Optical modulation of cholesteric structures using microfluidics

Materials that produce color changes in response to stimuli are interesting for applications such as sensing and camouflage. 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. Their response to pressure-driven flow in microfluidic channels has however remained experimentally unexplored. 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. 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.