Liquid crystalline block copolymers for macroscopic nanodomain orientation and photoinduced microphase separation

Abstract

We report the design and study of new liquid crystalline block copolymers (LC-BCPs) with which unusual properties and functions can be obtained. On the one hand, we prepared the first LC-BCP comprising regioregular poly(3- hexylthiophene) (P3HT) and a side-chain liquid crystalline polymer (SCLCP) bearing azobenzene mesogens (PAzoMA). With the SCLCP block having a clearing temperature above the high crystal melting temperature of P3HT, surface- and photoinduced orientation of mesogens in PAzoMA can be used to align stripe nanodomains of P3HT on a macroscopic scale. This study demonstrates a promising pathway to achieving and manipulating macroscopically ordered nanodomains of π-conjugated polymers. On the other hand, by using a rationally designed diblock copolymer composed of two SCLCPs, photoinduced microphase separation in BCPs was achieved for the first time. In this case, the miscibility of the two LC blocks is promoted by the miscibility between the two types of mesogenic side groups, while upon UV light irradiation inducing the trans-cis isomerization of azobenzene mesogens on one block, the shape incompatibility of bent cis isomers with an ordered LC phase drives the two blocks to separate from each other resulting in a microphase separated morphology. This study shows the perspective of using light to process and organize BCP morphology and related nanostructures in a lithography-free manner.