Electrokinetics in Liquid Crystals

Kent State University, Kent OH

Investigators

Abstract

Non Technical Abstract Liquid crystals (LCs) represent a peculiar state of matter combining properties of solid crystals and isotropic fluids. The subtle combination of orientational order, fluidity, and eager responsiveness to the electric field featured by the LCs brought a revolution in the way we present information nowadays, enabling an entire industry of portable LC displays. The project focuses on LCs as a functional medium that enables new forms of electrokinetics, i.e., motion of particles and fluids under an externally applied electric field. As compared to standard isotropic fluids such as water, the LCs offer new mechanisms of electrokinetics, rooted in orientational order of molecules. The project explores a new approach to induce and control the electrokinetic flows through surface-imprinted molecular orientation of the LC. The objective is to establish a fundamental understanding of electrokinetics in LCs, determine which new technologies and applications might emerge from the study, and to train the new generation of researcher (graduate students and postdoctoral fellows) in this cutting edge research of technological significance. Technical Abstract Electrokinetics represents a broad spectrum of phenomena associated with a relative motion at fluid/solid interfaces caused by external electric fields that act on suitably separated space charges, such as electric double layers or induced charges. The project goals are to explore a new mechanism of electrokinetics, in which the spatial charges are generated through the coupling of anisotropic electric conductivity to the liquid crystal (LC) director gradients and also to develop a new method to trigger the electrokinetic flows, through the imprinted surface patterns of director gradients. The control of surface alignment is performed locally in each point of the substrate by photo-irradiation. The project advances knowledge of electrohydrodynamics of isotropic fluids and electrohydrodynamics of LCs, two extremely rich scientific branches usually considered separately. It brings a new perspective in a general area of charge transport in organic matter which embraces photosynthesis, transport within proteins and across biomembranes. The project uses well-tested experimental methods such as three-dimensional optical microscopy, microparticle velocimetry, photoalignment and electro-optics, thus ensuring that the new knowledge is based on a solid experimental background. The research advances discovery and understanding of electrokinetics and LCs as materials for applications other than LC displays. The study offers new perspectives for practical applications where highly flexible, precise and simple control of fluid or cargo placement, delivery, mixing or sorting is needed. The research will be conducted at the Liquid Crystal Institute, which will immediately make the results and techniques available to numerous partners already linked together by the Institute's Industrial Partnership Program. The project helps to achieve the educational goals of the 5-Year Federal Science, Technology, Engineering, and Mathematics (STEM) Education Strategic Plan and the Materials Genome Initiative, by preparing the next generation of highly trained science professionals.