Department of Chemical Engineering, University of Washington, Box 351750, Seattle, Washington 98195-1750, United States.
Langmuir. 2012 Feb 7;28(5):3032-6. doi: 10.1021/la204000t. Epub 2012 Jan 17.
This paper presents an investigation of the charging behavior of mineral oxide particles dispersed in apolar media. There are a growing number of applications that seek to use electrostatic effects in apolar media to control particle movement and improve aggregation stability. Progress is limited, however, by incomplete knowledge of the mechanism(s) of particle charging in these systems. It has been shown in a number of cases that the acid-base properties of both the particles and the surfactants used to stabilize charge play key roles. A mechanism for acid-base charging has previously been established for mineral oxides in aqueous systems, where the surface hydroxyl groups act as proton donors or receivers depending on the pH of the surrounding solution. In water, the pH at which the surface charge density is zero, i.e., the point of zero charge (PZC), can be used to characterize the acid-base nature of the mineral oxide particles. The current work explores the possible extension of this charging behavior to apolar systems, with the key difference that the surface hydroxyl groups of the mineral oxides react with the surfactant molecules instead of free ions in solution. The apolar charging behavior is explored by measuring the electrophoretic mobility of a series of mineral oxides dispersed in a solution of Isopar-L and AOT, a neutral surfactant in water. The electrophoretic mobility of the particles is found to scale quantitatively, with respect to both sign and magnitude, with their aqueous PZC value. This provides support for the theory of acid-base charging in apolar media and represents a method for predicting and controlling particle charge of mineral oxides dispersed in apolar media.
本文研究了分散在非极性介质中的氧化物颗粒的荷电行为。越来越多的应用试图利用非极性介质中的静电效应来控制颗粒运动并提高聚集稳定性。然而，由于对这些系统中颗粒荷电的机制了解不完整，进展受到限制。在许多情况下已经表明，颗粒和用于稳定电荷的表面活性剂的酸碱性质都起着关键作用。以前已经为水系统中的矿物氧化物建立了酸碱荷电机制，其中表面羟基基团根据周围溶液的 pH 值充当质子供体或受体。在水中，表面电荷密度为零的 pH 值，即零电荷点 (PZC)，可用于表征矿物氧化物颗粒的酸碱性质。目前的工作探讨了这种充电行为可能扩展到非极性系统，关键区别在于矿物氧化物的表面羟基基团与表面活性剂分子而不是溶液中的游离离子反应。通过测量一系列分散在异链烷烃和 AOT（水中的中性表面活性剂）溶液中的矿物氧化物的电泳迁移率来探索非极性充电行为。发现颗粒的电泳迁移率在符号和大小方面都与它们的水 PZC 值定量成比例。这为非极性介质中酸碱荷电理论提供了支持，并代表了一种预测和控制分散在非极性介质中的矿物氧化物颗粒电荷的方法。
