Living Growth Kinetics of Polymeric Micelles on a Substrate.

Living growth of micelles on the substrate is an intriguing phenomenon; however, little is known about its growth kinetics, especially from a theoretical viewpoint. Here, we examine the living growth kinetics of polymeric micelles on a hydrophobic substrate immersed in an aqueous solution. The block copolymers first assemble into short cylinder seeds anchored on the substrate. Then, the small aggregates of block copolymers in the solutions fuse onto the active ends of the anchored seeds, leading to micelle growth on the substrate. A theoretical model is proposed to interpret such living growth kinetics. It is revealed that the growth rate coefficient on the substrate is independent of the copolymer concentration and the multistep feedings; however, it is significantly affected by the surface hydrophobicity. Brownian dynamics simulations further support the proposed growth mechanism and the kinetic model. This work enriches living assembly systems and provides guidance for fabricating bioinspired surface nanostructures.

Supramolecular Polymerization of Polymeric Nanorods Mediated by Block Copolymers.

Introducing a second component is an effective way to manipulate polymerization behavior. However, this phenomenon has rarely been observed in colloidal systems, such as polymeric nanoparticles. Here, we report the supramolecular polymerization of polymeric nanorods mediated by block copolymers. Experimental observations and simulation results illustrate that block copolymers surround the polymeric nanorods and mainly concentrate around the two ends, leaving the hydrophobic side regions exposed. These polymeric nanorods connect in a side-by-side manner through hydrophobic interactions to form bundles. As polymerization progresses, the block copolymers gradually deposit onto the bundles and finally assemble into helical nanopatterns on the outermost surface, which terminates the polymerization. It is anticipated that this work could offer inspiration for a general strategy of controllable supramolecular polymerization.

Self-Assembly of Copolymer Micelles: Higher-Level Assembly for Constructing Hierarchical Structure.

In recent years, the self-assembly of copolymer micelles has become an appealing frontier of supramolecular chemistry as a strategy to construct superstructures with multiple levels of complexity. The assembly of copolymer micelles is a form of higher-level self-assembly occurring at the nanoscale level where the building blocks are preassembled micelles. Compared to one-step hierarchical self-assembly, this assembly strategy is superior for manipulating multilevel architectures because the structures of the building blocks and higher-order hierarchies can be regulated separately in the first and higher-level assembly, respectively. However, despite the substantial advances in the self-assembly of copolymer micelles in recent years, universal laws have not been comprehensively summarized. This review article aims to provide an overview of the current progress and developing prospects of the self-assembly of copolymer micelles. In particular, the significant role of theoretical simulations in revealing the mechanism of copolymer micelle self-assembly is discussed.

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, it is shown that nanoparticle tethered block copolymers can self-assemble into hierarchically chiral nanostructures. Twofold 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.

Distinctive Dielectric Permittivity of Hierarchical Nanostructures with Ordered Nanoparticle Networks Self-Assembled from AB-g-NP/AC Block Copolymer Mixtures.

Directing nanoparticles into ordered organization in polymer matrix to improve macroscopic properties of nanocomposites remains a challenge. Herein, by means of theoretical simulations, we show the high permittivity of hybrid nanostructures designed with mixtures of AB block copolymer-grafted nanoparticles and lamella-forming AC diblock copolymers. The grafted nanoparticles self-assemble into parallel stripes or highly ordered networks in the lamellae of the AC diblock copolymers. The ordered nanoparticle networks, including honeycomb-like and kagomé networks, provide bending and conductive pathways for concentrating electric fields, which results in the improvement of the permittivity. We envisage that this strategy will open a gateway to prepare hierarchically ordered functional nanocomposites with distinctive dielectric properties.

Membrane Nanopores Induced by Nanotoroids via an Insertion and Pore-Forming Pathway.

The formation of membrane nanopores is one of the crucial activities of cells and has attracted considerable attention. However, the understanding of their types and mechanisms is still limited. Herein, we report a novel nanopore formation phenomenon achieved through the insertion of polymeric nanotoroids into the cellular membrane. As revealed by theoretical simulations, the nanotoroid can embed in the membrane, leaving a nanopore on the cell. The through-the-cavity wrapping of lipids is critical for the retention of the nanotoroid in the membrane, which is attributed to both a relatively large inner cavity of the nanotoroid and a moderate attraction between the nanotoroid and membrane lipids. Under the guidance of the simulation predictions, experiments using polypeptide toroids as pore-forming agents were performed, confirming the unique biophysical phenomenon. This work demonstrates a distinctive pore-forming pathway, deepens the understanding of the membrane nanopore phenomenon, and assists in the design of advanced pore-forming materials.

Anchorage-Dependent Living Supramolecular Self-Assembly of Polymeric Micelles.

Anchorage-dependent contact-inhibited growth usually refers to on-surface cell proliferation inhibited by the proximity of other cells. This phenomenon, prominent in nature, has yet to be achieved with polymeric micelles. Here, we report the control living supra-macromolecular self-assembly of elongated micelles with a liquid crystalline core onto a hydrophobic substrate via the synergetic interactions between the substrate and aggregates dispersed in solution. In this system, seed formation is a transient phenomenon induced by the adsorption and rearrangement of the core-swollen aggregates. The seeds then trigger the growth of elongated micelles onto the substrate in a living controllable manner until the contact with the substrate is disrupted. Brownian dynamic simulations show that this unique behavior is due to the fusion of the aggregates onto both ends of the anchored seeds. More important, the micelle length can be tuned by varying the substrate hydrophobicity, a key step toward the fabrication of intricate structures.

Programmable Morphology Evolution of Rod-Coil-Rod Block Copolymer Assemblies Induced by Variation of Chain Ordering.

Morphology transition of block copolymer assemblies in response to external stimuli has attracted considerable attention. However, our knowledge about the mechanism of such a transition is still limited, especially for rod-coil block copolymers. Here, we report a programmable morphology evolution of assemblies induced by variation of chain ordering for rod-coil-rod triblock copolymers. A sequence of morphology transition from ellipsoids to disks, bowls, and vesicles is observed by increasing the solution temperature. At high temperatures, the mobility of the rod chain increases and the rigidity of the rod chain decreases. This gives rise to an ellipsoid-to-vesicle morphology transition. Dissipative particle dynamics theoretical simulations were performed to reveal the mechanism of this morphology transition process. It was found that the increase of rod chain mobility and the decrease of rod chain rigidity induce a decrease of chain ordering of rod blocks as temperature increases, which results in an ellipsoid-to-vesicle morphology transition. The gained information can guide the construction of nanoassemblies based on the rod-coil block copolymers.

A theoretical insight into the curing mechanism of phthalonitrile resins promoted by aromatic amines.

High-temperature phthalonitrile resins have a wide range of applications, and understanding their curing mechanism is of great importance for academic research and engineering applications. However, the actual curing mechanism is still elusive. We presented a density functional theory study on the curing mechanism of phthalonitrile resins promoted by aromatic amines using phthalonitrile and aniline as the model compounds. We found that the rate-determining step is the initial nucleophilic addition of amines with nitrile groups on phthalonitrile to generate an amidine intermediate. The amines play a vital role in the H-transfer promoter throughout the curing reaction. The amidine and isoindoline are the critical intermediates, which can readily react with phthalonitrile through 6-membered transition states. The intramolecular cyclization of amidine intermediates is the vital step in forming isoindoline intermediates, which can be significantly promoted by amines. The proposed curing reaction pathways are kinetically more favorable than the previously reported ones, which can account for the formation of triazine, polyisoindoline, and phthalocyanine and provide a molecular-level understanding of the curing reaction.

Effect of curing reaction types on the structures and properties of acetylene-containing thermosets: towards optimization of curing procedure.

High-temperature thermosets are usually prepared from resins containing alkynyl groups, and their properties depend much upon the curing process containing various types of curing reactions. However, how the curing process affects the properties remains unclear due to the complicated curing reactions. We used molecular dynamics simulations to investigate the effect of curing reaction types, including cyclotrimerization, Diels-Alder reaction, and radical reaction, on the structures and properties of imide oligomers terminated with alkynyl groups. The results show that the cycloadditions such as cyclotrimerization and Diels-Alder reaction endow the thermosets with rigid structures and high moduli. Compared with the cycloadditions, the radical reaction enables the formation of flexible cured structures, which can enhance the toughness of thermosets. The differences in thermal and mechanical properties caused by different curing types were elucidated by the relaxation processes of fragments in these cured systems and were explained by the variation of torsion energy in different curing forms. As this work aims to optimize the curing procedure to obtain high-performance resins with desired properties, different curing procedures were finally designed according to the theoretical studies, and the obtained cured polymers show significant differences in the properties from different curing ways. The results can guide the preparation of desired thermosetting resins by tuning the curing procedure.

Distinctive Optical Properties of Hierarchically Ordered Nanostructures Self-Assembled from Multiblock Copolymer/Nanoparticle Mixtures.

Hybrid materials with hierarchical nanostructures are of great interest for their advanced functions. However, the effect of the formation of hierarchical nanostructures on properties is not well understood. Here, through combining dissipative particle dynamics simulation and the finite-difference time-domain method, the optical properties of hierarchically ordered nanostructures formed by mixtures of A(BC)n multiblock copolymers and nanoparticles (NPs) are investigated. A series of hierarchically ordered nanostructures with multiple small-length-scale hybrid domains are obtained from the self-assembly of A(BC)n /NP. An increase and blueshift in optical absorption are observed when the number of small-length-scale hybrid domains increases. The small-length-scale hybrid domains enhance light scattering, which consequently contributes to the improved optical performance. These findings can yield guidelines for designing hierarchically ordered functional nanocomposites with light-harvesting characteristics.

2D Chiral Stripe Nanopatterns Self-Assembled from Rod-Coil Block Copolymers on Microstripes.

Chiral nanoarchitectures usually possess unique and intriguing properties. However, the construction of 2D chiral nanopatterns through polymer self-assembly is a challenge. Reported herein is the formation of chiral stripe nanopatterns through surface self-assembly of polypeptide-based rod-coil block copolymers on microstripes. The nanostripes align oblique to the boundary of the microstripes, resulting in the chirality of the nanopatterns. The chirality of the nanopatterns is closely related to the width of the microstripes, i.e., a narrower width results in higher chirality. Besides, the chiral sense of the nanopatterns can be regulated by the chirality of the polypeptide blocks. This work demonstrates the transmission of chirality from polymer to nanoarchitecture on a confined surface, which can guide the preparation of nanopatterns with tuned chiral features.

Theoretical study on thermal curing mechanism of arylethynyl-containing resins.

Arylethynyl reactive groups have been widely used in high-temperature polymers, and therefore, understanding their curing mechanism is of great importance for academic research and engineering applications. However, no consensus has been achieved on the actual curing mechanism of arylethynyl-containing resins so far. Herein, we present a density functional theory study on the thermal curing mechanism of arylethynyl-containing resins using phenylacetylene and diphenylacetylene as model compounds. It was discovered that the rate-determining step is the dimerization of arylacetylenes into diradical intermediates. The possibilities of the Straus-type intermediates and concerted Diels-Alder cycloaddition between two arylacetylenes can be ruled out. Cyclobutadiene and cyclic allene are the critical intermediates generated by the intramolecular coupling of diradicals. The formation of polyene is preferred by monoradical initiation rather than diradical growth. The overall reaction pathways can well account for the formation of naphthalenic dimers, benzenic trimers, and polyenic chains. The computational results of reactivity for the dimerization of arylacetylenes were finally compared with the existing experimental findings, and an agreement is shown.

Living Supramolecular Polymerization of Rod-Coil Block Copolymers: Kinetics, Origin of Uniformity, and Its Implication.

We conduct Brownian dynamics simulations to explore the kinetics of living supramolecular polymerization using seeded growth of rod-coil block copolymers as a model system. We model the kinetics of supramolecular polymerization by developing kinetic theory for classical living covalent polymerization with length-dependent rate coefficients. The rate coefficient in the proposed kinetics theory decreases with increasing cylindrical micelle length, which is attributed to micelle rigidity and unique diffusion behavior. Like living covalent polymerization, living supramolecular polymerization can produce low-dispersity assemblies with rigidity via different mechanisms. The results nicely explain the available experimental observations.

Helical Toroids Self-Assembled from a Binary System of Polypeptide Homopolymer and its Block Copolymer.

Toroids and helices are fundamental geometrical structures in nature. Polymers can self-assemble into various nanostructures, including both toroids and helices; however, nanostructures combining toroidal and helical morphologies (that is, helical toroids) are rarely observed. A binary system is reported containing polypeptide homopolymer and its block copolymer, which can hierarchically self-assemble into uniform helical nanotoroids in solution. The formation of the helical toroids is a successive two-step process. First, the homopolymers aggregate into fibrils and convolve into toroids, thereby resembling the toroidal condensation of deoxyribonucleic acid (DNA) chains. Second, the block copolymers self-assemble on the homopolymer toroids and result in helical surface patterns. Additionally, the chirality of the surface helical patterns can be varied by the chirality of the polypeptide block copolymers.

Reversible Polymerization-like Kinetics for Programmable Self-Assembly of DNA-Encoded Nanoparticles with Limited Valence.

A similarity between the polymerization reaction of molecules and the self-assembly of nanoparticles provides a unique way to reliably predict structural characteristics of nanoparticle ensembles. However, the quantitative elucidation of programmable self-assembly kinetics of DNA-encoded nanoparticles is still challenging due to the existence of hybridization and dehybridization of DNA strands. Herein, a joint theoretical-computational method is developed to explicate the mechanism and kinetics of programmable self-assembly of limited-valence nanoparticles with surface encoding of complementary DNA strands. It is revealed that the DNA-encoded nanoparticles are programmed to form a diverse range of self-assembled superstructures with complex architecture, such as linear chains, sols, and gels of nanoparticles. It is theoretically demonstrated that the programmable self-assembly of DNA-encoded nanoparticles with limited valence generally obeys the kinetics and statistics of reversible step-growth polymerization originally proposed in polymer science. Furthermore, the theoretical-computational method is applied to capture the programmable self-assembly behavior of bivalent DNA-protein conjugates. The obtained results not only provide fundamental insights into the programmable self-assembly of DNA-encoded nanoparticles but also offer design rules for the DNA-programmed superstructures with elaborate architecture.

The Special "Morse Code" between Solvent Polarity and Morphology Flexibility in a POSS-Dendrimer Supramolecular System.

An amazing phenomenon of the relative magnitude of modulus of two liquid-crystal (LC) gels is found inverted under/above their phase transition temperature TLC-iso , which is further proved to be caused by their diverse morphology flexibility. By testing the polarity of two LCs, gelator POSS-G1-Boc (POSS=polyhedral oligomeric silsesquioxane) was discovered to self-assemble into more flexible structures in a relatively low polar LC, whereas more rigid ones are formed in higher polar LC. Hence, a fitting function to connect morphology flexibility with solvent polarity was established, which can even be generalized to a number of common solvents. Experimental observations and coarse-grained molecular dynamics simulations revealed that solvent polarity mirrors a "Morse code", with each "code" corresponding to a specific morphology flexibility.

Customizing topographical templates for aperiodic nanostructures of block copolymers via inverse design.

The limited complexity of self-assembled nanostructures of block copolymers seriously impedes their potential utility in the semiconductor industry. Therefore, the customizability of complex nanostructures has been a long-standing goal for the utilization of directed self-assembly in nanolithography. Herein, we integrated an advanced inverse design algorithm with a well-developed theoretical model to deduce inverse solutions of topographical templates to direct the self-assembly of block copolymers into reproducible target structures. The deduced templates were optimized by finely tuning the input parameters of the inverse design algorithm and through symmetric operation as well as nanopost elimination. More importantly, our developed algorithm has the capability to search inverse solutions of topographical templates for aperiodic nanostructures over exceptionally large areas. These results reveal design rules for guiding templates for the device-oriented nanostructures of block copolymers with prospective applications in nanolithography.

Distinctive phase separation dynamics of polymer blends: roles of Janus nanoparticles.

Janus nanoparticles (JPs), which are anisotropic nanoparticles with at least two opposite surface regions, have been demonstrated as highly efficient compatibilizers for polymer blends. However, there are still a number of open questions concerning the mechanism behind the influence of JPs on the phase separation dynamics of polymer blends. Herein, we report a counter-intuitive feature of JPs concerning their roles during spinodal decomposition (SD); that is, they promote the decomposition of unlike polymers in the early stage of SD but retard it during the late stage. This is in remarkable contrast to traditional compatibilizers such as block copolymers and homogenous nanoparticles, which impede phase separation during both stages. We further demonstrate that the unique promoting effect of JPs at early times is due to the formation of microphase-separated homopolymer-rich regions in the vicinity of opposite JP surface regions. Our findings are expected to have important implications for the phase separation behavior of JP-compatibilized polymer blends, whose morphologies and performance could be controlled by tuning the interactions between the constituent polymers and JP-based compatibilizers.

Chain-Conformation-Directed Polymerization Cyclization for Effective Synthesis of Macrocycles in Bulk.

Biological cyclization is highly efficient, and this can be attributed to the conformation of the backbone of the biopolymer. Taking advantage of metal-coordination geometry, we developed a method for conformation-directed polymerization cyclization through rational design of metal carbonyl monomers that could be used to produce cyclic macromolecules, even in bulk. P FpR [P Fp=(PPh2 (CH2 )3 Cp)Fe(CO)2 with the phosphine group tethered on the cyclopentadiene (Cp) ring; R=CH3 or (CH2 )5 CH3 ] was designed and synthesized for migration insertion polymerization to generate P(P FpR) with the polymer backbone containing Cp-Fe bonds. Growth of the backbone led to a cyclic conformation with close end-to-end distances, which facilitated the cyclization. This conformation-directed cyclization was attributed to the piano-stool metal-coordination geometry of the repeating units and the low rotational barrier of the Cp-Fe bonds in the backbone. The produced macrocycles, which contain a metal carbonyl coordination structure in their backbones, are rigid, unlike many organic macrocycles. The macrocycles thus have a large excluded volume. This new type of metal carbonyl macrocycle will be of interest as a building block for supramolecular chemistry and in the exploration of novel materials.