Small Grant for Exploratory Research: A Novel Application of Total Internal Reflection Microscopy: Electrokinetic Lift

全内反射显微镜（TIRM）是一种新技术，可以测量单个胶体粒子和平板之间的相互作用力。在这种技术中，激光束以很小的入射角从玻片上反射出去，这样光就不会通过玻片折射，而只会被反射。这种全内反射产生一种消失的波，它确实向表面垂直传播。将含有胶体粒子的溶液，封闭在一个腔室中，放在玻片上，胶体粒子散射倏逝波。散射强度随粒子与壁面的分离距离呈指数衰减。通过光电倍增管测量散射强度，可以测量粒子与波的瞬时分离距离。PI已经使用这种技术来测量重力和双层力对胶体粒子从表面平衡分离的影响。目前的努力将该技术扩展到粘性流动过程中胶体力的测量。具体来说，PI建议使用该方法来测量流体流过板时胶体颗粒与板的分离距离。将使用辐射压力来固定球体，以便可以测量散射强度，并因此得到一个静止的胶体颗粒的分离距离的结果，该颗粒周围有流体流动。PI已经发展出一套电流体力学理论来解释施加在胶体粒子上的力。这些计算揭示了升力的存在，这种升力使球体远离板壁而不管表面电荷是多少。在没有双层力的情况下，升力等于零。借助TIRM实验，PI希望验证电动升力的存在。

Total Internal Reflection Microscopy (TIRM) is a new technique which allows for the measurement of interaction forces between a single colloid particle and a flat plate. In this technique, a laser beam is reflected off of a glass slide at a small angle of incidence such that light is not refracted through the plate, but only reflected. This total internal reflection produces an evanescent wave which does propagate normal to the surface. A solution containing colloid particles, enclosed in a chamber, is placed on the glass slide, and the colloid particles scatter the evanescent wave. The scattering intensity decays exponentially with the separation distance of the particle from the wall. The scattering intensity is measured by a photomultiplier tube, and from this measurement, the instantaneous separation distance of the particle from the wave can be measured. The PI has used this technique to measure the effects of gravity and double layer forces on the equilibrium separation of a colloid particle from a surface. The present effort extends the technique to the measurement of colloid forces during viscous flow. Specifically, the PI proposes using this method to measure colloid particle - plate separation distances when fluid is flowing across the plate. Radiation pressure will be used to immobilize the sphere so that scattering intensity can be measured, and results will therefore be obtained for separation distances of a stationary colloid particle with fluid streaming about the particle. The PI has already developed an electrohydrodynamic theory for the forces exerted on the colloid particle. These calculations reveal the existence of a lift force which causes the sphere to migrate away from the plate wall irrespective of the surface charge. In the absence of double layer forces, this lift force is equal to zero. With the aid to the TIRM experiments, the PI hopes to verify the existence of the electrokinetic lift force.