Proximal Adsorption in Colloidal Systems

弗吉尼亚理工学院和州立大学的威廉·A·达克博士是由化学部物理化学项目资助的关于胶体体系中近端吸附的研究。他将在由二氧化硅颗粒和季铵盐表面活性剂组成的模型体系中，测量表面活性剂的吸附作为颗粒之间的分离(近端吸附)的函数。在颗粒作用力和稳定性分析中，通常假定表面活性剂在颗粒碰撞时不吸附或解吸。这可能会导致严重的错误。他的力-距离-吸附测量结果将被用来确定近端吸附对胶体力的影响。结果还将与Hall和Ash等人发展的热力学理论进行比较，并将使用自洽场计算来探索近端吸附背后的微观机制。他将使用相互作用驱动吸附的概念作为一种途径，以改进对表面活性剂和聚合物体系中胶体稳定性的理解。与传统的静电和统计力学计算方法相比，这种方法的优点是方法简单，力直接与最容易控制的实验参数有关：添加剂在溶液中的浓度。研究生和本科生将接受表面化学理论和实验方法的培训，并将参与开发一种新的测量近邻吸附的仪器。我们在日常生活中遇到的许多物体实际上都是由非常细的颗粒组成的。例如，砖、纸、衣服、中国、土壤、大多数食品、化妆品，甚至人类都是由小颗粒组成的。这些对象的物理属性(例如，刚度、流动性和可加工性)取决于粒子之间的力。创造新的和改进的产品的过程的一部分是操纵颗粒之间的力以获得所需的材料特性。实际上，这些新的性质是通过添加表面活性剂和聚合物来获得的，它们吸附在颗粒的表面。我们知道，这种吸附是通过颗粒之间的碰撞来修改的，但在大多数理论中没有考虑这种影响，因此通常用于制定产品的推理缺少一个关键步骤。这项研究的目的是测量、模拟和理解碰撞过程中吸附的变化。这应该会为预测材料的物理性质提供新的指导方针。

Dr. William A. Ducker of Virginia Polytechnic Institute and State University is funded for his research on proximal adsorption in colloidal systems by a grant in the Physical Chemistry program of the Chemistry Division. He will measure the adsorption of surfactants as a function of the separation between particles (the proximal adsorption) in a model system consisting of silica particles and quaternary ammonium surfactants. In the analysis of particle forces and stability, it is common to assume that surfactants do not adsorb or desorb when particles collide. This can lead to serious errors. His results of force-distance-adsorption measurements will be used to determine the effect of proximal adsorption on colloidal forces. The results will also be compared to the thermodynamic theory developed by Hall and by Ash et al., and the microscopic mechanism behind proximal adsorption will be explored using self-consistent field calculations. He will use the concept of interaction-driven adsorption as a route for improved understanding of colloidal stability in surfactant and polymer systems. The advantages of this approach over conventional electrostatic and statistical mechanical calculations are that the approach is simple, and the force is directly linked to the most easily controlled experimental parameter: the concentration of additive in solution. Graduate and undergraduate students will be trained in both theoretical and experimental approaches to surface chemistry, and will join in the development of a new apparatus for measuring proximal adsorption.Many of the objects that we encounter in everyday life actually consist of very fine particles. For example, bricks, paper, clothing, china, soil, most foods, cosmetics, and even humans are composed of small particles. The physical properties (e.g. stiffness, flow, and workability) of these objects depends on the forces between the particles. Part of the process of creating new and improved products is the manipulation of the forces between particles to obtain desirable material properties. In practice these new properties are obtained through the addition of surfactants and polymers, which adsorb to the surface of the particles. We know that this adsorption is modified by collisions between the particles, but this effect is not taken into account in most theories, and therefore the reasoning commonly employed in formulating products is missing a key step. The aim of this research is to measure, model, and understand the change in adsorption during a collision. This should provide new guidelines for predicting the physical properties of materials.