Head-Tail Asymmetry as the Determining Factor in the Formation of Polymer Cubosomes or Hexasomes in a Rod-Coil Amphiphilic Block Copolymer

Multi-Responsive Peptide-Based Ultrathin Nanosheets Prepared by a Horizontal Monolayer Assembly

In this study, peptide-based self-assembled nanosheets with a thickness of approximately 1 nm were prepared using a hierarchical covalent physical fabrication strategy. The covalent alternating polymerization of helical peptide E3 with an azobenzene (AZO) structure yielded copolymers CoP(E3-AZO), which physically self-assembled into ultrathin nanosheets in an unanticipated two-dimensional horizontal monolayer arrangement. This special monolayer arrangement enabled the thickness of the nanosheets to be equal to the cross-sectional diameter of a single linear copolymer, which is a rare phenomenon. Molecular dynamics simulations suggested that the synergistic effect of multiple molecular interactions drives the self-assembly of CoP(E3-AZO) into nanosheets and that various methods, including phototreatment, pH adjustment, the addition of additives, and introduction of cosolvents, can alter the molecular interactions and modulate the self-assembly of CoP(E3-AZO), yielding diverse nanostructures. Remarkably, the ultrathin nanosheets selectively inhibited cancer cells at certain concentrations.

A Versatile Synthesis Platform Based on Polymer Cubosomes for a Library of Highly Ordered Nanoporous Metal Oxides Particles

Polymer cubosomes (PCs) have well-defined inverse bicontinuous cubic mesophases formed by amphiphilic block copolymer bilayers. The open hydrophilic channels, large periods, and robust physical properties of PCs are advantageous to many host-guest interactions and yet not fully exploited, especially in the fields of functional nanomaterials. Here, the self-assembly of poly(ethylene oxide)-block-polystyrene block copolymers is systematically investigated and a series of robust PCs is developed via a cosolvent method. Ordered nanoporous metal oxide particles are obtained by selectively filling the hydrophilic channels of PCs via an impregnation strategy, followed by a two-step thermal treatment. Based on this versatile PC platform, the general synthesis of a library of ordered porous particles with different pore structures3 ¯ $\bar{3}$ 3 ¯ $\bar{3}$ , tunable large pore size (18-78 nm), high specific surface areas (up to 123.3 m2 g-1 for WO3) and diverse framework compositions, such as transition and non-transition metal oxides, rare earth chloride oxides, perovskite, pyrochlore, and high-entropy metal oxides is demonstrated. As typical materials obtained via this method, ordered porous WO3 particles have the advantages of open continuous structure and semiconducting properties, thus showing superior gas sensing performances toward hydrogen sulfide.

Photocleavable Polymer Cubosomes: Synthesis, Self-Assembly, and Photorelease

Polymer cubosomes (PCs) are a recent class of self-assembled block copolymer (BCP) microparticles with an accessible periodic channel system. Most reported PCs consist of a polystyrene scaffold, which provides mechanical stability for templating but has a limited intrinsic functionality. Here, we report the synthesis of photocleavable BCPs with compositions suitable for PC formation. We analyze the self-assembly mechanism and study the model release of dyes during irradiation, where the transition of the BCPs from amphiphilic to bishydrophilic causes the rapid disassembly of the PCs. A combination of modeling and experiment shows that the evolution of PCs proceeds first via liquid-liquid phase separation into polymer-rich droplets, followed by microphase separation within this droplet confinement, and finally, membrane reorganization into high internal order. This insight may encourage exploration of alternative preparation strategies to better control the size and homogeneity of PCs.

Increasing the Accessibility of Internal Catalytic Sites in Covalent Organic Frameworks by Introducing a Bicontinuous Mesostructure

Introducing continuous mesochannels into covalent organic frameworks (COFs) to increase the accessibility of their inner active sites has remained a major challenge. Here, we report the synthesis of COFs with an ordered bicontinuous mesostructure, via a block copolymer self-assembly-guided nanocasting strategy. Three different mesostructured COFs are synthesized, including two covalent triazine frameworks and one vinylene-linked COF. The new materials are endowed with a hierarchical meso/microporous architecture, in which the mesochannels exhibit an ordered shifted double diamond (SDD) topology. The hierarchically porous structure can enable efficient hole-electron separation and smooth mass transport to the deep internal of the COFs and consequently high accessibility of their active catalytic sites. Benefiting from this hierarchical structure, these COFs exhibit excellent performance in visible-light-driven catalytic NO removal with a high conversion percentage of up to 51.4 %, placing them one of the top reported NO-elimination photocatalysts. This study represents the first case of introducing a bicontinuous structure into COFs, which opens a new avenue for the synthesis of hierarchically porous COFs and for increasing the utilization degree of their internal active sites.

Encounter between Gyroid and Lamellae in Janus Colloidal Particles Self-Assembled by a Rod-Coil Block Copolymer

Controlling the internal structure of block copolymer (BCP) particles has a significant influence on its functionalities. Here, a structure-controlling method is proposed to regulate the internal structure of BCP Janus colloidal particles using different surfactants. Different microphase separation processes take place in two connected halves of the Janus particles. An order-order transition between gyroid and lamellar phases is observed in polymeric colloids. The epitaxial growth during the structural transformation from gyroid to lamellar phase undergoes a two-layered rearrangement to accommodate the interdomain spacing mismatch between these two phases. This self-assembly behavior can be ascribed to the preferential wetting of BCP chains at the interface, which can change the chain conformation of different blocks. The Janus colloidal particles can further experience a reversible phase transition by restructuring the polymer particles under solvent vapor. It is anticipated that the new phase behavior found in Janus particles can not only enrich the self-assembly study of BCPs but also provide opportunities for various applications based on Janus particles with ordered structures.

Block Copolymer Self-Assembly Directed Synthesis of Porous Materials with Ordered Bicontinuous Structures and Their Potential Applications

Porous materials with their ordered bicontinuous structures have attracted great interest owing to ordered periodic structures as well as 3D interconnected network and pore channels. Bicontinuous structures may favor efficient mass diffusion to the interior of materials, thus increasing the utilization ratio of active sites. In addition, ordered bicontinuous structures confer materials with exceptional optical and magnetic properties, including tunable photonic bandgap, negative refraction, and multiple equivalent magnetization configurations. The attractive structural advantages and physical properties have inspired people to develop strategies for preparing bicontinuous-structured porous materials. Among a few synthetic approaches, the self-assembly of block copolymers represents a versatile strategy to prepare various bicontinuous-structured functional materials with pore sizes and lattice parameters ranging from 1 to 500 nm. This article overviews progress in this appealing area, with an emphasis on the synthetic strategies, the structural control (including topologies, pore sizes, and unit cell parameters), and their potential applications in energy storage and conversion, metamaterials, photonic crystals, cargo delivery and release, nanoreactors, and biomolecule selection.

Regulation of the nanostructures self-assembled from an amphiphilic azobenzene homopolymer: influence of initial concentration and solvent solubility parameter

The control over the morphology and nanostructure of soft nanomaterials self-assembled from amphiphilic polymers is of high interest, but is still challenging. Herein, we manipulate the morphology of bowl-shaped nanoparticles by changing initial polymer concentrations, and prepare nanotubes and nanowires, both twisted and not, by using solvents with different solubility parameters. An amphiphilic azobenzene homopolymer (poly(4-(phenyldiazenyl)phenyl methacrylamide), PAzoMAA) is designed and synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization, which can self-assemble into bowl-shaped nanoparticles promoted by the synergy of hydrogen bonding and π-π interaction. More significantly, the opening size of the bowl-shaped nanoparticles can be controlled by changing initial polymer concentrations. Nanotubes and nanowires, both twisted and not, are also obtained using a solvothermal method in alcohols. The relationship between the structure of the nanomaterials and the solubility parameters of the alcohols is investigated, revealing the molecular arrangement patterns of PAzoMAA in different nanostructures. Overall, we propose a facile strategy to manipulate the microstructure of bowl-shaped nanoparticles and one-dimensional nanomaterials by adjusting initial polymer concentration and solvent solubility parameters. Our study may bring new avenues for controlling the nanostructures of soft nanomaterials.

Formation and Transformation of Polystyrene-block-poly(2-vinylpyridine) Hexasomes in the Solvent Exchange

The generation of inverse micellar nanostructures, especially those with open channels, using commercially available diblock copolymers (BCP), is vital for their wide applications in drug delivery and catalyst templating. However, the rigid requirements for forming inverse morphologies, such as the highly asymmetric molecular structures, the semicrystalline motifs, and concentrated solutions of diblock copolymers, represent obstacles to the development of successful strategies. In this study, the inverse polystyrene-block-poly(2-vinylpyridine) (PS_30K-b-P2VP_8.5K) micelles, i.e., the hexasomes with p6mm lattice, were generated through a modified solvent exchange via adding d-tartaric acid (d-TA) in the nonsolvent. Various intermediate morphologies have been identified with the change of d-TA concentration. Interestingly, in the high d-TA concentration (∼20 mg/mL), the hexasomes with close-packed hoops changed to mesoporous spheres with regularly packed perpendicular cylindrical channels (V_D-TA: V_BCP 6:100), and further to the mesoporous spheres with gyri-like open pores (V_D-TA: V_BCP > 15:100) with the increasing acidity in the mixed solvent. This study presents a simple and economical pathway for fabricating PS_30K-b-P2VP_8.5K hexasomes and first demonstrates these hexasomes can be modified to the morphology with open channels that will benefit their further applications.

Dynamic Coassembly of Amphiphilic Block Copolymer and Polyoxometalates in Dual Solvent Systems: An Efficient Approach to Heteroatom-Doped Semiconductor Metal Oxides with Controllable Nanostructures

Dynamic coassembly of block copolymers (BCPs) with Keggin-type polyoxometalates (POMs) is developed to synthesize heteroatom-doped tungsten oxide with controllable nanostructures, including hollow hemispheres, nanoparticles, and nanowires. The versatile coassembly in dual n-hexane/THF solvent solution enables the fomation of poly(ethylene oxide)-b-polystyrene (PEO-b-PS)/POMs (e.g., silicotungstic acid, H₄SiW₁₂O₄₀) nanocomposites with different morphologies such as spherical vesicles, inverse spherical micelles, and inverse cylindrical micelles, which can be readily converted into diverse nanostructured metal oxides with high surface area and unique properties via in situ thermal-induced structural evolution. For example, uniform silicon-doped WO₃ (Si-WO₃) hollow hemispheres derived from coassembly of PEO-b-PS with H₄SiW₁₂O₄₀ were utilized to fabricate gas sensing devices which exhibit superior gas sensing performance toward acetone, thanks to the selective gas-solid interface catalytic reaction that induces resistance changes of the devices due to the high specific surface areas, abundant oxygen vacancies, and the Si-doping induced metastable ε-phase of WO₃. Furthermore, density functional theory (DFT) calculation reveals the mechanism about the high sensitivity and selectivity of the gas sensors. On the basis of the as-fabricated devices, an integrated gas sensor module was constructed, which is capable of real-time monitoring the environmental acetone concentration and displaying relevant sensing results on a smart phone via Bluetooth communication.

Porous Polymer Cubosomes with Ordered Single Primitive Bicontinuous Architecture and Their Sodium-Iodine Batteries

Bicontinuous porous materials, which possess 3D interconnected pore channels facilitating a smooth mass transport, have attracted much interest in the fields of energy and catalysis. However, their synthesis remains very challenging. We report a general approach, using polymer cubosomes as the template, for the controllable synthesis of bicontinuous porous polymers with an ordered single primitive (SP) cubic structure, including polypyrrole (SP-PPy), poly-m-phenylenediamine (SP-PmPD), and polydopamine (SP-PDA). Specifically, the resultant SP-PPy had a unit cell parameter of 99 nm, pore diameter of 45 nm, and specific surface area of approximately 60 m²·g^-1. As a proof of concept, the I₂-adsorbed SP-PPy was employed as the cathode materials of newly emerged Na-I₂ batteries, which delivered a record-high specific capacity (235 mA·h·g^-1 at 0.5 C), excellent rate capability, and cycling stability (with a low capacity decay of 0.12% per cycle within 400 cycles at 1 C). The advantageous contributions of the bicontinuous structure and I₃^- adsorption mechanism of SP-PPy were revealed by a combination of ion diffusion experiments and theoretical calculations. This study opens a new avenue for the synthesis of porous polymers with new topologies, broadens the spectrum of bicontinuous-structured materials, and also develops a novel potential application for porous polymers.

Self-Assembly of Polystyrene-b-poly(2-vinylpyridine)/Chloroauric Acid at the Liquid/Liquid Interface

The self-assembly of polystyrene-block-poly(2-vinylpyridine) at the liquid/liquid interface has been systematically investigated to develop a series of primary morphologies of the aggregates. The block copolymers self-assembled into large areas of nanodot arrays, parallel nanostrands, layered films, parallel nanobelts, honeycomb monolayers, and foams by reacting with chloroauric acid, depending on the molecular structure of the block copolymers and the amount of chloroauric acid. The formation of the first four ordered structures resulted from interfacial adsorption and self-assembly, and nucleation and epitaxial growth. The latter two structures were attributed to the water hole templating effect and spontaneous interfacial emulsification, respectively. This work provides insight into the self-assembly behavior of block copolymers at the interface and provides a facile approach for fabricating functional structures.

Selective sequential infiltration synthesis of ZnO in the liquid crystalline phase of silicon-containing rod-coil block copolymers

The combination of block copolymer (BCP) thin film self-assembly and selective infiltration synthesis of inorganic materials into one BCP block provides access to various organic-inorganic hybrids. Here, we apply sequential infiltration synthesis, a vapor-phase hybridization technique, to selectively introduce ZnO into the organic microdomains of silicon-containing rod-coil diblock copolymers and a triblock terpolymer, polydimethylsiloxane (PDMS)-b-poly{2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene} (PDMS-b-PMPCS) and PDMS-b-polystyrene-b-PMPCS (PDMS-b-PS-b-PMPCS), in which the PMPCS rod block is a liquid crystalline polymer. The in-plane cylindrical PDMS-b-PMPCS and core-shell cylindrical and hexagonally perforated lamellar PDMS-b-PS-b-PMPCS films were infiltrated with ZnO with high selectivity to the PMPCS. The etching contrast between PDMS, PS and the ZnO-infused PMPCS enables the fabrication of ZnO/SiO_x binary composites by plasma etching and reveals the core-shell morphology of the triblock terpolymer.

Effect of hydrophilic block end groups and block junction on block copolymer self-assembly in solution

Recent research suggests that the end groups of polymers can affect their self-assembly.

Photoluminescent polymer cubosomes prepared by RAFT-mediated polymerization-induced self-assembly

The preparation of photoluminescent polymer assemblies with a wide range of morphologies, including spongosomes and cubosomes, via an efficient RAFT-mediated polymerization-induced self-assembly (RAFT-PISA) process, was demonstrated.

Polymerization-Induced Hierarchical Self-Assembly: From Monomer to Complex Colloidal Molecules and Beyond

The nanoscale hierarchical design that draws inspiration from nature's biomaterials allows the enhancement of material performance and enables multifarious applications. Self-assembly of block copolymers represents one of these artificial techniques that provide an elegant bottom-up strategy for the synthesis of soft colloidal hierarchies. Fast-growing polymerization-induced self-assembly (PISA) renders a one-step process for the polymer synthesis and in situ self-assembly at high concentrations. Nevertheless, it is exceedingly challenging for the fabrication of hierarchical colloids via aqueous PISA, simply because most monomers produce kinetically trapped spheres except for a few PISA-suitable monomers. We demonstrate here a sequential one-pot synthesis of hierarchically self-assembled polymer colloids with diverse morphologies via aqueous PISA that overcomes the limitation. Complex formation of water-immiscible monomers with cyclodextrin via "host-guest" inclusion, followed by sequential aqueous polymerization, provides a linear triblock terpolymer that can in situ self-assemble into hierarchical nanostructures. To access polymer colloids with different morphologies, three types of linear triblock terpolymers were synthesized through this methodology, which allows the preparation of AX_n-type colloidal molecules (CMs), core-shell-corona micelles, and raspberry-like nanoparticles. Furthermore, the phase separations between polymer blocks in nanostructures were revealed by transmission electron microscopy and atomic force microscopy-infrared spectroscopy. The proposed mechanism explained how the interfacial tensions and glass transition temperatures of the core-forming blocks affect the morphologies. Overall, this study provides a scalable method of the production of CMs and other hierarchical structures. It can be applied to different block copolymer formulations to enrich the complexity of morphology and enable diverse functions of nano-objects.

Recent Progress in Polymer Cubosomes and Hexosomes

Polymer cubosomes and hexosomes are polymer colloids with inverted lyotropic liquid crystal phases as internal structures. They are composed of regular networks of water-filled channels surrounded by a bilayer membrane made from amphiphilic block copolymers. Due to the uniform, tunable, and highly ordered porous structure, polymer cubosomes and hexosomes present numerous advantages over polymer micelles and vesicles, such as the high loading volumes for both hydrophilic and hydrophobic substances, large specific surface areas, and good mechanical and chemical stabilities. The polymer chemistry also enables unlimited molecular design to endow these polymer colloids with a lot of adjustable physical and chemical properties. Therefore, polymer cubosomes and hexosomes have attracted increasing attention for their potential applications in materials science and nanotechnology. This review outlines the recent progress in this field with an emphasis on the polymer architectures, the self-assembly conditions and mechanisms, and some application examples which are special for these inverted polymer colloids. It is hoped to provide some practical guidance for researchers interested in polymer cubosomes and hexosomes.

Inverse Bicontinuous Structure by Polymerization-Induced Self-Assembly Against Single-Chain Nanoparticles

Polymer particles with inverse bicontinuous structures have attracted considerable attention due to their diverse applications. The conventional generation requires controlling numerous key parameters under strict conditions, such as solvent property, polymer composition, and architecture. In order to improve the preparation efficiency within a broad window, we employed a method by polymerization-induced self-assembly (PISA) against intramolecularly folded single-chain nanoparticles (SCNPs). The SCNPs bear an active site for further polymerization. The SCNPs with smaller sizes facilitate easier controlling of the packing parameter above unity to meet the requirement of the unique structures. The concept is demonstrated by forming the inverse bicontinuous structure through PISA in ethanol against two SCNPs of P4VP(SCNP_x%)₃₅-CTA and P(PEGMA₂₀-co-TMSPMA₄)(SCNP_16.7%)-CTA. The unique structure is easily achieved when growing a relatively shorter polymer chain within a broad window. The work paves the avenue to prepare polymer particles with the unique structure in large scale, and other functional materials are expected by using the functional SCNPs or favorable growth of desired materials within the particles.

Triggered Degradable Colloidal Particles with Ordered Inverse Bicontinuous Cubic and Hexagonal Mesophases

We herein report a facile strategy to prepare triggered degradable block copolymer nano/macro-objects, ranging from typical micelles, worms, jellyfish, and vesicles to rarely achieved spongosomes, cubosomes, and hexosomes via RAFT-mediated polymerization-induced self-assembly (PISA). The morphological transitions from a simple spherical micelle to a spongosome, ordered Im3¯m cubosome, and p6mm hexosome were captured and demonstrated by TEM, SEM, and synchrotron SAXS. In addition, morphological phase diagrams including important factors, such as solid contents, degree of polymerization (DP), and stabilizer block chain length, were constructed to unveil the formation mechanism and guide the scalable preparation of complex morphologies with packing parameter (P) > 1. This study not only represents an example that achieved inverse mesophases via acrylate-based monomers with high conversion but also reports a triggered degradable system in the most extended morphological range via PISA. The facile synthesis and stimuli-responsiveness of our system should greatly expand the utility of polymer inverse mesophases for triggered releasing, templating, and many other applications.

Efficient Access to 3D Mesoscopic Prisms in Polymeric Soft Materials

The preparation of 3D functional isolated mesoscopic assemblies remains a challenge in the self-assembly of polymers. Here, well-defined 3D hexagonal and hexagram prisms with uniform dimensions are acquired by the crystallization of the inclusion complex composed of a crystalline molecule tris-o-phenylenedioxycyclotriphosphazene (TPP) and a block copolymer. The crystalline TPP plays an important role in the self-assembling process. The faceted morphologies of the hexagonal and hexagram prisms are infrequent in the self-assembly field of soft materials. The formation of the prisms experiences a 3D growth mechanism. The epitaxial growth, accompanied by the heterogeneous nucleation in the edges, yields the growth of inclusion crystals. This study provides a path to construct well-defined polymeric soft materials with broad utility based on numerous supramolecular complexes.

Bending Behavior and Directed Self-Assembly of Rod-Coil Block Copolymers

The formation of zigzags, chevrons, Y-junctions, and line segments is demonstrated in thin films formed from cylindrical morphology silicon-containing conformationally asymmetric rod-coil diblock copolymers and triblock terpolymers under solvent annealing. Directed self-assembly of the block copolymers within trenches yields well-ordered cylindrical microdomains oriented either parallel or transverse to the sidewalls depending on the chemical functionalization of the sidewalls, and the location and structure of concentric bends in the cylinders is determined by the shape of the trenches. The innate etching contrast, the spontaneous sharp bends and junctions, and the range of demonstrated periodicity and line/space ratios make these conformationally asymmetric rod-coil polymers attractive for nanoscale pattern generation.

Fluorescent polymer cubosomes and hexosomes with aggregation-induced emission

Fluorescent polymer cubosomes and hexosomes with aggregation-induced emission (AIE) were prepared from amphiphilic block copolymers PEG-b-PTPEMA where the hydrophobic block PTPEMA was a polymethacrylate with tetraphenylethene (TPE) as the AIE side group. Four highly asymmetric block copolymers with hydrophilic block weight ratio f PEG ≤ 20% were synthesized. Cubosomes and hexosomes with strong fluorescence emission were obtained by nanoprecipitation of polymers with f PEG < 9% in dioxane/water and THF/water systems. Their ordered internal structures were studied by electron microscopy (cryo-EM, SEM and TEM) and the X-ray scattering technique (SAXS). To elucidate the formation mechanisms of these inverted colloids, other parameters influencing the morphologies, like the water content during self-assembly and the organic solvent composition, were also investigated. This study not only inspires people to design novel building blocks for the preparation of functional cubosomes and hexosomes, but also presents the first AIE fluorescent polymer cubosome and hexosome with potential applications in bio-related fields.

Tailored Polymer Particles with Ordered Network Structures in Emulsion Droplets

The structural control of block copolymer (BCP) particles, which determines their properties and utilities, is quite important. Understanding the structural relationship between solution-cast samples and polymer particles in a confined space is necessary to precisely regulate the internal structure of polymer particles. Therefore, a facile method by choosing an appropriate selective solvent is reported to prepare spherical polymer particles with ordered network structures. The rod-coil BCP, poly(dimethylsiloxane)-b-poly{2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene} (PDMS-b-PMPCS), was chosen as a model polymer because of its strong phase segregation ability. First, the structures of the BCP with a thermodynamically stable lamellar structure cast from different selective solvents were systematically studied. Then, a polymer particle with the same internal structure as that of the solution-cast sample can be easily prepared by self-assembling in an emulsion confined space. The relatively large particle size is of importance in this process because the large value of the particle size to periodicity ratio can provide a weak confined environment. This method helps us understand the inherent self-assembling mechanism of polymer particles in an emulsion confined space and accurately control the internal structure of the polymer particle obtained.

Photo-crosslinked polymer cubosomes as a recyclable nanoreactor in organic solvents

Photo-crosslinked polymer cubosomes can work as robust nanoreactor under organic solvent condition without structural degradation.

Polymer Cubosomes: Infinite Cubic Mazes and Possibilities

Block copolymers (BCPs) have been indispensable building blocks to create a range of soft nanostructures including discrete particulates (micelles and vesicles) and periodic structures via spontaneous assembly in bulk and in solution. The size, shape, and phase of these structures can be controlled by the rational design of the molecular structure of building blocks based on the structural analogy of BCPs to lipids and small molecule surfactants. Inverse bicontinuous cubic mesophases of polymers, or polymer cubosomes when in colloidal forms, are emerging nanostructures composed of triply periodic minimal surfaces (TPMSs) of block copolymer bilayers. Created by spontaneous assembly of BCPs in solution, polymer cubosomes internalize two nonintersecting nanochannel networks arranged in a cubic crystalline order. As well-defined porous particles with highly ordered internal structures and high surface-area-to-volume ratios, polymer cubosomes can be used for chemical reactors or bioreactors, carriers capable of cargo loading and release, and scaffolds for nanotemplating. However, despite their structural similarity to lipid cubosomes and applicability, polymer cubosomes have been only sporadically observed as an outcome of serendipity until recent studies demonstrated that BCPs could form well-defined polymer cubosomes in solution.In this Account, we describe our recent progress in creating polymer cubic mesophases and their colloidal particles (polymer cubosomes) in dilute solution. BCPs with nonlinear architectures (dendritic-linear, branched-linear, and branched-branched BCPs) preferentially self-assembled to inverse mesophases in solution when the block ratio (f), defined as a molecular weight ratio of the hydrophilic block to that of the hydrophobic block, was small (<10%). The resulting lyotropic structures transformed from flat bilayers to cubic phases of primitive cubic and double diamond lattices and finally to inverted hexagonal phases as f decreased. We proposed that the architecture of a BCP plays an important role in the preferential formation of polymer cubosomes in solution. The presence of the bulky hydrophilic block limited chain stretching of the hydrophobic polymer block, which would increase the packing parameter of the BCP to greater than unity, a prerequisite for inverse mesophase formation. The structural characteristics of polymer cubosomes, such as lattice symmetries, pore sizes, and lattice parameters, could also be controlled by fine-tuning the structural parameters of BCPs. We also suggested nonsynthetic methods to precisely control the phase and internal lattice of inverse mesophases of BCPs by the coassembly of two BCPs with different block ratios (mix-and-match approach) and the modulation of the affinity of the common solvent toward the hydrophobic block of the BCP. To investigate the potential applications of polymer cubosomes, we prepared inorganic photonic crystals using a cubosome-templated synthesis. We also discussed the utilization of cubosomes as chemical reactors by functionalization of the surface and the covalent stabilization of transient self-assembled structures via cross-linking of the hydrophobic domain. This Account reflects the efforts of synthetic chemists to understand the self-assembly behavior of BCPs to form complex morphologies in solution. We hope that our Account inspires efforts from chemists and other scientists to further understand these structures with infinite mazes of complexity and possibility.

Bicontinuous cubic phases in biological and artificial self-assembled systems

Nature has created innumerable life forms with miraculous hierarchical structures and morphologies that are optimized for different life events through evolution over billions of years. Bicontinuous cubic structures, which are often described by triply periodic minimal surfaces (TPMSs) and their constant mean curvature (CMC)/parallel surface companions, are of special interest to various research fields because of their complex form with unique physical functionalities. This has prompted the scientific community to fully understand the formation, structure, and properties of these materials. In this review, we summarize and discuss the formation mechanism and relationships of the relevant biological structures and the artificial self-assembly systems. These structures can be formed through biological processes with amazing regulation across a great length scales; nevertheless, artificial construction normally produces the structure corresponding to the molecular size and shape. Notably, the block copolymeric system is considered to be an applicable and attractive model system for the study of biological systems due to their versatile design and rich phase behavior. Some of the phenomena found in these two systems are compared and discussed, and this information may provide new ideas for a comprehensive understanding of the relationship between molecular shape and resulting interface curvature and the self-assembly process in living organisms. We argue that the co-polymeric system may serve as a model to understand these biological systems and could encourage additional studies of artificial self-assembly and the creation of new functional materials.

Self-assembly of Organic Nanomaterials and Biomaterials: The Bottom-Up Approach for Functional Nanostructures Formation and Advanced Applications

In this paper, we survey recent advances in the self-assembly processes of novel functional platforms for nanomaterials and biomaterials applications. We provide an organized overview, by analyzing the main factors that influence the formation of organic nanostructured systems, while putting into evidence the main challenges, limitations and emerging approaches in the various fields of nanotechology and biotechnology. We outline how the building blocks properties, the mutual and cooperative interactions, as well as the initial spatial configuration (and environment conditions) play a fundamental role in the construction of efficient nanostructured materials with desired functional properties. The insertion of functional endgroups (such as polymers, peptides or DNA) within the nanostructured units has enormously increased the complexity of morphologies and functions that can be designed in the fabrication of bio-inspired materials capable of mimicking biological activity. However, unwanted or uncontrollable effects originating from unexpected thermodynamic perturbations or complex cooperative interactions interfere at the molecular level with the designed assembly process. Correction and harmonization of unwanted processes is one of the major challenges of the next decades and requires a deeper knowledge and understanding of the key factors that drive the formation of nanomaterials. Self-assembly of nanomaterials still remains a central topic of current research located at the interface between material science and engineering, biotechnology and nanomedicine, and it will continue to stimulate the renewed interest of biologist, physicists and materials engineers by combining the principles of molecular self-assembly with the concept of supramolecular chemistry.

Self-assembly of block copolymers towards mesoporous materials for energy storage and conversion systems

This paper reviews the progress in the field of block copolymer-templated mesoporous materials, including synthetic methods, morphological and pore size control and their potential applications in energy storage and conversion devices.

Core-Shell and Zigzag Nanostructures from a Thin Film Silicon-Containing Conformationally Asymmetric Triblock Terpolymer

The self-assembly of multiblock copolymers generates diverse hierarchical nanostructures and greatly extends the range of microdomain geometries beyond those produced by diblock copolymers. We report the synthesis of a conformationally asymmetric ABC triblock terpolymer in which the end blocks are a mesogen-jacketed liquid crystalline polymer and poly(dimethylsiloxane), respectively, and its self-assembly under mixed solvent vapor annealing forms a range of sphere, cylinder, and perforated lamellar core-shell morphologies, as well as stacked multilevel structures. Sub-7 nm diameter SiO_x nanopatterns were generated by selective plasma etching of the small volume fraction Si-containing core block giving a line/space ratio of ∼1:4. Moreover, the conformational asymmetry of this terpolymer leads to zigzag cylinders on a flat substrate and stable cylinder alignment transverse to template sidewalls within lithographically patterned trenches.

Block copolymer microparticles comprising inverse bicontinuous phases prepared via polymerization-induced self-assembly

Traditionally, post-polymerization processing routes have been used to obtain a wide range of block copolymer morphologies. However, this self-assembly approach is normally performed at rather low copolymer concentration, which precludes many potential applications. Herein, we report a facile method for the preparation of block copolymer particles exhibiting complex internal morphology via polymerization-induced self-assembly (PISA). More specifically, a series of diblock copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) alternating copolymerization of styrene (St) with N-phenylmaleimide (NMI) using a poly(N,N-dimethylacrylamide) (PDMAC) stabilizer as a soluble precursor. Conducting such PISA syntheses in a 50 : 50 w/w ethanol/methyl ethyl ketone (MEK) mixture leads directly to the formation of micrometer-sized PDMAC-P(St-alt-NMI) diblock copolymer particles at 20% w/w solids. Adjusting the degree of polymerization (DP) of the core-forming P(St-alt-NMI) block to target highly asymmetric copolymer compositions provides convenient access to an inverse bicontinuous phase. TEM studies of intermediate structures provide useful insights regarding the mechanism of formation of this phase. SEM studies indicate that the final copolymer particles comprise perforated surface layers and possess nanostructured interiors. In addition, control experiments using 1,4-dioxane suggest that the high chain mobility conferred by the MEK co-solvent is essential for the formation of such inverse bicontinuous structures. One-pot PISA formulations are reproducible and involve only cheap, commercially available starting materials, so they should be readily amenable to scale-up. This augurs well for the potential use of such nanostructured micrometer-sized particles as new organic opacifiers for paints and coatings.

Scalable preparation of alternating block copolymer particles with inverse bicontinuous mesophases

Block copolymer particles with controlled morphologies are of great significance in nanomaterials and nanotechnology. However, ordered inverse morphologies are difficult to achieve due to complex mechanism and formation conditions. Here we report scalable preparation of amphiphilic alternating block copolymer particles with inverse bicontinuous mesophases via polymerization-induced self-assembly (PISA). Concentrated dispersion copolymerizations (up to 40% solid content) of styrene (St) and pentafluorostyrene (PFS) employing a short poly(N,N-dimethylacrylamide) (PDMA29) stabilizer block lead to the formation of well-defined, highly asymmetric PDMA29-b-P(St-alt-PFS)x block copolymers with precise compositions and various morphologies, from simple spheres to ordered inverse cubosome mesophases. The particle morphology is affected by the molecular weight, solid content, and nature of the cosolvents. The cubosome structure is confirmed by electron microscopies and small angle X-ray scattering spectroscopy. This scalable PISA approach offers facile access to ordered inverse mesophases, significantly expanding the PISA morphology scope and enabling its applicability to the materials science fields.

Effect of the molecular weight distribution of the hydrophobic block on the formation of inverse cubic mesophases of block copolymers with a discrete branched hydrophilic block

The molecular weight distribution of the hydrophobic block of block copolymers directly influences their self-assembled structures in solution.

Temperature-controlled formation of inverse mesophases assembled from a rod–coil block copolymer

Temperature was adjusted to control the formation of inverse mesophases which can be used as templates to prepare inorganic materials.