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。非均匀电荷分布将显著改变粒子间力。研究目标是：在单个微米大小的胶体粒子上测量纳米尺度的电荷不均匀性；胶体颗粒上电荷的不均匀性与所测的粒子间的法向和切向胶体力有关。这项研究部分是由PI最近的数据推动的，该数据显示，两个不接触的粒子之间的切向胶体力与时间有关，这可能是由于电荷分布不均匀造成的。电荷不均匀性对体悬浮稳定性和流变性的建模有重要影响。结合微电泳实验、电动力学理论和蒙特卡罗模拟，对单个粒子的电荷不均匀性进行了测量。粒子上电荷的不均匀性与粒子间的作用力有关。利用最近发展的“差示电泳”技术，可以以亚皮牛顿的分辨率测量两个粒子之间的法向力（沿中心线作用的力）和它们之间的切向力（沿粒子相邻表面横向作用的力）。差示电泳可以测量两个布朗粒子之间小于100纳米间隙的粒子间力，其中范德华力是重要的。

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.