Proximal Adsorption in Colloidal Systems

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

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.