Raudsepp Allan, A K Williams Martin, B Hall Simon
Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand.
MacDiarmid Institute for Advanced Material and Nanotechnology, Victoria University of Wellington, Wellington, New Zealand.
Eur Phys J E Soft Matter. 2016 Jul;39(7):70. doi: 10.1140/epje/i2016-16070-1. Epub 2016 Jul 22.
Measurements of the electrostatic force with separation between a fixed and an optically trapped colloidal particle are examined with experiment, simulation and analytical calculation. Non-Gaussian Brownian motion is observed in the position of the optically trapped particle when particles are close and traps weak. As a consequence of this motion, a simple least squares parameterization of direct force measurements, in which force is inferred from the displacement of an optically trapped particle as separation is gradually decreased, contains forces generated by the rectification of thermal fluctuations in addition to those originating directly from the electrostatic interaction between the particles. Thus, when particles are close and traps weak, simply fitting the measured direct force measurement to DLVO theory extracts parameters with modified meanings when compared to the original formulation. In such cases, however, physically meaningful DLVO parameters can be recovered by comparing the measured non-Gaussian statistics to those predicted by solutions to Smoluchowski's equation for diffusion in a potential.
通过实验、模拟和解析计算，研究了固定胶体颗粒与光学捕获胶体颗粒之间的静电力随间距的变化情况。当颗粒靠近且捕获较弱时，在光学捕获颗粒的位置观察到非高斯布朗运动。由于这种运动，在直接力测量的简单最小二乘参数化中，当间距逐渐减小时，从光学捕获颗粒的位移推断力，除了直接源于颗粒间静电相互作用的力之外，还包含由热涨落整流产生的力。因此，当颗粒靠近且捕获较弱时，与原始公式相比，将测量的直接力测量简单拟合到DLVO理论会提取出具有修正意义的参数。然而，在这种情况下，通过将测量的非高斯统计量与由Smoluchowski势扩散方程的解预测的统计量进行比较，可以恢复具有物理意义的DLVO参数。
