Self-Assembled Smectic Phases in Rod-Coil Block Copolymers

Ion transport in helical-helical polypeptide polymerized ionic liquid block copolymers

Helical-helical polypeptide polymerized ionic liquid block copolymers (PPIL BCPs) are synthesized to investigate the role of helical structure on self-assembly and ionic conductivity. PPIL BCPs, consisting of a cationic polypeptide (PTPLG) with bis(trifluoromethane sulfonimide) (TFSI) counterion and varying lengths connected to a length-fixed neutral poly-(γ-benzyl-L-glutamate) (PBLG) block, exhibit stable helical conformations with minimal glass transition (Tg) variation. Here, we show that increasing PIL composition leads to a transition from poorly ordered to highly ordered lamellar (LAM) structures with the highest PIL content BCP forming a bilayer LAM structure with close-packed helices. This morphology yields a 1.5 order of magnitude higher Tg- and volume fraction-normalized ionic conductivity and a morphology factor f > 0.8 compared to less ordered BCPs with f < 0.05 and f = 2/3 for ideal lamellae. These results highlight the critical role of helical structure in optimizing ion transport, offering a design strategy for high-performance solid electrolytes.

Statistical and Block Copolymers of n-Dodecyl and Allyl Isocyanate via Titanium-Mediated Coordination Polymerization: A Route to Polyisocyanates with Improved Thermal Stability

Well-defined amorphous/semi-crystalline statistical copolymers of n-dodecyl isocyanate, DDIC, and allyl isocyanate, ALIC, were synthesized via coordination polymerization using the chiral half-titanocene complex CpTiCl2(O-(S)-2-Bu) as an initiator. In the frame of the terminal model, the monomer reactivity ratios of the statistical copolymers were calculated using both well-known linear graphical methods and the computer program COPOINT. The molecular and structural characteristics of the copolymers were also calculated. The thermal properties of these samples were studied by differential scanning calorimetry, DSC, measurements. The kinetics of the thermal decomposition of the statistical copolymers was studied by thermogravimetric analysis, TGA, and differential thermogravimetry, DTG, and the activation energy of this process was calculated by employing several theoretical models. Moreover, block copolymers with the structure P[DDIC-b-(DDIC-co-ALIC)] were synthesized by sequential addition of monomers and coordination polymerization methodologies. The samples were characterized by nuclear magnetic resonance, NMR, spectroscopy; size exclusion chromatography, SEC; and DSC. The thermal stability of the blocks was also studied by TGA and DTG and compared to the corresponding statistical copolymers, showing that the macromolecular architecture greatly affects the properties of the copolymers. A thiol-ene click post-polymerization reaction was performed to introduce aromatic groups along the polyisocyanate chain in order to improve the thermal stability of the parent polymers. Evidently, these statistical and block copolymers can be employed as precursors for the synthesis of novel polyisocyanate-based materials.

Cross-domain Chirality Transfer in Self-Assembly of Chiral Block Copolymers

Chirality transfer is essential to acquire helical hierarchical superstructures from the self-assembly of supramolecular materials. By taking advantage of chirality transfers at different length scales through intra-chain and inter-chain chiral interactions, helical phase (H*) can be formed from the self-assembly of chiral block copolymers (BCPs*). In this study, chiral triblock terpolymers, polystyrene-b-poly(ethylene oxide)-b-poly(L-lactide) (PS-PEO-PLLA), and polystyrene-b-poly(4-vinylpyridine)-b-poly(L-lactide) (PS-P4VP-PLLA) are synthesized for self-assembly. For PS-PEO-PLLA with an achiral PEO mid-block that is compatible with PLLA (chiral end-block), H* can be formed while the block length is below a critical value. By contrast, for the one with achiral P4VP mid-block that is incompatible with PLLA, the formation of H* phase would be suppressed regardless of the length of the mid-block, giving cylinder phase. Those results elucidate a new type of chirality transfer across the phase domain that is referred as cross-domain chirality transfer, providing complementary understanding of the chirality transfer at the interface of phase-separated domains.

Morphologies of Surface Perforations and Parallel Cylinders Coexisting in Terraced Films of Block Copolymer/Homopolymer Blends with Oxygen Plasma Etching

This study has demonstrated how oxygen plasma etching carves surface structures for thin films of polystyrene-block-poly(methyl methacrylate)/homopolystyrene blends. By tuning the weight-fraction ratio, blend films form perforations and cylinders on the SiOx/Si substrate. Since perforations exist only on the free surface and substrate interface, short exposure to oxygen plasma to quickly etch the PMMA component produces distorted hexagonal arrays of nanodots on the free surface. The interior of the blend films forms polygrain micro-structures composed of parallel cylinders with an in-plane random orientation. Oxygen plasma etching imposed on the fractured surfaces results in five morphologies: (i) distorted hexagonal arrays of nanoholes, (ii) layer-by-layer stacks, (iii) zigzag-like arrays, (iv) intertwined rectangular arrays of nanodots and nanoholes, and (v) intertwined parallelogram arrays of nanodots and nanoholes. The morphologies suggest synergic effects of grain orientations, stresses, spatial confinement, local segregation of chains, and etching kinetics on the terraced films with oxygen plasma etching.

Synthesis and Characterization of Statistical and Block Copolymers of n-Hexyl Isocyanate and 3-(Triethoxysilyl) Propyl Isocyanate via Coordination Polymerization

Well-defined statistical copolymers of n-hexyl isocyanate, HIC, and 3-(triethoxysilyl)propyl isocyanate, TESPI, were synthesized via coordination polymerization mechanism, employing a chiral half-titanocene complex as initiator. The monomer reactivity ratios of the statistical copolymers were calculated using linear graphical methods and the computer program COPOINT in the frame of the terminal model. The molecular and structural characteristics of the copolymers were also calculated. The kinetics of the thermal decomposition of the statistical copolymers was studied by Thermogravimetric Analysis, TGA, and Differential Thermogravimetry, DTG, and the activation energy of this process was calculated employing several theoretical models. In addition, block copolymers constituted from PHIC and PTESPI blocks were synthesized by sequential coordination polymerization. All samples were characterized by nuclear magnetic resonance, NMR, spectroscopy and size exclusion chromatography, SEC. The thermal stability of the blocks was also studied by TGA and DTG and compared to the corresponding statistical copolymers.

Confined Self-Assemblies of Chiral Block Copolymers in Thin Films

Self-assembly of chiral block copolymers (BCPs*) can give rise to ordered chiral nanostructures, that is, a helical phase (H* phase), via chirality transfer from the molecular level to mesoscale. In the present work, we reported the self-assembly of BCPs* under one-dimensional spatial confinement. The morphological dependence of self-assembled BCPs* on the molecular weights and the film thickness was investigated. As chiral nanostructures, the H* phase can be formed in bulk, nonchiral nanostructures that were observed in the thin films. Also, the topology effect of self-assembly of BCPs* was examined. The self-assembly of BCPs* with a star-shaped topology exhibited a distinct morphology compared with that of linear BCPs*. The present work provides new insight into the chirality transfer of macromolecules under spatial confinement.

Microphase separation in helix-coil block copolymer melts: computer simulation

By means of molecular dynamics simulation, the process of the microphase separation in the melts of diblock helix-coil copolymers comprising a flexible and a helical block was studied. The resulting microstructures were examined, and the spatial distribution of the blocks and molecular packing were investigated. The phase diagram was built in terms of the fraction of the helical block and the incompatibility parameter of the blocks. The comparison of the diagrams for helix-coil and the classic coil-coil copolymer blends was carried out. It was shown that the total region where the ordering into distinctive microstructures takes place is similar for both diagrams. But for the helix-coil copolymers the area of the cylinders splits into the region of those with circular and elliptical cross-sections; the bicontinuous phase area is much wider; in the lamellar phases, the helical blocks were oriented precisely perpendicular to the lamellar interface, forming a cohesive interlocked structure of densely packed helices.

100th Anniversary of Macromolecular Science Viewpoint: Opportunities for Liquid Crystal Polymers in Nanopatterning and Beyond

Liquid-crystal polymers (LCPs) integrate at a molecular level the characteristics of two important material classes, i.e., liquid crystals (LCs) and polymers. As a result, they exhibit a wide variety of intriguing physical phenomena and have useful properties in various settings. In the nearly 50 years since the discovery of the first melt-processable LCPs, there has been a remarkable expansion in the field encompassing the development of new chain architectures, the incorporation of new classes of mesogens, and the exploration of new properties and applications. As engineering materials, LCPs are historically best known in the context of high strength fibers. In a more contemporary study, the pairing of LC mesophase assembly with block copolymer (BCP) self-assembly in LC BCPs has resulted in a fascinating interplay of ordering phenomena and rich phase behavior, while lightly cross-linked networks, LC elastomers, are extensively investigated as shape memory materials based on their thermomechanical actuation. As this Viewpoint describes, these and other examples are active areas of research in which new, compelling opportunities for LCPs are emerging. We highlight a few selected areas that we view as being potentially significant in the near future, with a particular emphasis on nanopatterning. Here, the ability to readily access small feature sizes, the fluidity of the LC mesophase, and LC-based handles for achieving orientation control present a compelling combination. Opportunities for LCPs are also presented under the broad rubric of "beyond nanopatterning", and we discuss relevant challenges and potential new directions in the field.

Modulating the Molecular Geometry and Solution Self-Assembly of Amphiphilic Polypeptoid Block Copolymers by Side Chain Branching Pattern

Solution self-assembly of coil-crystalline diblock copolypeptoids has attracted increasing attention due to its capability to form hierarchical nanostructures with tailorable morphologies and functionalities. While the N-substituent (or side chain) structures are known to affect the crystallization of polypeptoids, their roles in dictating the hierarchical solution self-assembly of diblock copolypeptoids are not fully understood. Herein, we designed and synthesized two types of diblock copolypeptoids, i.e., poly(N-methylglycine)-b-poly(N-octylglycine) (PNMG-b-PNOG) and poly(N-methylglycine)-b-poly(N-2-ethyl-1-hexylglycine) (PNMG-b-PNEHG), to investigate the influence of N-substituent structure on the crystalline packing and hierarchical self-assembly of diblock copolypeptoids in methanol. With a linear aliphatic N-substituent, the PNOG blocks pack into a highly ordered crystalline structure with a board-like molecular geometry, resulting in the self-assembly of PNMG-b-PNOG molecules into a hierarchical microflower morphology composed of radially arranged nanoribbon subunits. By contrast, the PNEHG blocks bearing bulky branched aliphatic N-substituents are rod-like and prefer to stack into a columnar hexagonal liquid crystalline mesophase, which drives PNMG-b-PNEHG molecules to self-assemble into symmetrical hexagonal nanosheets in solution. A combination of time-dependent small/wide-angle X-ray scattering and microscopic imaging analysis further revealed the self-assembly mechanisms for the formation of these microflowers and hexagonal nanosheets. These results highlight the significant impact of the N-substituent architecture (i.e., linear versus branched) on the supramolecular self-assembly of diblock copolypeptoids in solution, which can serve as an effective strategy to tune the geometry and hierarchical structure of polypeptoid-based nanomaterials.

The Sequence of a Step-Growth Copolymer Can Be Influenced by Its Own Persistence Length

Synthetic copolymer sequences remain challenging to control, and there are features of even simple one-pot, solution-based copolymerizations that are not yet fully understood. In previous simulations on step-growth copolymerizations in solution, we demonstrated that modest variations in the attractions between type A and B monomers could significantly influence copolymer sequence through an emergent aggregation and phase separation initiated by the lengthening of nascent oligomers. Here we investigate how one aspect of a copolymer's geometry-its flexibility-can modulate those effects. Our simulations show the onset of strand alignment within the polymerization-induced aggregates as chain stiffness increases and demonstrate that this alignment can influence the resulting copolymer sequences. For less flexible copolymers, with persistence lengths ≥10 monomers, modest nonbonded attractions of ∼k_BT between monomers of the same type yield A and B blocks of a characteristic length and result in a polydispersity index that grows rapidly, peaks, and then diminishes as the reaction proceeds. These results demonstrate that for copolymer systems with modest variations in intermonomer attractions and physically realistic flexibilities a nascent copolymer's persistence length can influence its own sequence.

Mono- and bilayer smectic liquid crystal ordering in dense solutions of "gapped" DNA duplexes

Although its mesomorphic properties have been studied for many years, only recently has the molecule of life begun to reveal the true range of its rich liquid crystalline behavior. End-to-end interactions between concentrated, ultrashort DNA duplexes-driving the self-assembly of aggregates that organize into liquid crystal phases-and the incorporation of flexible single-stranded "gaps" in otherwise fully paired duplexes-producing clear evidence of an elementary lamellar (smectic-A) phase in DNA solutions-are two exciting developments that have opened avenues for discovery. Here, we report on a wider investigation of the nature and temperature dependence of smectic ordering in concentrated solutions of various "gapped" DNA (GDNA) constructs. We examine symmetric GDNA constructs consisting of two 48-base pair duplex segments bridged by a single-stranded sequence of 2 to 20 thymine bases. Two distinct smectic layer structures are observed for DNA concentration in the range [Formula: see text] mg/mL. One exhibits an interlayer periodicity comparable with two-duplex lengths ("bilayer" structure), and the other has a period similar to a single-duplex length ("monolayer" structure). The bilayer structure is observed for gap length ≳10 bases and melts into the cholesteric phase at a temperature between 30 °C and 35 °C. The monolayer structure predominates for gap length ≲10 bases and persists to [Formula: see text]C. We discuss models for the two layer structures and mechanisms for their stability. We also report results for asymmetric gapped constructs and for constructs with terminal overhangs, which further support the model layer structures.

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.

Direct synthesis of light-emitting triblock copolymers from RAFT polymerization

We introduce a straightforward and clean method to synthesize semiconducting triblockcopolymers (tri-BCPs) using RAFT polymerization.

Synthesis and Self-Assembly of Conjugated Block Copolymers

In the past two decades, conjugated polymers (CPs) have drawn great attention due to their excellent conductivity and charge mobility, rendering them broad applications in organic electronics. Controlling over the morphologies and nanostructures of CPs is very important to improve the performance of CP-based devices, which is still a tremendously difficult task. Conjugated block copolymers (cBCPs), composed of different CP blocks or CP coupled with coiled polymeric blocks, not only maintain the advantages of high conductivity and mobility but also demonstrate features of morphological versatility and tunability. Due to the strong π-π interaction and crystallinity of the conjugated backbones, the self-assembly behaviors of cBCPs are very complicated and largely remain to be explored. In this tutorial review, we first summarize the general synthetic methods for different types of cBCPs. Then, recent studies on the self-assembly behaviors of cBCPs are discussed, with an emphasis on the structural factors that affect the morphologies of cBCPs both in bulk and thin film states. Finally, we briefly provide our outlook on the future research of the self-assembly of cBCPs.

DNA Self-Assembly Mediated by Programmable Soft-Patchy Interactions

Adding shape and interaction anisotropy to a colloidal particle offers exquisitely tunable routes to engineer a rich assortment of complex-architected structures. Inspired by the hierarchical self-assembly concept with block copolymers and DNA liquid crystals and exploiting the unique assembly properties of DNA, we report here the construction and self-assembly of DNA-based soft-patchy anisotropic particles with a high degree of modularity in the system's design. By programmable positioning of thermoresponsive polymeric patches on the backbone of a stiff DNA duplex with linear and star-shaped architecture, we reversibly drive the DNA from a disordered ensemble to a diverse array of long-range ordered multidimensional nanostructures with tunable lattice spacing, ranging from lamellar to bicontinuous double-gyroid and double-diamond cubic morphologies, through the alteration of temperature. Our results demonstrate that the proposed hierarchical self-assembly strategy can be applied to any kind of DNA nanoarchitecture, highlighting the design principles for integration of self-assembly concepts from the physics of liquid crystals, block copolymers, and patchy colloids into the continuously growing interdisciplinary research field of structural DNA nanotechnology.

Spiral Hierarchical Superstructures from Twisted Ribbons of Self-Assembled Chiral Block Copolymers

Spiral hierarchical superstructures were found in the self-assembly of chiral block copolymers (BCPs*) composed of a chiral poly(l-lactide) (PLLA) and an achiral polystyrene (PS) as major and minor blocks, respectively. The PLLA helical chain with semiflexible rod-like character as compared to the random coil of PS results in self-assembly with a conformational asymmetry effect overwhelming the compositional one. Consequently, instead of the forming PS cylinder microdomains in the PLLA matrix, a smectic liquid-crystal-like bilayer sandwiched with PLLA and PS microdomains will be formed. Owing to twisting and bending due to the chiral cholesteric liquid-crystal-like force field combined with steric hindrance at the chiral interface, the forming bilayers (twisted ribbon) will develop into either a concentric lamellar texture from scrolling or roll-cake textures from spiraling. This study might bring a concept for the formation of spiral hierarchical superstructures from self-assembled bilayers for device application.

Single chain in mean field simulation of flexible and semiflexible polymers: comparison with discrete chain self-consistent field theory

Single chain in mean field (SCMF) simulation is a theoretical framework performing Monte Carlo moves of explicit polymer chains under quasi-instantaneously updated external fields which were originally imported from the self-consistent field theory (SCFT). Even though functional-based hybrid simulations are often used to compare the results of SCFT and MC simulation, the adoption of a finite number of coarse-grained segments makes direct comparison rather difficult. In this study, we perform SCMF simulation of block copolymers using various chain models and quantitatively compare it with discrete chain SCFT (DCSCFT) which finds the mean field solution of polymers with a finite number of segments. By comparing free energy and natural period of the symmetric block copolymer lamellar phase, we systematically show that DCSCFT serves as an intermediate step between SCMF simulation and SCFT. In addition, by adopting angle dependent bond potential, we perform SCMF simulation of semiflexible polymers using bead-spring and freely jointed chain models. As the chain stiffness increases, the lamellar phase tends to align perpendicular to the surfaces when confined between two neutral walls. We also investigate the effects of fluctuation and chain stiffness on the distribution of chain ends. The tendency of chain end segregation towards the surfaces turns out to increase as the chain stiffness increases for both homopolymer and block copolymer systems.

Liquid Crystal Ordering in the Hexagonal Phase of Rod-Coil Diblock Copolymers

Density functional theory of rod-coil diblock copolymers, developed recently by the authors, has been generalised and used to study the liquid crystal ordering and microphase separation effects in the hexagonal, lamellar and nematic phases. The translational order parameters of rod and coil monomers and the orientational order parameters of rod-like fragments of the copolymer chains have been determined numerically by direct minimization of the free energy. The phase diagram has been derived containing the isotropic, the lamellar and the hexagonal phases which is consistent with typical experimental data. The order parameter profiles as functions of temperature and the copolymer composition have also been determined in different anisotropic phases. Finally, the spatial distributions of the density of rigid rod fragments and of the corresponding orientational order parameter in the hexagonal phase have been calculated.

Vertical Lamellae Formed by Two-Step Annealing of a Rod-Coil Liquid Crystalline Block Copolymer Thin Film

Silicon-containing block copolymer thin films with high interaction parameter and etch contrast are ideal candidates to generate robust nanotemplates for advanced nanofabrication, but they typically form in-plane oriented microdomains as a result of the dissimilar surface energies of the blocks. Here, we describe a two-step annealing method to produce vertically aligned lamellar structures in thin film of a silicon-containing rod-coil thermotropic liquid crystalline block copolymer. The rod-coil block copolymer with the volume fraction of the Si-containing block of 0.22 presents an asymmetrical lamellar structure in which the rod block forms a hexatic columnar nematic liquid crystalline phase. A solvent vapor annealing step first produces well-ordered in-plane cylinders of the Si-containing block, then a subsequent thermal annealing promotes the phase transition from in-plane cylinders to vertical lamellae. The pathways of the order-order transition were examined by microscopy and in situ using grazing incidence small-angle X-ray scattering and wide-angle X-ray scattering.

Switching between Stacked Toroids and Helical Supramolecular Polymers in Aqueous Nanotubules

Although significant advances have been made in supramolecular tubules, reversible polymerization in the tubular walls while maintaining their intact structure remains a great challenge. Here, reversible helical supramolecular polymerization of stacked toroids is reported, while maintaining tubular structures in aqueous solution. At room temperature, the tubules consist of discrete toroid stackings with hydrophobic interior. Upon heating, the tubules based on toroid stackings undergo a reversible helical supramolecular polymerization to transform into helical tubules by interconnecting between spirally open toroids. The helical polymerization arises from a tilting transition of the closed toroids that transform into spirally open toroids driven by the thermal dehydration of a hydrophilic oligoether dendron surrounding the toroid frameworks.

Unique aqueous self-assembly behavior of a thermoresponsive diblock copolymer

It is well-recognized that block copolymer self-assembly in solution typically produces spheres, worms or vesicles, with the relative volume fraction of each block dictating the copolymer morphology. Stimulus-responsive diblock copolymers that can undergo either sphere/worm or vesicle/worm transitions are also well-documented. Herein we report a new amphiphilic diblock copolymer that can form spheres, worms, vesicles or lamellae in aqueous solution. Such self-assembly behavior is unprecedented for a single diblock copolymer of fixed composition yet is achieved simply by raising the solution temperature from 1 °C (spheres) to 25 °C (worms) to 50 °C (vesicles) to 70 °C (lamellae). Heating increases the degree of hydration (and hence the effective volume fraction) of the core-forming block, with this parameter being solely responsible for driving the sphere-to-worm, worm-to-vesicle and vesicle-to-lamellae transitions. The first two transitions exhibit excellent reversibility but the vesicle-to-lamellae transition exhibits hysteresis on cooling. This new thermoresponsive diblock copolymer provides a useful model for studying such morphological transitions and is likely to be of significant interest for theoretical studies.

Metal-free anionic polymerization of n-hexyl isocyanate catalyzed by phosphazene bases

Metal-free anionic polymerization of n-hexyl isocyanate (HIC) catalyzed by phosphazene bases in THF at −98 °C under 10⁻⁶ Torr was attempted to obtain poly(n-hexyl isocyanate) (PHIC) peptide mimics with a high purity.

Synthesis and Solution Self-Assembly Properties of Cyclic Rod-Coil Diblock Copolymers

Typical cyclic diblock polymers are synthesized from their linear precursors via the ring-closure strategy in dilute conditions. Here we demonstrate a pseudo-high-dilution condition strategy for the efficient synthesis of cyclic rod-coil diblock copolymer from its linear precursor in selective solvents. The critical association concentration (CAC) of linear precursor is used for the control of unimer concentration during cyclization, while high copolymer synthetic concentrations are achieved via the dynamic equilibrium between unimers and micelles. The effects of CAC and micelle concentration on cyclization yield are studied and pure cyclic rod-coil diblock copolymer was obtained after azide resin treatment. Property investigations show the cyclic rod-coil copolymer has a larger second virial coefficient than its linear counterpart and self-assembles in selective solvents to form larger but looser spherical micelles due to its constraint topological structure.

Phase behavior of disk-coil block copolymers under cylindrical confinement: Curvature-induced structural frustrations

In this paper, we explore the self-assembly behavior of disk-coil block copolymers (BCPs) confined within a cylinder using molecular dynamics simulations. As functions of the diameter of the confining cylinder and the number of coil beads, concentric lamellar structures are obtained with a different number of alternating disk-rich and coil-rich bilayers. Our paper focuses on the curvature-induced structural behavior in the disk-rich domain of a self-assembled structure, which is investigated by calculating the local density distribution P(r) and the orientational distribution G(r,θ). In the inner layers of cylinder-confined disk-coil BCPs, both P(r) and G(r,θ) show characteristic asymmetry within a bilayer which is directly contrasted with the bulk and slab-confined disk-coil BCPs. We successfully explain the structural frustration of disks arising from the curved structure due to packing frustration of disks and asymmetric stretching of coils to the regions with different curvatures in a bilayer. Our results are important to understand the self-assembly behavior of BCPs containing a rigid motif in a confined structure, such as a self-assembled structure of bacteriochlorophyll molecules confined by a lipid layer to form a chlorosome, the photosynthetic antennae complex found in nature.

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.

Gradient copolymer micelles: an introduction to structures as well as structural transitions

Exhibiting variation of the composition along a chain, gradient copolymers bring new blood to the old story of polymeric micelles. The gradient chain structure results in some special features in micellar structures and leads to unique structural transitions, potentially leading to new properties and applications. Henceforth, gradient copolymer micellar structures and their transitions from the viewpoint of soft matter physics will be reviewed. Concepts such as a diffuse interface, shrinkage-stretching of micelles, and intrinsic temperature responsiveness are summarized from current research, which highlight new characteristic structures, relaxation modes and novel properties of micelles, respectively.

Advances toward the effective use of block copolymers as organic photovoltaic active layers

Donor/acceptor block copolymers for organic photovoltaic active layers are discussed from first principles through the modern state-of-the-art and future perspectives.

Complex Phase Behavior and Network Characteristics of Midblock-Solvated Triblock Copolymers as Physically Cross-Linked Soft Materials

In the presence of a midblock-selective solvent, triblock copolymers not only self-organize but also form a molecular network. Thermoplastic elastomer gels constitute examples of such materials and serve as sealants and adhesives, as well as ballistic, microfluidic, and electroactive media. We perform Monte Carlo and dissipative particle dynamics simulations to investigate the phase behavior and network characteristics of these materials. Of particular interest is the existence of a truncated octahedral morphology that resembles the atomic arrangement of various inorganic species. Both simulation approaches quantify the midblock bridges responsible for network development and thus provide a detailed molecular picture of these composition-tunable soft materials.

Domain swelling in ARB-type triblock copolymers via self-adjusting effective dispersity

We investigated the domain spacing of an ordered structure formed by polydisperse ARB-type triblock copolymers (triBCPs) with random middle R blocks consisting of A and B monomers. ARB-type triBCPs were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, and the dispersities of all samples were controlled as narrow as ∼1.2. From the bulk and film morphologies, it was found that the domain swelling increases as the content of middle R blocks increases, which implies that the middle R block even with a small content plays a critical role in dilating the domain spacing. Since the random middle R blocks are energetically neutral, they can be segregated into either A or B blocks. The strong stretching theory (SST) suggests that the dispersities of the resulting constituent blocks are maximized to reduce the elastic energy associated with chain stretching, thereby leading to the dilation of domain spacing.

Self-assembly of maltoheptaose-b-PMMA block copolymer systems: 10nm Resolution in thin film and bulk states

This paper describes the self-assembly of oligosaccharide-based hybrid block copolymers (BCPs) consisting of maltoheptaose (MH) and poly(methyl methacrylate) (PMMA) into 10nm scale lamellar and cylindrical phases depending on the volume fractions of MH (ϕ_MH) and the annealing process. Time resolved SAXS study of the BCP bulk samples during thermal annealing indicated that the BCPs phase separate into 10nm scale periodical structures. The solvent vapor annealing induced self-organizations of the BCP into different phases depending on ϕ_MH and the weight fraction of THF/H₂O. BCPs with relatively higher Ø_MH, MH-b-PMMA_3k (ϕ_MH=0.27) and MH-b-PMMA_5k (ϕ_MH=0.16) self-organized into lamellar phases while the BCP sample with relatively lower ϕ_MH, MH-b-PMMA_9k (ϕ_MH=0.10), self-organized into cylindrical phase by using THF/H₂O=1/4 (w/w). On the other hand, the solvent vapor annealing with larger fraction of THF, i.e. THF/H₂O=2/3 (w/w), induced cylindrical phases for MH-b-PMMA_3k and MH-b-PMMA_5k.

Liquid crystalline bilayers self-assembled from rod-coil diblock copolymers

The structure and phase behaviour of bilayer membranes self-assembled from rod-coil diblock copolymers are studied using the self-consistent field theory, focusing on the occurrence and relative stability of liquid crystalline phases induced by the geometric shape and orientational interaction of the rod-blocks. A variety of liquid crystalline bilayers, corresponding to the smectic phases in bulk systems, are predicted to occur as equilibrium phases of the system. The ordered morphologies and phase behaviour of the system are analyzed. Phase diagrams of the self-assembled bilayers are constructed. The theoretical results provide an understanding of the formation mechanisms of these intricate phases.