Design of Responsive and Active (Soft) Materials Using Liquid Crystals

Liquid crystals (LCs) are widely known for their use in liquid crystal displays (LCDs). Indeed, LCDs represent one of the most successful technologies developed to date using a responsive soft material: An electric field is used to induce a change in ordering of the LC and thus a change in optical appearance. Over the past decade, however, research has revealed the fundamental underpinnings of potentially far broader and more pervasive uses of LCs for the design of responsive soft material systems. These systems involve a delicate interplay of the effects of surface-induced ordering, elastic strain of LCs, and formation of topological defects and are characterized by a chemical complexity and diversity of nano- and micrometer-scale geometry that goes well beyond that previously investigated. As a reflection of this evolution, the community investigating LC-based materials now relies heavily on concepts from colloid and interface science. In this context, this review describes recent advances in colloidal and interfacial phenomena involving LCs that are enabling the design of new classes of soft matter that respond to stimuli as broad as light, airborne pollutants, bacterial toxins in water, mechanical interactions with living cells, molecular chirality, and more. Ongoing efforts hint also that the collective properties of LCs (e.g., LC-dispersed colloids) will, over the coming decade, yield exciting new classes of driven or active soft material systems in which organization (and useful properties) emerges during the dissipation of energy.