The Self-assembly Of Diblock Copolymers Under The Enviromentof Selective Solvents And Blends

The aggregation behavior of cyclic rod-coil (RC) diblock copolymer in dilute solutions is investigated by dissipative particle dynamics simulation (DPD). With varying the rod length and coil length, the cyclic RC copolymer in coil-selective solvent exhibits various morphologies,including spherical micelle, vesicle, bilayer disc and ribbon bundle structure. Compared with the equivalent linear RC copolymer, only spherical micelle and barrel bundle phase are observed. The rod length is the major factor controlling the liquid-crystalline behavior of RC copolymer systems, while the coil length has a secondary effect on the aggregate morphology. Especially for the end-to-end ribbon bundle and side-by-side barrel bundle, which are assembled by cyclic and linear RC copolymer solutions, respectively, the size of rod bundle varies with the coil length. It indicates that the ribbon bundle or nanofiber-like structure in cyclic RC copolymer can be obtained by efficiently selecting the rod length and coil length, and the optical and electrical properties of RC copolymer would be further controlled and optimized. Additionally, with varying the solvent quality from coil-selective to neutral to rod-selective,rich nanostructures of cyclic RC copolymer are observed, significantly different from the case of linear counterpart. The result illustrates the cyclization of a linear RC copolymer induces remarkable differences in the rod arrangement and aggregation behavior, thereby indicating the competition between interfacial energy, rod orientational entropy, coil stretching entropy, and packing constraints.Secondly, the liquid-crystal assembly of semiflexible-coil diblock copolymers and (coil or semiflexible) homopolymers blends is studied by using the dissipative particle dynamics simulation. Phase diagrams of the blends and the orientation parameters between semiflexible blocks are constructed as a function of the homopolymer volume fraction and semiflexible chain stiffness. For semiflexible-coil/coil blends, we verified the results on the systems varied from coil-coil/coil to rod-coil/coil blends.Not only the "dry brush" induced by coil homopolymers, but also the disorder-lamellae or lamellae-liquid crystalline transition, is clearly observed. For semiflexible-coil/semiflexible blends, the addition of semiflexible homopolymers also leads to the disorder-order transition,and even causes the transition between monolayer and bilayer smectic-A phases (liquid crystalline phase). Besides, we can utilize one of the chain stiffness of block and homopolymer to template the orientation ordering of the other one with weak rigidity. In general, this work could provide valuable guidance in manipulating the liquid-crystal assembly of polymer with weak chain rigidity.