Stretchable liquid crystal blue phases Seminar

Liquid-crystals and polymers are materials of considerable scientific and technological interest, and hybrid materials which comprise both a polymer network and liquid-crystalline order—such as liquid crystal elastomers and gels—can not only combine the favourable properties of both but exhibit new properties unseen in either class of material independently, with applications ranging from artificial muscles to optical devices. The properties of the hybrid, and its utility for a given device application, depend crucially on the type of liquid crystal mesophase employed. Stretchable cross-linked liquid crystalline systems have previously been demonstrated in the nematic, chiral nematic, and smectic mesophases, each with unique physical properties and technological potential. In this seminar I will discuss recent work at the University of Cambridge where we have succeeded in fabricating stretchable gels using a liquid crystal blue phase. The material exhibits a number of interesting properties such as strain-induced colour change and a linear electro-optic (Pockels) effect. The latter, which has not been observed in unstrained blue phases, may be an interesting alternative to Kerr switching in low-voltage blue phase electro-optic devices. While the theory of nematic, chiral nematic, and smectic elastomers and gels has been actively investigated for some decades, the theory of blue phase elastomers or gels is currently unexplored; I will discuss some of the theoretical questions raised by our experiments.