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.

Extrusion, electrospinning, and microdrawing are widely used to create fibrous polymer mats, but these approaches offer limited access to oriented arrays of nanometer-scale fibers with controlled size, shape, and lateral organization. We show that chemical vapor polymerization can be performed on surfaces coated with thin films of liquid crystals to synthesize organized assemblies of end-attached polymer nanofibers. The process uses low concentrations of radical monomers formed initially in the vapor phase and then diffused into the liquid-crystal template. This minimizes monomer-induced changes to the liquid-crystal phase and enables access to nanofiber arrays with complex yet precisely defined structures and compositions. The nanofiber arrays permit tailoring of a wide range of functional properties, including adhesion that depends on nanofiber chirality.

It is demonstrated that aqueous dispersions of micrometer-sized liquid crystal (LC) droplets provide the basis of a general and facile methodology for the templated synthesis of spherical and nonspherical polymeric microparticles with complex internal structure and porosity. Specifi cally, nematic droplets of reactive (RM257)/nonreactive mesogens with distinct internal confi gurations are prepared using a range of approaches, the reactive mesogens are photopolymerized, and then the nonreactive mesogens are extracted to yield polymeric particles. It is found that LC droplets exhibiting bipolar, radial, axial or preradial confi gurations template the formation of spindleshaped, spherical, spherocylindrical or tear-shaped polymeric microparticles, respectively. Each type of microparticle exhibits distinct optical signatures indicating the presence of an internal LC-templated, anisotropic polymer network. In addition, by using a microfl uidic system to generate monodisperse LC droplets containing 10%-40% wt/wt of RM257, spindle-shaped microparticles with tailored aspect ratios ranging from 2.4 to 1.2 are formed. The mass density of spherical microparticles templated from radial LC droplets can be tuned to range from 0.2 to 0.6 g cm −3 , revealing the introduction of porosity (confi rmed by electron microscopy) with a volume-average pore diameter of 39 ± 16 nm (obtained from nitrogen sorption isotherms).

We report the fabrication of chemically patterned microwells that enable the rapid and facile preparation (by spin coating and patterned dewetting) of thin films of liquid crystals (LCs) that have precise thicknesses (0.7-30 μm), are supported on chemically defined substrates, and have free upper surfaces. We use these microwells to prepare elastically strained nematic LC films supported on silica glass, gold, or polystyrene substrates and thereby characterize the response of the strained LC films to vapors of toluene. We report that low concentrations of toluene vapor (<500 ppm) can partition into the LC to lower the anchoring energy of the LC on these substrates, thus allowing the elastic energy of the strained LC film to drive the LC films through an orientational transition. The central role of the toluene-induced change in surface anchoring energy is supported by additional experiments in which the response of the nematic LC to changes in film thickness and substrate identity are quantified. A simple thermodynamic model captures these trends and yielded estimates of anchoring energies (8-22 μJ/m(2)). Significantly, the orientational transitions observed in these strained LC thin films occur at concentrations of toluene vapor that are almost 1 order of magnitude below those which lead to bulk phase transitions, and they are not triggered by exposure to water vapor. Overall, these results hint at principles for the design of responsive LC-based materials that can be triggered by concentrations of aromatic, volatile organic compounds that are relevant to human health.

Characterization of the phase behaviour of cholesteric and BPsTo characterize the phase behavior of the LC mixture containing 32.5 wt. % of S-811, we placed the LC between two glass slides separated by 18 um thick spacers. The sample was mounted onto a heated stage and observed under a light microscope using crossed-polarizers. The initial observations of the cholesteric LC were made using transmitted-light and a representative image is shown in Figure S1a. This image, obtained at room temperature (26.0 °C), shows the characteristic Grangjean texture of a cholesteric with planar anchoring conditions at the top and bottom interfaces with glass. The optical texture of the cholesteric changed little until the temperature was increased to 47.5 °C, at which point the sample abruptly lost birefringence and appeared dark when viewed using transmitted light. However, when the sample was imaged using reflected light, brightly colored granular domains with blue and red colors were observed at 47.5 °C (Figure S1b). This optical texture persisted as the temperature was increased to 48.7