Electrophoresis in Liquid Crystals

所提出的研究集中在液晶中的电泳。 电泳是带电的分散粒子在均匀电场中相对于流体的运动。这种效应被广泛用于分离DNA和蛋白质等大分子，组装胶体结构，在纳米和微流体设备以及ePaper类型的显示器中传输颗粒。通常，流体是各向同性的（例如，水），并且电泳速度与电场成线性比例。最近已经证明，当在液晶微流体中进行电泳时，该效应变得强烈非线性，具有在所施加的电压中为二次的速度分量[O. D.拉夫连托维奇岛拉佐岛P. Pishnyak，Nonlinear electrophoresis of dielectric and metal spheres in a pixel liquid crystal，Nature 467，947-950（2010）]。 本研究的目的是探索控制液晶电泳的基本物理机制，建立液晶取向有序、介电各向异性和介电常数的作用，确定电泳粒子周围的流动模式，探索这种现象与驱动电压的幅度和频率、液晶载体和粒子类型的函数关系。流体中颗粒的电诱导传输是一种重要的现象，其应用范围从电子阅读器（如Kindle）到健康科学，其中其用于DNA分子和蛋白质的分离、抗生素和疫苗分析。 在规则的流体（如水）中，当粒子带电时，它可以平行于场的方向移动。 该项目探索了一种新型的电泳，当粒子在液晶中而不是在常规流体中移动时发生。 液晶的有序结构为这种效果带来了全新的维度。 例如，不能在常规流体中移动的粒子（比如说，因为它们的电荷为零）一旦介质具有液晶有序性，就获得了移动的能力。 本计画将探讨液晶中微粒子电诱导运动的基本机制与特性。 这种现象为实际应用提供了新的视角，其中需要高度灵活，精确和简单地控制颗粒（或货物）的放置，输送，混合或分选。 该研究将为显示技术，胶体组装，分选，微流体和微电机应用提供新的见解。

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.