Phase Behavior of Ternary Systems Involving a Conformationally Variable Chain and a Randomly Coiled Polymer

Brownian molecular dynamics simulation on self-assembly behavior of diblock copolymers: influence of chain conformation

Brownian molecular dynamic simulations are applied on the self-assembly behavior of AB-type diblock copolymers. The influence of chain conformation of core-forming A-block changing from rigid to flexible on the aggregation structure formed by AB copolymers is investigated. It is found that at a high rigid fraction f(R) of A-block, a disk structure can be formed at a high aggregation interaction epsilon(AA) of A-bead pairs because of the tendency of orientational packing of rigid portion within the aggregate core. Transitions of aggregation structure from disk to string, further to small aggregates, and to unimers are observed with decreasing epsilon(AA). The packing of A-blocks becomes more random at relatively lower values of f(R), resulting in the formation of spherical structure. The region of string becomes narrower while the regions of the small aggregates and sphere become wider as decreasing f(R). Meanwhile, the onsets of string, disk, and sphere formation move to higher epsilon(AA). The phase diagrams for the influences of rigid potion location within the A-block and the chain rigidity of the A-block are mapped. The comparison of simulation results with existing experimental observations is also presented. Our simulation results tend to bridge a gap of different micellization behaviors between rod-coil block copolymers and coil-coil block copolymers and extend to investigate chain conformation influence on phase diagram.

Microphase separation of rod-coil diblock copolymer in solution

Lattice theory of rigid rods is extended to describe the microphase separation behavior of a rod-coil diblock copolymer in solution. The free energy was formulated by inclusion of the energy terms arising from the core-corona interface between the rods and coils and the corona formed by the coils into the lattice model of rigid rods. The rod-coil diblock copolymer exhibits lyotropic mesophases with lamellar, cylindrical, and spherical structures when the copolymer concentration is above a critical value. The tendency of the rodlike blocks to form orientational order plays an important role in the formation of lyotropic phases. Influences of polymer-solvent interaction, surface free energy, and molecular architectures of the rod-coil diblock copolymer on the phase behaviors were studied, and phase diagrams were mapped accordingly. The theoretical results were compared with some existing experimental observations and a good agreement is shown.