Using the "Switchable" Quality of Liquid Crystal Solvents To Mediate Segregation between Coil and Liquid Crystalline Polymers

Abstract

The discontinuous change in solvent quality of a liquid crystal (LC) solvent, 5CB, at the nematic−isotropic phase transition produces abrupt changes in the phase behavior of solutions of coil and LC polymers and in the self-assembly of coil−LC block copolymers. Nematic 5CB is strongly selective for a side-group liquid crystal polymer (SGLCP), and isotropic 5CB is a good solvent for both SGLCP and a random coil (polystyrene, PS). In nematic 5CB, unfavorable LC−PS interactions drive phase separation in SGLCP−PS−LC ternary solutions and drive micellization of PS−SGLCP diblocks. In isotropic 5CB, rich phase behavior occurs in both ternary solutions and block copolymer solutions. Despite the fact that isotropic 5CB is a good solvent for both SGLCP and PS, segregation can occur due to the asymmetric solvent effect (i.e., the preference of the solvent for the SGLCP). In concentrated isotropic solutions, unfavorable SGLCP−PS interactions become dominant.

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