In this research, homogeneous electro-rheological (ER) fluids based on liquid crystalline polymers (LCPs) are characterized experimentally in pressure-driven flow between narrowly separated electrodes. The objective of this work is to develop a quantitative understanding of homogeneous ER fluids in complex flow geometries, in order to assess the technical feasibility of using the fluids in conventional and microfluidic applications. The project scope consists of three parts: (1) synthesis of the LCP, (2) experimental characterization and quantitative mechanistic modeling of the ER behavior of LCP solutions, and (3) testing of the LCP solutions in simple and complex fabricated channels. Poly(n-hexyl isocyanate) (PHIC) is synthesized by living, reversible polymerization to produce monodisperse samples various molecular weights. The viscosity of concentrated solutions of PHIC is experimentally characterized over a range of shear rates and electric field strengths, and modeled with a previously developed two-dimensional version of Doi's molecular theory of LCP rheology. Steady state and transient pressure drop measurements at constant flow rate are conducted in rounded-entry channels. Special micro-electrodes are fabricated by electron beam lithography in an overlay pattern in order to direct two-dimensional planar ER fluid flow in a prescribed fashion by selective electrification of electrodes. This work will allow, for the first time in 50 years of ER fluid research, the complete a priori prediction of ER behavior from the properties of the fluid components. This predictive capability links ER fluid formulation with ER device design, so that rigorous engineering analysis can identify which fraction of the estimated potential billion dollar market for ER devices can be realized using homogeneous ER fluids.
