Rod-coil Diblock Copolymers Research Articles

Controlled synthesis and optical investigation of conjugated rod-coil diblock copolymer based on poly(3-hexylthiophene) and poly(2-(dimethylamino)ethyl methacrylate-random-1-pyrenylmethyl methacrylate-random-methacrylate spirooxazine)

Controlled synthesis and optical investigation of conjugated rod-coil diblock copolymer based on poly(3-hexylthiophene) and poly(2-(dimethylamino)ethyl methacrylate-random-1-pyrenylmethyl methacrylate-random-methacrylate spirooxazine)

Metallo-Supramolecular Rod–Coil Block Copolymer Thin Films for Stretchable Organic Field Effect Transistor Application

Herein, to decrease the synthetic burden of the rod–coil diblock copolymers, the coordination-driven self-assembly approach is utilized to readily construct a series of polystyrene (PS)-block-poly(3-hexylthiophene) (P3HT) copolymers with dynamic heteroleptic coordination bonds between the two blocks. In detail, the chain length of the PS is varied for a fixed P3HT chain length to produce block copolymers, namely, PS85–Zn–P3HT187 (P1) and PS161–Zn–P3HT187 (P2), with comparable electrical performance to that of homopolymer P3HT (P0) in the unstrained state, along with enhanced crack onset strain and much less reduced mobility under 25–100% strain. The ability to maintain the charge transport characteristics is due to the longer coil chain length and amorphous PS regions for the dissipation of strain energy. The organic field effect transistors of P2 with a longer PS segment show only a slight change in mobility from 5.48 × 10–3 to 1.40 × 10–3 cm2 V–1 s–1 under 25–100% and maintain this mobility even after being subjected to 100 repeated stretching/releasing cycles at 50% strain. This proof-of-concept demonstration of the proposed molecular engineering approach based on the metallo-supramolecular method provides a suitable route to the molecular design of stretchable polymer semiconductors with balanced mechanical and electrical behaviors.

Tilt Modulus of Bilayer Membranes Self-Assembled from Rod-Coil Diblock Copolymers.

Quantitatively understanding membrane fission and fusion requires a mathematical model taking their underlying elastic degrees of freedom, such as the molecule's tilt, into account. Hamm-Kozlov's model is such a framework that includes a tilt modulus along with the bending modulus and Gaussian modulus. This paper investigates the tilt modulus of liquid-crystalline bilayer membranes by applying self-consistent field theory. Unlike the widely used method in molecular dynamics simulation which extracts the tilt modulus by simulating bilayer buckles with various single modes, we introduce a tilt constrain term in the free energy to stabilize bilayers with various tilt angles. Fitting the energy curve as a function of the tilt angle to Hamm-Kozlov's elastic energy allows us to extract the tilt modulus directly. Based on this novel scheme and focused on the bilayers self-assembled from rod-coil diblock copolymers, we carry out a systematic study of the dependence of the tensionless A-phase bilayer's tilt modulus on the microscopic parameters.

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/SiOx binary composites by plasma etching and reveals the core-shell morphology of the triblock terpolymer.

Liquid-Crystal Ordering and Microphase Separation in the Lamellar Phase of Rod-Coil-Rod Triblock Copolymers. Molecular Theory and Computer Simulations.

A molecular model of the orientationally ordered lamellar phase exhibited by asymmetric rod-coil-rod triblock copolymers has been developed using the density-functional approach and generalizing the molecular-statistical theory of rod-coil diblock copolymers. An approximate expression for the free energy of the lamellar phase has been obtained in terms of the direct correlation functions of the system, the Flory-Huggins parameter and the Maier-Saupe orientational interaction potential between rods. A detailed derivation of several rod-rod and rod-coil density-density correlation functions required to evaluate the free energy is presented. The orientational and translational order parameters of rod and coil segments depending on the temperature and triblock asymmetry have been calculated numerically by direct minimization of the free energy. Different structure and ordering of the lamellar phase at high and low values of the triblock asymmetry is revealed and analyzed in detail. Asymmetric rod-coil-rod triblock copolymers have been simulated using the method of dissipative particle dynamics in the broad range of the Flory-Huggins parameter and for several values of the triblock asymmetry. It has been found that the lamellar phase appears to be the most stable one at strong segregation. The density distribution of the coil segments and the segments of the two different rods have been determined for different values of the segregation strength. The simulations confirm the existence of a weakly ordered lamellar phase predicted by the density-functional theory, in which the short rods separate from the long ones and are characterized by weak positional ordering.

Crosslinking Modulated Hierarchical Self-Assembly of Rod–Coil Diblock Copolymer Patchy Nanoparticles

Crosslinking Modulated Hierarchical Self-Assembly of Rod–Coil Diblock Copolymer Patchy Nanoparticles

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.

Self-assembly of rod-coil diblock copolymer-nanoparticle composites in thin films: dissipative particle dynamics.

In this study, the assembled structures of rod-coil diblock copolymer and nanoparticle blends were studied via dissipative particle dynamics (DPD). Thin films were composed of soft confinement DPD fluid beads and the fluctuating film structure was maintained during the simulation process. Analysis of the position of nanoparticles was done in the smectic lamellar phase of the rod-coil polymer matrix, and density distributions of rods, coils, and nanoparticles were obtained as functions of the size of the nanoparticle and the DPD repulsion constant between the rod and the nanoparticle. The distribution of nanoparticles was explained by using the concept of translational entropy of nanoparticles, stretching energy of the polymer chain, relative repulsion enthalpy of nanoparticles to rods or coils, and the effect of the liquid crystalline rod.

Secondary Structures of Polypeptide-Based Diblock Copolymers Influence the Microphase Separation of Templates for the Fabrication of Microporous Carbons

In this study, we synthesized two forms of the polypeptide-based rod–coil diblock copolymer poly(ethylene oxide-b-γ-benzyl-l-glutamate) (PEO-b-PBLG), comprising hydrophilic PEO as the coil segment ...

Density Functional Approach to the Molecular Theory of Rod-Coil Diblock Copolymers

The general density functional approach is used to develop a molecular-statistical theory of rod-coil diblock copolymers which is valid in the case of both weak and strong segregation. The free energy of the rod-coil copolymer is expressed as a functional of the number densities of rod and coil monomers which depend on the translational and orientational degrees of freedom. The equilibrium densities are determined by minimization of the free energy functional and depend on the orientational and translational order parameters of the monomers. The order parameters are calculated numerically by minimization of the free energy taking into account the incompressibility condition within the formalism of Lagrange multipliers. Phase diagrams are obtained and the profiles of orientational and translational order parameters are presented as functions of temperature and the fraction of coil fragments. It is shown that the lamellar phase possesses strong orientational order and the stability of the phase is increasing with the increasing fraction of rod monomers.

Tilted Lamellar Phase of the Rod–Coil Diblock Copolymer: Dissipative Particle Dynamics Simulation

The tilted lamellar phase of a symmetric rod–coil diblock copolymer is studied by dissipative particle dynamics simulation over a wide range of degrees of block segregation. The microphase separation in the copolymer and the orientational ordering of rigid blocks in the tilted phase are investigated. For the first time, spatial profiles of the orientational order parameter and the density of monomer units of rigid and flexible blocks at various values of χN are calculated and the influence of this parameter on the value of the tilt angle is studied.

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.

Molecular theory of the tilting transition and computer simulations of the tilted lamellar phase of rod-coil diblock copolymers.

Symmetric rod-coil diblock copolymers have been simulated using the method of dissipative particle dynamics in the broad range of the Flory-Huggins parameter. It has been found that the tilted lamellar phase appears to be the most stable one at strong segregation. The rod-coil copolymer tilt angle and orientational order parameters have been determined as functions of the segregation strength. The density functional theory of rod-coil diblock copolymers has been generalized to the case of the tilted lamellar phase and used to study the stability of the orthogonal lamellar phase with respect to tilt. The orthogonal phase indeed appears to be unstable in the broad region of the parameter space in the case of relatively strong segregation. It has also been shown that the transition into the tilted lamellar phase is determined by a strong coupling between two independent tilt order parameters.

A Facile and Highly Efficient Route to Amphiphilic Star-Like Rod-Coil Block Copolymer via a Combination of Atom Transfer Radical Polymerization with Thiol-Ene Click Chemistry.

With a combination of atom transfer radical polymerization (ATRP), quasi-living Grignard metathesis method, and thiol-ene click reaction, an amphiphilic star-like rod-coil diblock copolymer poly(acrylic acid)-block-poly(3-hexylthiophene) comprising 21-arm inner coil-like PAA blocks and outer rod-like conjugated polymer poly(3-hexylthiophene) (P3HT) blocks with well-defined molecular structures and narrow molecular weight distribution is synthesized. First, the bromide end-groups of 21-arm star-like ATRP coil polymers PtBA-Br are converted successfully into reactive thioacetate end groups by post-functionalization using potassium thioacetate. Subsequently, 21-arm star-like coil polymers PtBA-SCOCH3 react with rod-like vinyl-functionalized P3HT to yield functional star-like rod-coil diblock copolymers PtBA-b-P3HT via thiol-ene click reaction, followed by selective hydrolysis of inner PtBA block into PAA block. The present synthetic approach enables the construction of well-defined star-like conformation with few structural limitations in a facile and highly efficient manner due to the robust and orthogonal nature of the thiol-ene click reaction. It may be extended to produce block copolymers with other topologies, such as cylindrical, hyperbranched, and dendritic structures.

Core@Corona Functional Nanoparticle-Driven Rod-Coil Diblock Copolymer Self-Assembly.

Herein, a novel strategy to overcome the influence of π-π stacking on the rod-coil copolymer organization is reported. A diblock copolymer poly(3-hexylthiophene)-block-poly(ethylene glycol methyl ether methacrylate) (P3HT-b-PEGMA) was synthesized by the Huisgen cycloaddition, so-called "click chemistry", combining the PEGMA and P3HT blocks synthesized by atom transfer radical polymerization and Kumada catalyst transfer polymerization, respectively. Using a dip-coating process, we controlled the original film organization of the diblock copolymer by the crystallization of the P3HT block via π-π stacking. The morphology of the P3HT-b-PEGMA films was influenced by the incorporation of gold nanoparticles (GNPs) coated by poly(ethylene glycol) ligands. Indeed, the crystalline structuration of the P3HT sequence was counterbalanced by the addition in the film of gold nanoparticles finely localized within the copolymer PEGMA matrix. Transmission electron microscopy and time-of-flight secondary ion mass spectrometry analysis validated the GNP homogeneous localization into the compatible PEGMA phase. Differential scanning calorimetry showed the rod block crystallization disruption. A morphological transition of the self-assembly is observed by atomic force microscopy from P3HT fibrils into out-of-plane cylinders driven by the nanophase segregation.

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.

Molecular theory of liquid-crystal ordering in rod-coil diblock copolymers.

Molecular-statistical theory of rod-coil diblock copolymers is proposed using the general density functional approach which enables one to consider the cases of both weak and strong segregation. The free energy of the system is expressed as a functional of the phase-space densities of rod and coil monomers, which depend on the orientational and translational order parameters. Temperature-concentration phase diagrams are obtained and the profiles of all order parameters are calculated numerically by minimizing the polymer free energy. The lamellar phase is shown to possess strong orientational order which is partially induced by the phase structural anisotropy. The enhanced stability of the lamellar phase is determined by a combination of the microphase separation effects and the emergence of long-range smectic order.

Mechanism for the Self-Assembly of Hollow Micelles from Rod-Coil Block Copolymers

The mechanism for the self-assembly of hollow micelles from rod-coil diblock copolymers is proposed. In a coil-selective solvent, the diblock copolymers self-assemble into a layered structure. It is assumed that the rigid rods form an elastic shell whose properties are dictated by a bending energy. For a hollow micelle, the coils outside the micelle form a brush, while the coils inside the micelle can be in two different states, a brush or an adsorption layer, corresponding to symmetric or asymmetric configurations, respectively. The total energy density of a hollow micelle is calculated by combining the interfacial energy, elastic bending energy and the stretching energy of the brushes. For the asymmetric configuration with a polymer brush on one side, the competition between the elastic bending energy and the brush stretching energy leads to a finite spontaneous curvature, stabilizing hollow spherical micelles. Comparison of the free energy density for different geometries demonstrates that transitions for the different geometry micelles are controlled by the degree of polymerization of the coils and the length of the rods. These results are in agreement with the experimental results.

Phase Diagram of Rod-Coil Diblock Copolymers: Dissipative Particle Dynamics Simulation

Using dissipative particle dynamics, a refined phase diagram of the rod-coil diblock copolymer is constructed in coordinates copolymer composition–repulsion parameter of different types of units. The diagram describes the microphase separation of copolymer blocks and the orientational ordering of rigid blocks. Simulation of rodlike blocks as rigid bodies makes it possible to reduce computational costs, increase the size of the simulation cell to 32 × 32 × 32 and the total length of the copolymer chain N to 20, to vary the composition of the copolymer chain with a smaller step (up to 0.05), and to investigate the behavior of systems with high degrees of segregation of blocks (up to χN ≈ 250). Owing to this optimization, the ordering of rigid blocks not only in the lamellar but also in bicontinuous morphology can be observed for the first time. It is also shown that the zigzag and bilayer lamellas described not only in numerical but also in laboratory experiments are metastable and disappear with an increase in the size of the simulated system.

Elastic properties of liquid-crystalline bilayers self-assembled from semiflexible-flexible diblock copolymers.

The mechanical response and shape of self-assembled bilayer membranes depend crucially on their elastic properties. Most of the studies focused on the elastic properties of fluid membranes, despite the ubiquitous presence of membranes with liquid-crystalline order. Here the elastic properties of liquid-crystalline bilayers self-assembled from diblock copolymers composed of a semiflexible block are studied theoretically. Specifically, the self-consistent field theory (SCFT) is applied to a model system composed of semiflexible-flexible diblock copolymers dissolved in flexible homopolymers that act as solvents. The free energy of self-assembled tensionless bilayer membranes in three different geometries, i.e. planar, cylindrical and spherical, is obtained by solving the SCFT equations using a hybrid method, in which the orientation-dependent functions are treated using the spherical harmonics, whereas the position-dependent operators are treated using the compact difference schemes. The bending modulus κM and Gaussian modulus κG of the bilayer are extracted from the free energies. The effects of the molecular parameters of the system, such as the chain rigidity and the orientational interaction, are systematically examined.