Liquid crystalline gels self-assembled from block copolymers

Abstract

Self-assembly of coil-SGLCP-coil block copolymers provides a route to model liquid crystalline (LC) gels in concentrations ranging from bulk polymer to gels with as little as 5 wt % polymer in a small-molecule LC host. Triblock copolymers with LC-phobic endblocks associate in a nematic liquid crystal to create crosslinks. An SGLCP midblock allows for solubilization of the network. These materials have a precisely tailored network structure ideal for comparison to theory1 of liquid crystalline elastomers. In addition, the gel responds readily to external fields since the concentration of polymer can be relatively low. In this report we discuss rheological measurements that demonstrate gelation at low polymer concentrations. We show that the association of the PS blocks at low concentration is driven by the presence of the SGLCP, rather than incompatibility between PS and 5CB. We then discuss the alignment of the gels via shear, magnetic fields, electric fields, and alignment surfaces. Finally, we present results on a distinctive striped texture observed in aligned gels when subjected to an applied electric field or normal force. The exceptional electro-optic and mechano-optic responsiveness of these gels coupled with thermally reversible gelation suggests they would be ideal candidates for use in large-area printable display technology.