Ordered nanostructures self-assembled from block copolymer tethered nanoparticles

Solution Self-Assembly of Amphiphilic Tadpole-like Giant Molecules Constructed by Monotethering Diblock Copolymer Chain onto a Nanoparticle

The self-assembly behavior of a tadpole-like giant molecule (TGM) constructed from a hydrophobic nanoparticle (NP) monotethered by a single amphiphilic AB diblock copolymer chain was investigated by combining self-consistent field theory and density functional theory in solution. The effects of the hydrophobicities of the B blocks and NPs (i.e., solvent properties) on the self-assembly behavior of the TGMs were investigated in the cases of weak and strong intramolecular interactions (i.e., incompatibilities) between the components of giant molecules, respectively. Besides conventional ordered aggregates (such as spheres, rings, and vesicles) with hydrophobic B-cores covered by NP shells, several aggregates with novel hierarchical structures, including vesicles with NP-inserted hydrophobic walls, bead-string-like micelles, and long cylindrical micelles with NP bumps, were obtained by tuning the solvent properties under different intramolecular interactions. Noteworthy that the simulation results show that the arrangement of the NP bumps on the long cylindrical micelles may have a certain degree of helicity, which means that these micelles may have some unique electromagnetic features such as circular dichroism. Phase diagrams as a function of the hydrophobicities of the B blocks and NPs were constructed to show the formation conditions of these novel structures. These findings can not only offer new insights into understanding of the self-assembly behavior of the TGM in solution but also provide useful guidance for simple and efficient regulation of the morphology, as well as the NP distribution and arrangement of the ordered aggregates in experiments.

Patterning of Polymer-Functionalized Nanoparticles with Varied Surface Mobilities of Polymers

The polymers can be either dynamically tethered to or permanently grafted to the nanoparticle to produce polymer-functionalized nanoparticles. The surface mobility of polymer ligands with one end anchored to the nanoparticle can affect the surface pattern, but the effect remains unclear. Here, we addressed the influence of lateral polymer mobility on surface patterns by performing self-consistent field theory calculations on a modeled polymer-functionalized nanoparticle consisting of immobile and mobile brushes. The results show that except for the radius of nanoparticles and grafting density, the fraction of mobile brushes substantially influences the surface patterning of polymer-functionalized nanoparticles, including striped patterns and patchy patterns with various patches. The number of patches on a nanoparticle increases as the fraction of mobile brushes decreases, favored by the entropy of immobile brushes. Critically, we found that broken symmetry usually occurs in patchy nanoparticles, associated with the balance of enthalpic and entropic effects. The present work provides a fundamental understanding of the dependence of surface patterning on lateral polymer mobility. The work could also guide the preparation of diversified nanopatterns, especially for the asymmetric patchy nanoparticles, enabling the fundamental investigation of the interaction between polymer-functionalized nanoparticles.

Self-assembled morphologies of polyelectrolyte-grafted nanoparticles directed by oppositely charged polymer matrices

Self-assembled structure of polymer grafted nanoparticles is an interesting and growing subject in the field of hybrid electronics and high energy density materials. In light of this, the self-assembled morphologies of polyelectrolyte (PE) sparsely grafted nanoparticles tuned by oppositely charged matrix chains are studied using molecular dynamics simulations. Our focus is to elucidate the effect of matrix chain polymerization on modulating the stretching properties of tethered PE layers, on the self-assembled structuring of nanoparticles. Through varying the matrix chain length and stiffness as well as electrostatic interaction strength, rich phase behaviors of PE coated nanoparticles are predicted, including spherical micelle-like structures being preferred with short matrix chains and percolating network morphologies favored with long matrix chains, which is more pronounced with an enhanced matrix chain rigidness. To pinpoint the mechanisms of self-assembled structure formation, the thickness of grafted layers, the gyration radius of tethered chains, and pair correlation functions between nanoparticles are analyzed carefully. Additionally, electrostatic correlations, manifested as the bridging via matrix chains, are examined by identifying three states of matrix PE chains. Our simulation results may be useful for designing smart polymer nanocomposites based on PE coated nanoparticles.

Self-assembled structure of polymer grafted nanoparticles is an interesting and growing subject in the field of hybrid electronics and high energy density materials.

Hierarchically Chiral Nanostructures Self-Assembled from Nanoparticle Tethered Block Copolymers

Chiral nanostructures of nanoparticle assemblies have attracted tremendous interest for their fascinating functional properties. Herein, through theoretical simulations, we show that nanoparticle tethered block copolymers can self-assemble into hierarchically chiral nanostructures. Two-fold helices are formed in the hierarchically chiral nanostructures: the diblock copolymers form helical supercylinders while the nanoparticles arrange into chiral assemblies wrapped around the helical supercylinders. The hierarchically chiral nanostructures can be formed in a large parameter window. Circular dichroism calculations demonstrate that the coexistence of polymeric helices and chiral nanoparticle assemblies improves the chiroptical activity. These findings can provide guidelines for designing hierarchically ordered chiral nanostructures with advanced functional properties. This article is protected by copyright. All rights reserved.

Fabrication of 2D Block Copolymer Brushes via a Polymer-Single-Crystal-Assisted-Grafting-to Method

Block copolymer brushes are of great interest due to their rich phase behavior and value-added properties compared to homopolymer brushes. Traditional synthesis involves grafting-to and grafting-from methods. In this work, a recently developed "polymer-single-crystal-assisted-grafting-to" method is applied for the preparation of block copolymer brushes on flat glass surfaces. Triblock copolymer poly(ethylene oxide)-b-poly(l-lactide)-b-poly(3-(triethoxysilyl)propyl methacrylate) (PEO-b-PLLA-b-PTESPMA) is synthesized with PLLA as the brush morphology-directing component and PTESPMA as the anchoring block. PEO-b-PLLA block copolymer brushes are obtained by chemical grafting of the triblock copolymer single crystals onto a glass surface. The tethering point and overall brush pattern are determined by the single crystal morphology. The grafting density is calculated to be ≈0.36 nm^-2 from the atomic force microscopy results and is consistent with the theoretic calculation based on the PLLA crystalline lattice. This work provides a new strategy to synthesize well-defined block copolymer brushes.

Polymers on nanoparticles: structure & dynamics

Grafting polymers to nanoparticle surfaces influences properties from the conformation of the polymer chains to the dispersion and assembly of nanoparticles within a polymeric material. Recently, a small body of work has begun to address the question of how grafting polymers to a nanoparticle surface impacts chain dynamics, and the resulting physical properties of a material. This Review discusses recent work that characterizes the structure and dynamics of polymers that are grafted to nanoparticles and opportunities for future research. Starting from the case of a single polymer chain attached to a nanoparticle core, this Review follows the structure of the chains as grafting density increases, and how this structure slows relaxation of polymer chains and affects macroscopic material properties.

Effect of Chain Architecture on Phase Behavior of Giant Surfactant Constructed from Nanoparticle Monotethered by Single Diblock Copolymer Chain

The phase behaviors of the giant surfactant constructed from a nanoparticle (NP) monotethered by a single AB diblock copolymer chain were investigated by combining self-consistent field theory and density functional theory. Three types of giant surfactants with different chain architectures were constructed via changing the location of NP on the diblock copolymer chain. The simulation results show that the introduction of the NP can induce phase separation of the originally disordered AB diblock copolymers, and phase diagrams as a function of the chain length ratio of A block and the attraction between A block and NP were constructed for the three giant surfactant systems. Via changing the location of NP from the end of B block to the AB-junction point and to the end of A block, the conformational entropies of the systems gradually decrease, leading to a significant difference in phase behaviors. When the NP is tethered to the end of B block, the giant surfactant system has the smallest phase-separation region in the phase diagram, and the resulting ordered structures have the smallest feature sizes. However, when the NP is tethered to the end of A block, the giant surfactant system has the largest phase-separation region, as well as the largest feature sizes of ordered structures. Moreover, the distributions of the NPs within microphase-separated domain can be well tailored by changing the chain length ratio of A block or the attraction between A block and NP in all of the three giant surfactant systems. These findings provide the guideline for the preparation of polymer-nanoparticle composites with controllable morphologies, desirable feature sizes, and precise NP distributions in experiments.

Self-assembly and structural manipulation of diblock-copolymer grafted nanoparticles in a homopolymer matrix

Detailed coarse-grained molecular dynamics simulations are performed to investigate the structural and mechanical properties of nanoparticles (NPs) grafted with an amphiphilic AB diblock copolymer, with the A-block being compatible with NPs and the B-block being miscible with a homopolymer matrix.

Computer simulation study on the self-assembly of tethered nanoparticles with tunable shapes

We built a tethered nanoparticle (TNP) model that is composed of a nanoparticle with a hydrophobic tethered polymer chain. The shape of the nanoparticle can be tuned from a pure rigid cube to a soft sphere, mimicking the increase of grafting density on the nanocube surfaces. With this model, we study the self-assembly of TNPs in dilute solution using a dissipative particle dynamics simulation technique, and especially focus on the influence of particle shape, tethered chain length, and grafting density on the self-assembly structures. Some intriguing aggregates such as spherical micelles, pearl-necklace-like structures, cubic columnar structures, handshake structures, core–shell–corona micelles, and four-patch micelles have been observed when varying the interactions between cubes and solvents and the lengths of tethered chain. Modifying the nanocube surface with some hydrophilic grafted chains helps the TNPs form small micelles. Increased steric repulsion due to chain overlapping at larger grafting densities results in shape transformation of the nanoparticle from a rigid cube to a soft sphere. In these cases, the self-assembled structures are characterized by the packing of nanoparticles on the micelle surface, and the typical packing mode turns from rectangular (typical for cubes) to hexagonal (typical for spheres).

The self-assembled structures are characterized by the packing of nanoparticles on the micelle surface, and the typical packing mode turns from rectangular (typical for cubes) to hexagonal (typical for spheres).

Crystallization-Driven Two-Dimensional Self-Assembly of Amphiphilic PCL-b-PEO Coated Gold Nanoparticles in Aqueous Solution

This Letter reports the first formation of free-standing plasmonic monolayer nanosheets by the self-assembly of AuNPs without assistance from a planar interface. The strategy involves the coating of poly(caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) diblock copolymers on AuNPs, followed by two-dimensional (2D) self-assembly of the resultant amphiphilic AuNPs in aqueous phase. The crystallization of the PCL blocks, affected by their grafting density and radius of gyration, drives the formation of the AuNP nanosheets, which undergoes a growth process of individual micelles to small nanosheets and eventually to large sheets. Due to the plasmonic coupling of AuNPs in close proximity, the AuNP nanosheets exhibit near-infrared (NIR) absorption with the maximum at about 700 nm. This study not only brings a new approach toward polymer-AuNP hybrid superstructures in solution, but also provides a new system for fundamental study on 2D self-assembly of AuNPs.

Cellular Internalization of Rod-Like Nanoparticles with Various Surface Patterns: Novel Entry Pathway and Controllable Uptake Capacity

The cellular internalization of rod-like nanoparticles (NPs) is investigated in a combined experimental and simulation study. These rod-like nanoparticles with smooth, abacus-like (i.e., beads-on-wires), and helical surface patterns are prepared by the cooperative self-assembly of poly(γ-benzyl-l-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) block copolymers and PBLG homopolymers. All three types of NPs can be internalized via endocytosis. Helical NPs exhibit the best endocytic efficacy, followed by smooth NPs and abacus-like NPs. Coarse-grained molecular dynamics simulations are used to examine the endocytic efficiency of these NPs. The NPs with helical and abacus-like surfaces can be endocytosed via novel "standing up" (tip entry) and "gyroscope-like" (precession) pathways, respectively, which are distinct from the pathway of traditional NPs with smooth surfaces. This finding indicates that the cellular internalization capacity and pathways can be regulated by introducing stripe patterns (helical and abacus-like) onto the surface of rod-like NPs. The results of this study may lead to novel applications of biomaterials, such as advanced drug delivery systems.

Extremely asymmetric phase diagram of homopolymer-monotethered nanoparticles: Competition between chain conformational entropy and particle steric interaction

The phase behaviors of homopolymer-monotethered nanoparticles (HMNs) in melt are investigated via a theoretical method combining self-consistent field theory for polymers and density functional theory for hard spheres. An extremely asymmetric phase diagram is observed: (i) microphases are only possible for the volume fraction of the tethered polymer f_A > 0.35; (ii) in addition to lamellar phase, the system can only self-assemble into various morphologies with a polymer-rich matrix, including gyroid phase, cylindrical phase, and spherical phase. In the frame of this theory, the critical point for HMNs' microphase separation is significantly lower than that of linear diblock copolymers. Furthermore, the characteristic length of microphase-separated structures of HMNs is much smaller than that of linear diblock copolymers with the same molecular weight. Our calculation results on morphologies and characteristic length agree well with recent simulations and experimental observations.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

The controllable construction and properties characterization of organic–inorganic hybrid materials based on benzoxazine-bridged polysilsesquioxanes

Some controllable morphology organic–inorganic hybrid materials have been prepared via the homopolymerization of benzoxazine-bridged polysilsesquioxanes precursors with different degrees of the triethoxysilane hydrolysis condensation.

Directed assembly of functionalized nanoparticles with amphiphilic diblock copolymers

We theoretically propose a simple approach to achieve soft nanoparticles with a self-patchiness nature, which are further directed to assemble into a rich variety of highly ordered superstructures.

Highly grafted polystyrene/polyvinylpyridine polymer gold nanoparticles in a good solvent: effects of chain length and composition

In this work, the structural features of spherical gold nanoparticles (NPs) decorated with highly grafted poly(styrene) (PS), poly(vinylpyridine) (PVP) and PS-PVP diblock copolymer brushes immersed in a good solvent are investigated by means of Dissipative Particle Dynamics (DPD) simulations as a function of grafted chain length and of homopolymer and copolymer chain composition. For NPs grafted either by PS or PVP homopolymer brushes (selected as a proof of concept), good agreement between the Daoud-Cotton theory, experimental evidence, and our DPD simulations is observed in the scaling behavior of single chain properties, especially for longer grafted chains, and in brush thickness prediction. On the other hand, for grafted chain lengths comparable to NP dimensions parabolic-like profiles of the end-monomer distributions are obtained. Furthermore, a region of high concentration of polymer segments is observed in the monomer density distribution for long homopolymers. In the case of copolymer-decorated NPs, the repulsion between PS and PVP blocks is found to substantially influence the radius of gyration and the shape of the end-monomer distribution of the relevant polymer shell. Moreover, for diblock chains, the un-swollen region is observed to be thinner (and, correspondingly, the swollen layer thicker) than that of a NP modified with a homopolymer of the same length. Finally, the lateral segregation of PS and PVP blocks is evidenced by our calculations and a detailed analysis of the corona behavior is reported, thus revealing the key parameters in controlling the surface properties and the response of diblock copolymer modified nanoparticles.

Tunable Affinity and Molecular Architecture Lead to Diverse Self-Assembled Supramolecular Structures in Thin Films

The self-assembly behavior of specifically designed giant surfactants is systematically studied in thin films using grazing incidence X-ray scattering and transmission electron microscopy, focusing on the effects of molecular nanoparticle (MNP) functionalities and molecular architectures on nanostructure formation. Two MNPs with different surface functionalities, i.e., hydrophilic carboxylic acid functionalized [60]fullerene (AC60) and omniphobic fluorinated polyhedral oligomeric silsesquioxane (FPOSS), are utilized as the head portions of the giant surfactants. By covalently tethering these functional MNPs onto the end point or junction point of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer, linear and star-like giant surfactants with different molecular architectures are constructed. With fixed length of the PEO block, changing the molecular weight of the PS block leads to the formation of various ordered phases and phase transitions. Due to the distinct affinity, the AC60-based and FPOSS-based giant surfactants form two- or three-component morphologies, respectively. A stretching parameter for the PS block is introduced to characterize the PS chain conformation in the different morphologies. The highly diverse self-assembled nanostructures with high etch resistance between components in small dimensions obtained from the giant surfactant thin films suggest that these macromolecules could provide a promising and robust platform for nanolithography applications.

Theoretical simulations of nanostructures self-assembled from copolymer systems

This article provides an overview of recent simulation investigations of the nanostructures and structure–property relationships in copolymer systems.

The effect of particle size on the morphology and thermodynamics of diblock copolymer/tethered-particle membranes

A combination of self-consistent field theory and density functional theory was used to examine the effect of particle size on the stable, 3-dimensional equilibrium morphologies formed by diblock copolymers with a tethered nanoparticle attached either between the two blocks or at the end of one of the blocks. Particle size was varied between one and four tenths of the radius of gyration of the diblock polymer chain for neutral particles as well as those either favoring or disfavoring segments of the copolymer blocks. Phase diagrams were constructed and analyzed in terms of thermodynamic diagrams to understand the physics associated with the molecular-level self-assembly processes. Typical morphologies were observed, such as lamellar, spheroidal, cylindrical, gyroidal, and perforated lamellar, with the primary concentration region of the tethered particles being influenced heavily by particle size and tethering location, strength of the particle-segment energetic interactions, chain length, and copolymer radius of gyration. The effect of the simulation box size on the observed morphology and system thermodynamics was also investigated, indicating possible effects of confinement upon the system self-assembly processes.

Controlling the localization of nanoparticles in assemblies of amphiphilic diblock copolymers

We performed a dissipative particle dynamics (DPD) approach to study the self-assembly of AB diblock copolymer tethered nanoparticles (P) in dilute solutions. Different morphological aggregates, including spherical micelles, vesicles, disk-like micelles and rod-like micelles, were found by varying the interaction between block copolymers and nanoparticles. Most importantly, the nanoparticles can selectively localize in the different domains within the aggregates. When the repulsive interaction between block copolymers and nanoparticles aPA = aPB = 25, the nanoparticles are evenly distributed within the spherical micelles. While aPA or aPB increases, the nanoparticles gradually aggregate and separate from copolymers and then localize in the central portion of vesicular wall or disk-like and rod-like micelles. The degree of stretching of the tethered copolymer chains gradually grows with the increase of aPA or aPB, while the degree of stretching of solvophobic block B decreases when the morphologies change from spherical to disk-like micelles and further to rod-like micelles. This work illustrates that tuning the miscibility of copolymers and nanoparticles could be used to project the selective localization of nanoparticles within the aggregates self-assembled by diblock copolymer tethered nanoparticles in dilute solutions.

Distinct mechanical properties of nanoparticle-tethering polymers

Nanoparticle-tethering polymers exhibit enhanced mechanical properties relative to neat polymers and nanoparticle/polymer blends.