Optical tweezers have been used to investigate the dependance of electrostatic inter-particle forces on separation, in systems consisting of pairs of either model silica beads or emulsion droplets. Measurements were carried out as a function of ionic strength and, at salt concentrations where the Debye length was larger than the standard deviation of Brownian fluctuations of the particles in the traps, results were found to agree reasonably well with the predictions of DLVO theory. Experiments were also carried out where the salt concentration of the environment was changed in real-time while interactions were continuously measured. Specifically, single pairs of particles or emulsion droplets were held in a microfluidic channel in close proximity to an interface created between milliQ water and a 5 mM NaCl solution. Changes in the force-separation curves were measured as a function of time and used to monitor changes in the Debye length, and thus the local salt concentration, as ions diffused away from the interface. The results were shown to be consistent with expectations based on a relevant diffusion equation.
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机译：在由成对的模型二氧化硅小珠或乳化液滴组成的系统中，光镊已用于研究静电粒子间力对分离的依赖性。测量是离子强度的函数，在盐浓度下，德拜长度大于阱中颗粒的布朗波动的标准偏差，发现结果与DLVO理论的预测相当吻合。还进行了实验，其中环境的盐浓度实时变化，同时不断测量相互作用。具体而言，将单对颗粒或乳剂液滴保持在微流体通道中，该通道非常靠近milliQ水和5 mM NaCl溶液之间产生的界面。力-分离曲线的变化作为时间的函数进行测量，并用于监测德比长度的变化，从而监测离子从界面扩散开来时盐浓度的变化。结果表明与基于相关扩散方程的预期一致。
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