Liquid crystalline assembly of rod-coil diblock copolymer and homopolymer blends by dissipative particle dynamics simulation.

ABSTRACT

Liquid crystalline assembly of rod-coil diblock copolymers blended with coil or rod homopolymers is investigated by dissipative particle dynamics simulation, considering systematically the effect of the interactions between rods and coils, the volume fraction and length of the added coil or rod homopolymers. The addition of coil or rod homopolymers induces disorder-order or order-liquid crystalline transition. In rod-coil/coil blends, the solubilization of homopolymers will saturate at a certain amount of homopolymers and then the excess homopolymers will be segregated into the central regions of coil block domains, forming "wet-dry mixture" lamellae. The solubility capacity decreases with increasing homopolymer length, determined by the competition between the mixing entropy and the elastic entropy. In rod-coil/rod blends, due to the orientational interactions between rods, the length matched rod homopolymers directly interdigitate with rod blocks with less entropy loss, thus prompting the formation of a bilayer liquid crystalline phase. The rod domain spacing Dr remains unchanged and conversely the coil domain spacing Dc becomes thin, to occupy more interfacial area. With the addition of shorter rod homopolymers, the overall lamellar spacing D of blends monotonically increases with the volume fraction of homopolymers, similar to the case of rod-coil/coil blends. Generally, rod homopolymers have a more significant impact on the liquid crystalline assembly of the blends, compared with the coil homopolymers. Our results indicate that blending with coil or rod homopolymers into a rod-coil system is an effective method to induce liquid crystal phase transition and control the phase spacing of the ordered structure.