(482i) Flow-Induced Morphological Changes in Strongly Chiral Systems

Controlling fluid flow in confined geometries is one of the most versatile strategies to manipulate molecular organization in soft matter. Liquid crystals represent one of the most attractive and ideal soft matter systems for the study of non-equilibrium behaviors as they produce color changes in response to stimuli which is of interest for applications such as sensing and camouflage. In past studies of liquid crystal flow in microfluidic channels, we focused mostly on the nematic phase, which is the simplest liquid crystalline state. The flow of complex cholesteric liquid crystals in microchannels has however remained experimentally unexplained. Cholesteric liquid crystals are a unique class of soft materials as they exhibit self-assembled helical structures sensitive to various external stimuli and are known for their selective light reflection. Here, we study a cholesteric system that has a helical pitch comparable to the wavelength of visible light and can therefore exhibit structural coloration. Before the application of flow, the color of the cholesteric phase is independent of temperature but after flow alignment, a blue-shift is observed upon increasing temperature. New cholesteric textures are created in flow. We observe that flow creates stable-colored bands, which remain stable for months. Our work identifies a strategy to generate stimuli-responsive materials in low volume. As highly cholesterics can form blue phases, we will also show flow-induced out-of-equilibrium regimes of blue phases when subject to a pressure-driven flow in a confined geometry. The flow-structure relationships revealed by our study could be relevant to applications such as additive manufacturing of LCs which involve manipulating these fluids in microchannels.