Capacitive transduction for liquid crystal based sensors in ordered and partially disordered systems.

摘要

This dissertation investigates a capacitive transduction technique for use in liquid crystal (LC) based sensors with potential applications to chemical and biological systems. The capacitive transduction in LC based sensors exhibits a change in capacitance in response to a change in the molecular deformation in the LC film. The objectives of this research are to provide insight into the molecular behavior inside the LC film and to track the average molecular distortion (the director axis) and the degree of the orientational order (the order parameter) in ordered and partially disordered LC based sensors via capacitive transduction.; Toward these objectives, the dissertation starts by studying the mechanism of the capacitive transduction in tracking the director axis of a nematic ordered LC film. Practical sensor implementations utilizing interdigitated electrodes are designed, fabricated and tested to be used as LC based sensors. The ability of these sensors involving the capacitive transduction technique to track the director axis has been investigated and experimentally verified. It is proven that two orthogonal capacitance measurements can uniquely track the director axis in an ordered LC film.; The dissertation continues by investigating the extension of these sensors to track the director axis orientation and the order parameter in partially disordered LC films. A slight change to the previous implementations is added so these sensors can still be used to track the molecular deformation when a reduction in the degree of order inside the LC film occurs. In this case, three capacitance measurements are required to uniquely track the LC director as well as the order parameter. The sensitivity of the sensor is also studied in all the previous cases. It is shown that the sensor structure, the initial state of the molecular orientation and the degree of order, impact the capacitive transduction sensitivity.; The dissertation finishes by demonstrating the procedure followed and the materials used to fabricate and test these sensors. All fabrication and testing steps were done in the UAH clean room facility. The experimental results are shown to match the theoretical and simulation results.