Direct measurement of surface forces due to charging of solids immersed in a nonpolar liquid
Direct measurement of surface forces due to charging of solids immersed in a nonpolar liquid
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DOI：
10.1021/la015657s
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发表时间：
2002-05-14
期刊：
影响因子：
3.9
通讯作者：
Horn, RG
中科院分区：
文献类型：
--
作者：
Briscoe, WH;Horn, RG
首次直接测量非极性液体中带电固体表面之间的长程力。使用表面力装置对阴离子表面活性剂二-2-乙基己基磺基琥珀酸钠（AOT）在正癸烷中的毫摩尔浓度溶液中的云母表面之间进行测量，该装置经过改进以提高其检测弱和长程力的灵敏度。修改包括磁性驱动系统、使用弱悬臂弹簧以及以垂直配置安装的设备，以及对干涉光学的详细考虑，以允许精确测量高达几微米的表面间距。结果显示，排斥力与基于模型的理论曲线很好地拟合，在该模型中，只有反离子进入计算，换句话说，在溶剂中不存在离子库的情况下。将理论与数据进行拟合，可以估计出类似于 1 mC/m(2) 的云母表面电荷密度。提出了该溶液中云母表面充电的机制，其中包括不可避免存在的微量水和吸附的 AOT 表面聚集体的作用。讨论了结果与先前观察到的非水溶剂中胶体电荷稳定性的相关性。
Direct measurements of a long-range force between charged solid surfaces in a nonpolar liquid are presented for the first time. Measurements were made between mica surfaces in solutions of the anionic surfactant sodium di-2-ethylhexylsulfosuccinate (AOT) at millimolar concentrations in n-decane using a surface force apparatus which has been modified to improve its sensitivity for detecting a weak and long-range force. Modifications include a magnetic drive system, the use of a weak cantilever spring with the apparatus mounted in a vertical configuration, and a detailed consideration of the interference optics to allow accurate measurements of surface separations up to several micrometers. The results show a repulsion that is well fitted by theoretical curves based on a model in which only counterions enter the calculation, in other words, in the absence of a reservoir of ions in the solvent. Fitting the theory to the data allows an estimate of the mica surface charge density of similar to1 mC/m(2). A mechanism for surface charging of mica in this solution is proposed, which includes a role for trace amounts of water that are inevitably present and adsorbed surface aggregates of AOT. The relevance of the results to previously observed charge stabilization of colloids in nonaqueous solvents is discussed.