Electrophoresis in Liquid Crystals

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TECHNICAL SUMMARY The proposed research focuses on electrophoresis in liquid crystals. Electrophoresis is a motion of charged dispersed particles relative to a fluid in a uniform electric field. The effect is widely used to separate macromolecules such as DNA and proteins, to assemble colloidal structures, to transport particles in nano- and microfluidic devices and ePaper type of displays. Typically, the fluid is isotropic (for example, water) and the electrophoretic velocity is linearly proportional to the electric field. It has been recently demonstrated that when the electrophoresis is performed in a liquid-crystalline nematic fluid, the effect becomes strongly nonlinear, with a velocity component that is quadratic in the applied voltage [O. D. Lavrentovich, I. Lazo, O. P. Pishnyak, Nonlinear electrophoresis of dielectric and metal spheres in a nematic liquid crystal, Nature 467, 947-950 (2010)]. The goal of this project is to explore the fundamental physical mechanisms controlling the LC electrophoresis, establish the role of LC orientational order, anisotropy of dielectric and electroconductive properties, determine the flow patterns around an electrophoretic particle, explore the phenomenon as the function of amplitude and frequency of the driving voltage, type of the liquid crystal carriers and the particles. NON-TECHNICAL SUMMARY Electrically-induced transport of particles in fluids is an important phenomenon with applications ranging from e-readers such as Kindle to health sciences, where it is used in separation of DNA molecules and proteins, antibiotic and vaccine analysis. In regular fluids (such as water) a particle can move parallel to the field direction when it is electrically charged. This project explores a new type of electrophoresis that occurs when the particle moves in a liquid crystal rather than in a regular fluid. The ordered structure of the liquid crystal brings an entirely new dimension to the effect. For example, particles that cannot move in a regular fluid (say, because their electric charge is zero) acquire the ability to move once the medium has a liquid crystalline order. The project will explore the basic mechanisms and feature of the electrically induced motion of microparticles in liquid crystals. The phenomenon offers new perspectives for practical applications where highly flexible, precise and simple control of particle (or cargo) placement, delivery, mixing or sorting is needed. The research will offer new insights for the display technology, colloidal assembly, sorting, microfluidic and micromotor applications.