Phoio-Switchable Surface Topologies in Chiral Nematic Coatings

摘要

Control of the surface topology in the micrometer range by active switching between two states is of interest for a wide variety of applications. For instance, a topology-modulated change in the friction coefficients finds its application in the field of haptics where robotic manipulation and touch-input devices are of importance. Also the optical properties are strongly affected by changes of the surface topology, for example, the directionality of diffusive reflection or the modulation of diffractive properties. We can also think of even more advanced applications such as switchable wettability or adhesion control as, for example, the adhesion induced by geckos climbing surfaces. Furthermore, in micro-fluidic applications diffusion and fluid mixing can be substantially enhanced by introducing microscopic topologies on the surface. In many current implementations the switching of the surface topology is triggered by an electric field using electrostatic or piezoelectric effects. This requires the direct vicinity of electrodes and wires for driving the process. Alternatively, thermal effects based on thermal expansion effects or phase transitions can be used. In buffer solutions surface switching is established in hydrogels by either pH or thermal effects and is often proposed to control protein or cell adhesion in biological systems.