Molecular Architecture Effect on Microphase Separation in Supramolecular Comb−Coil Complexes of Polystyrene-block-poly(2-vinylpyridine) with Dodecylbenzenesulfonic Acid: AnBn Heteroarm Star Copolymer

Impact of chain microstructure on solution and thin film self-assembly of PCHD-based semi-flexible/flexible diblock copolymers

Self-assembly of semi-flexible/flexible block copolymers in a selective solvent is examined using a set of diblock copolymers where the chain microstructure of the semi-flexible block is manipulated in order to tune chain stiffness. Conceptually, the reduced conformational space of the semi-flexible block is anticipated to alter the way the chains pack, potentially changing the structure of self-assembled aggregates in comparison to flexible diblock copolymer analogs. Semi-flexible/flexible diblock copolymers comprised of poly(styrene)-block-poly(1,3-cyclohexadiene) (PS-b-PCHD) having systematic changes in chain microstructure, as captured by the ratio of 1,4/1,2-linkages between cyclohexenyl repeat units, and molecular weight of the PCHD blocks were synthesized using anionic polymerization. These diblocks were dissolved in tetrahydrofuran (THF), which is a preferential solvent for PS, and the structures formed were examined using laser light scattering and complementary imaging techniques. Results show that PS-b-PCHD copolymers with a chain microstructure of 90% 1,4/10% 1,2 linkages between cyclohexenyl repeat units (referred to simply as 90/10) are able to micellize, forming spherical structures, while diblocks of 70/30 and 50/50 1,4-to-1,2 ratios remain as single chains and ill-defined aggregates, respectively, when dissolved in THF. With inferences drawn from simple structural models, we speculate that this self-assembly behavior arises due to the change in the chain configuration with increasing content of 1,2-links in the backbone. This renders the chain with higher 1,2 content incapable of swelling in response to solvent and unable to pack into well-defined self-assembled structures.

Self-assembly of block copolymer-based ionic supramolecules based upon multi-tail amphiphiles

Using synchrotron small angle X-ray scattering (SAXS), self-assembly of ionic supramolecules based upon diblock copolymers of poly(styrene)-b-poly(methacrylic acid) and multi-tail (2- or 4-tail) alkyl quaternary ammonium amphiphiles is investigated.

thin films of poly(isoprene-b-ethylene oxide) diblock copolymers on mica: an atomic force microscopy study

The structural behavior of three amphiphilic semicrystalline poly(isoprene-b-ethylene oxide) block copolymers (PI-b-PEO) with different PEO volume fraction (f(PEO) = 0.32, 0.49, and 0.66), spin-coated on freshly cleaved mica surfaces from aqueous solutions, was investigated by atomic force microscopy. We focus on the dependence of the resulting thin film nanostructures on the molecular characteristics (f(PEO) and molecular weight) and the adsorbed amount. The nanostructures obtained immediately after spin-coating were robust and remained unchanged after annealing and/or aging. The PEO affinity for the highly hydrophilic mica and the tendency of the hydrophobic and low surface energy PI to dewet and be at the free interface caused the soft PI-b-PEO micelles to collapse leading to the formation of 2D dendritic networks over mica. We show that, for all three polymers, the dendritic monolayer thickness can be predicted by a model consisting of a PEO crystallized layer (directly on top of mica) of the same thickness in all cases and a PI brush layer on top. In thicker areas, polymer material self-assembled into conelike multilamellar bilayers on top of the monolayer and oriented parallel to the substrate for both symmetric and asymmetric diblock copolymers with the lowest f(PEO). We compare the lateral morphology of the films and discuss the thickness heterogeneity, which results from the coupling and competition of crystallization kinetics, phase separation, and wetting/dewetting phenomena highlighting the role of the two blocks to inhibit or enhance certain morphologies. We show that the deviation of the f(PEO) = 0.32 thin film from its bulk phase structure (cylinders in hexagonal lattice) continues for several lamellar bilayers away from the substrate. For the asymmetric PI-b-PEO polymer with the higher PEO volume fraction (f(PEO) = 0.66) and higher APT, laterally extensive stacks of flat-on lamellar crystallites formed on the surface demonstrating the crucial role of the PEO crystallization.

Tailoring of the hierarchical structure within electrospun fibers due to supramolecular comb-coil block copolymers: polystyrene-block-poly(4-vinyl pyridine) plasticized by hydrogen bonded pentadecylphenol

Previously we demonstrated hierarchical self-assembly and mesoporosity in electrospun fibers using selected polystyrene--poly(4-vinylpyridine) (PS--P4VP) diblock copolymers with hydrogen-bonded 3--pentadecylphenol (PDP), which rendered distorted spherical P4VP(PDP) domains within the PS matrix, internal lamellar order within the P4VP(PDP) domains, and allowed distorted spherical pores by removing PDP (. 2005, , 1048). Here we study whether the internal structure of electrospun fibers can be systematically tailored by varying the compositions of PS--P4VP(PDP). We expect these complexes to be feasible choices to combine electrospinning and self-assembly, as relatively high molecular weight block copolymers are useful for electrospinning, and enhanced structure formation due to plasticization by the amphiphilic PDP was expected. Not surprisingly, the self-assembled structures of the as-prepared fibers were less perfect than those in the corresponding well-annealed bulk materials. Compositions that show spherical self-assembly of P4VP(PDP) within the PS matrix in bulk lead to distinct and elongated worm-like P4VP(PDP) domains within the PS matrix in electrospun fibers. More symmetric compositions, which showed lamellar self-assembly in bulk, lead to structures where both PS and P4VP(PDP) domains were worm-like and elongated in a relatively symmetric manner. Finally, compositions which in bulk showed self-assembly of PS spheres within the P4VP(PDP) matrix, lead to separate distorted PS domains in the P4VP(PDP) matrix. Additionally, SAXS measurements suggest a lamellar structure within the P4VP(PDP) domains. As electrospinning is a facile method to prepare mesoscale fibers, and it is known that the amphiphiles can be removed from the hierarchical assemblies, the present method offers the potential to tune the internal porosity of the fibers for release and absorption purposes.

A Self-Consistent Field Theory Study on the Morphologies of Linear ABCBA and H-Shaped (AB)2C(BA)2 Block Copolymers

By using a combinatorial screening method based on the self-consistent field theory, we investigate the equilibrium morphologies of linear ABCBA and H-shaped (AB)(2)C(BA)(2) block copolymers in two dimensions. The triangle phase diagrams of both block copolymers are constructed by systematically varying the volume fractions of blocks A, B, and C. In this study, the interaction energies between species A, B, and C are set to be equal. Four different equilibrium morphologies are identified, i.e., the lamellar phase (LAM), the hexagonal lattice phase (HEX), the core-shell hexagonal lattice phase (CSH), and the two interpenetrating tetragonal lattice phase (TET2). For the linear ABCBA block copolymer, the reflection symmetry is observed in the phase diagram except for some special grid points, and most of grid points are occupied by LAM morphology. However, for the H-shaped (AB)(2)C(BA)(2) block copolymer, most of the grid points in the triangle phase diagram are occupied by CSH morphology, which is ascribed to the different chain architectures of the two block copolymers. These results may help in the design of block copolymers with different microstructures.