Liquid Crystalline Assembly Of Rod–coil Diblock Copolymer And Homopolymer Blends

Liquid crystalline assembly of binary mixture and ternary mixture that rod-coil diblock copolymers blended with flexible coil/rigid rod homopolymers is investigated by dissipative particle dynamics simulation(DPD), 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/rod homopolymers induces disorder-order or order-liquid crystalline transition.In rod-coil/coil binary blends, the solubilization of flexible coil 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 so-called “wet-dry mixture” lamellae. The solubility capacity decreases with increasing coil homopolymer length,determined by the competition between the mixing entropy and the elastic entropy.In rod-coil/rod binary blends, due to the orientational interactions between rigid 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 spacingrD remains unchanged and conversely the coil domain spacingcD 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 rod homopolymers, similar to the case of rod-coil/coil binary blends.Generally, rod homopolymers have a more significant impact on the liquid crystalline assembly of the blends, compared with the flexible coil homopolymers.In rod-coil/coil/rod ternary blends,adding both coil homopolymers and rod homopolymers into the rod-coil copolymer,when some flexible coil homopolymers are replaced by rod homopolymers with the corresponding volume fraction,the system will gradually form the perfect liquid crystalline phase, meanwhile the lamellar spacing D will decrease due to the realignment of coils.In this paper, our results indicate that blending with flexible coil/rigid rod homopolymers into a rod-coil system is an effective methodto induce liquid crystal phase transition and control the phase spacing of the ordered structure.