CAREER: Measuring the Effect of Nano-Scale Charge Nonuniformity on Colloidal Forces

目前对胶体力的理解通常假设粒子上的电荷是均匀分布的。不均匀的电荷分布将显著地改变粒子间的力。研究目标是：纳米级电荷不均匀性将在微米尺寸的单个胶体颗粒上测量;并且胶体颗粒上的电荷不均匀性将与所测量的颗粒之间的法向和切向胶体力相关。这项研究的部分原因是PI最近的数据显示，两个非接触颗粒之间作用的时间依赖性切向胶体力可能是由不均匀的电荷分布引起的。电荷不均匀性对悬浮液稳定性和流变性的建模有重要影响。将结合微电泳实验、电动力学理论和蒙特卡罗模拟来测量单个颗粒上的电荷不均匀性。 粒子上的电荷不均匀性将与粒子之间的力有关。使用最近开发的“差示电泳”技术，可以以亚皮牛顿分辨率测量两个颗粒之间的法向力（那些力沿着中心线作用）和它们之间的切向力（那些力沿颗粒的相邻表面横向沿着作用）。差示电泳可以测量两个布朗粒子之间的粒子间力在间隙小于100纳米，其中货车德瓦尔斯力是重要的。

The current understanding of colloidal forces generally assumes that the charges on particles are uniformly distributed. A nonuniform charge distribution will significantly alter interparticle forces. The research goals are: the nanoscale charge nonuniformity will be measured on individual colloidal particles of micron size; and the charge nonuniformity on colloidal particles will be related to the measured normal and tangential colloidal forces between the particles. This research was prompted in part by recent data from the PI that shows time-dependent tangential colloidal forces acting between two non-touching particles that could result from a nonuniform charge distribution. Charge nonuniformity could have a major impact on the modeling of bulk suspension stability and rheology.The charge nonuniformity on individual particles will be measured by combining microelectrophoresis experiments, electrokinetic theory, and Monte Carlo simulations. The charge nonuniformity on particles will be related to the forces between particles. Using the recently-developed technique of "differential electrophoresis", the normal forces can be measured between two particles (those forces acting along the line of centers) and the tangential forces between them (those forces acting laterally along adjacent surfaces of the particles) with sub-piconewton resolution. Differential electrophoresis can measure interparticle forces between two Brownian particles at gaps less than 100 nanometers, where van der Waals forces are important.