Electrophoresis in Liquid Crystals

技术综述建议的研究重点是液晶中的电泳法。电泳法是带电分散颗粒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，在纳米和微流控设备以及电子纸类型的显示器中传输粒子。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正比。最近已经证明，当在液晶向列相流体中进行电泳时，该效应变得强烈的非线性，速度分量在施加的电压中是二次的[O.D.Lavrentovich，I.Lazo，O.P.Pishnyak，在向列相液晶中的介电和金属球体的非线性电泳，自然，467,947-950(2010)]。本项目的目标是探索控制液晶电泳的基本物理机制，确定液晶取向顺序、介电和导电性质的各向异性的作用，确定电泳颗粒周围的流动模式，探索作为驱动电压的幅度和频率、液晶载体类型和颗粒的函数的现象。非技术概述电诱导颗粒在液体中的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，在健康科学中，它被用于DNA分子和蛋白质的分离、抗生素和疫苗分析。在常规流体(如水)中，粒子带电时可以平行于电场方向运动。这个项目探索了一种新型的电泳，当粒子在液晶中运动时，而不是在常规流体中。液晶的有序结构为这种效果带来了一个全新的维度。例如，不能在常规流体中运动的粒子(例如，因为它们的电荷为零)一旦介质具有液晶秩序，就获得了运动的能力。该项目将探索微粒子在液晶中电诱导运动的基本机制和特征。这一现象为实际应用提供了新的视角，在这些应用中，需要高度灵活、精确和简单地控制颗粒(或货物)的放置、输送、混合或分拣。这项研究将为显示技术、胶体组装、分选、微流控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.