by varying system parameters (particle radius, grafting density and degree of polymerization) and solvent properties (quality and selectivity).

Understanding Interfacial Nanoparticle Organization through Simulation and Theory: A Review

Understanding the behaviors of nanoparticles at interfaces is crucial not only for the design of novel nanostructured materials with superior properties but also for a better understanding of many biological systems where nanoscale objects such as drug molecules, viruses, and proteins can interact with various interfaces. Theoretical studies and tailored computer simulations offer unique approaches to investigating the evolution and formation of structures as well as to determining structure-property relationships regarding the interfacial nanostructures. In this feature article, we summarize our efforts to exploit computational approaches as well as theoretical modeling in understanding the organization of nanoscale objects at the interfaces of various systems. First, we present the latest research advances and state-of-the-art computational techniques for the simulation of nanoparticles at interfaces. Then we introduce the applications of multiscale modeling and simulation methods as well as theoretical analysis to explore the basic science and the fundamental principles in the interfacial nanoparticle organization, covering the interfaces of polymer, nanoscience, biomacromolecules, and biomembranes. Finally, we discuss future directions to signify the framework in tailoring the interfacial organization of nanoparticles based on the computational design. This feature article could promote further efforts toward fundamental research and the wide applications of theoretical approaches in designing interfacial assemblies for new types of functional nanomaterials and beyond.

How Does the Number of Arms Affect the Properties of Mikto-Arm Stars in a Selective Oligomeric Matrix? Insights from Atomistic Simulations

We present a simulation study of amphiphilic mikto-arm star copolymers in a selective polymer host. By means of atomistic molecular dynamics simulations, we examine the structural and dynamical properties of mikto-arm stars with varying number, n, of poly(ethylene oxide) (PEO) and polystyrene (PS) arms, (PEO) n (PS) n in a 33% wt blend with an oligomeric PEO host (o-PEO). As the number of arms increases, the stars resemble more spherical particles with less separated PEO and PS intramolecular domains. As a result of their internal morphology and associated geometrical constraints, the mikto-arm stars self-assemble either into cylindrical-like objects or a percolated network with increasing n, within the o-PEO matrix. The segmental dynamics is mostly governed by the star architecture and the heterogeneous local environment, formed by the intra- and intermolecular nanosegregation. We discuss the role of each factor and compare the results with previously published studies on mikto-arm stars.

Polymer-guided assembly of inorganic nanoparticles

The self-assembly of inorganic nanoparticles is of great importance in realizing their enormous potentials for broad applications due to the advanced collective properties of nanoparticle ensembles. Various molecular ligands (e.g., small molecules, DNAs, proteins, and polymers) have been used to assist the organization of inorganic nanoparticles into functional structures at different hierarchical levels. Among others, polymers are particularly attractive for use in nanoparticle assembly, because of the complex architectures and rich functionalities of assembled structures enabled by polymers. Polymer-guided assembly of nanoparticles has emerged as a powerful route to fabricate functional materials with desired mechanical, optical, electronic or magnetic properties for a broad range of applications such as sensing, nanomedicine, catalysis, energy storage/conversion, data storage, electronics and photonics. In this review article, we summarize recent advances in the polymer-guided self-assembly of inorganic nanoparticles in both bulk thin films and solution, with an emphasis on the role of polymers in the assembly process and functions of resulting nanostructures. Precise control over the location/arrangement, interparticle interaction, and packing of inorganic nanoparticles at various scales are highlighted.

Nanostructuring Single-Molecule Polymeric Nanoparticles via Macromolecular Architecture

Heterogeneous polymer-based nanoparticles comprise a very promising family of materials for a broad range of applications. Here, we present a detailed study of structural heterogeneities in nanostructured single-molecule nanoparticles in various environments by means of atomistic molecular dynamics simulations. The nanoparticles consist of mikto-arm star copolymers with two types of chemically incompatible arms, namely poly(ethylene oxide) (PEO) and polystyrene (PS), (PS) _n,(PEO) _n, where n is the number of arms. The immiscibility between the two components gives rise to intramolecularly nanostructured particles. The nanostructured objects resemble either "Janus-like" or "patchy-like" particles, depending on the number or the length of the arms (or both) as well as the interaction with the surrounding medium. The degree of intramolecular heterogeneity increases with increasing number of arms and with decreasing affinity of star components to the polymer host. We provide a detailed analysis of the internal structure of the star-shaped particles, focusing on the intramolecular packing and the spatial arrangement of the arms. The results of our study can be used to design heterogeneous, internally nanostructured particles with two phases of distinct static properties for challenging specific applications of next-generation materials.

Hierarchical Superstructures Assembled by Binary Hairy Nanoparticles

Hierarchical superstructures assembled by binary mixed homopolymer-grafted nanoparticles are investigated by using a self-consistent field theory (SCFT). Our results demonstrate that grafting mixed homopolymer brushes provides an effective way to program the spatial lattice arrangement of the nanoparticles. For the polymer-grafted nanoparticles with specific interaction parameter and total grafting density, the unusual non-close-packed simple cubic (SC) crystal lattice is obtained at small spherical core/polymer size ratios (R/([Formula: see text]) < 1). As the size ratio increases to [Formula: see text] > 1, the nanoparticle arrangement transforms into a body-centered cubic (BCC) crystal lattice. Meanwhile, some unconventional microphases are formed in the polymer matrix, such as the tetragonal cylinder and simple cubic sphere phases. Furthermore, the two-dimensional (2D) model calculations reveal that the binary hairy nanoparticles prefer to arrange into the lattice in a way they can maintain the free energy-minimizing morphology as an isolated particle. Our findings suggest a possible strategy to design hierarchical nanomaterials composed of unique inorganic/organic hybrid superstructures.

In Situ Characterization of Binary Mixed Polymer Brush-Grafted Silica Nanoparticles in Aqueous and Organic Solvents by Cryo-Electron Tomography

We present an in situ cryo-electron microscopy (cryoEM) study of mixed poly(acrylic acid) (PAA)/polystyrene (PS) brush-grafted 67 nm silica nanoparticles in organic and aqueous solvents. These organic-inorganic nanoparticles are predicted to be environmentally responsive and adopt distinct brush layer morphologies in different solvent environments. Although the self-assembled morphology of mixed PAA/PS brush-grafted particles has been studied previously in a dried state, no direct visualization of microphase separation was achieved in the solvent environment. CryoEM allows the sample to be imaged in situ, that is, in a frozen solvated state, at the resolution of a transmission electron microscope. Cryo-electron tomograms (cryoET) were generated for mixed PAA/PS brush-grafted nanoparticles in both N,N-dimethylformamide (DMF, a nonselective good solvent) and water (a selective solvent for PAA). Different nanostructures for the mixed brushes were observed in these two solvents. Overall, the brush layer is more compact in water, with a thickness of 18 nm, as compared with an extended layer of 27 nm in DMF. In DMF, mixed PAA/PS brushes are observed to form laterally separated microdomains with a ripple wavelength of 13.8 nm. Because of its lower grafting density than that of PAA, PS domains form more or less cylindrical or truncated cone-shaped domains in the PAA matrix. In water, PAA chains are found to form a more complete shell around the nanoparticle to maximize their interaction with water, whereas PS chains collapse into the core of surface-tethered micelles near the silica core. The cryoET results presented here confirm the predicted environmentally responsive nature of PAA/PS mixed brush-grafted nanoparticles. This experimental approach may be useful for the design of future mixed brush-grafted nanoparticles for nano- and biotechnology applications.

Environmentally responsive self-assembly of mixed poly(tert-butyl acrylate)-polystyrene brush-grafted silica nanoparticles in selective polymer matrices

Environmentally responsive self-assembly of nearly symmetric mixed poly(tert-butyl acrylate) (PtBA, 22.2 kDa)/polystyrene (PS, 23.4 kDa) brushes grafted onto 67 nm silica nanoparticles in selective homopolymer matrices [PtBA for the grafted PtBA chains and poly(cyclohexyl methacrylate) (PCHMA) for the grafted PS chains] was investigated using both conventional transmission electron microscopy (TEM) and electron tomography (i.e., 3D TEM). A variety of self-assembled phase morphologies were observed for the mixed brushes in selective polymer matrices with different molecular weights, and these can be explained by entropy-driven wet- and dry-brush theories. In a low molecular weight selective matrix, the wet-brush regime was formed with the miscible chains stretching out and the immiscible chains collapsing into isolated domains. In contrast, when the molecular weight of the selective matrix was higher than that of the compatible grafted polymer chains, the dry-brush regime was formed with the mixed brushes exhibiting the unperturbed morphology. In addition to the molecular weight, the size of nanoparticles (or the substrate curvature) was also observed to play an important role. For small particles (core size less than 50 nm), the wet brush-like morphology with a surface-tethered micellar structure was observed. Finally, the wet- and dry-brush regimes also significantly affected the dispersion of mixed brush particles in selective polymer matrices.