Colloids

Abstract

A colloid is a finely dispersed material, having a high surface‐area‐to‐volume ratio. It is usually a solid particle, but it may be a liquid droplet or a gas bubble. The differences in composition, structure, and interactions between the surface atoms or molecules and those on the interior impart colloids with diverse physicochemical properties that generally deviate from those of both the constituent atoms or molecules and the macroscopic material. Many technological problems relate to the behavior of colloids, especially those dispersed in a liquid or gaseous fluid. Commercial examples include metals, magnetic powders, catalysts, ceramics, minerals, oil recovery, technical glasses, paints and pigments, polymers, pulp and paper, prepared foods, pharmaceuticals, fibers, detergents, and purified water. Natural and biological systems can also depend on the behavior of colloids, and soil science and plant nutrition, meteorology, hematology, membrane science, and medical technology furnish numerous examples. Thus the ubiquity and importance of colloids have made the ability to control their formation, destruction, or stabilization a critical problem, irrespective of whether the colloidal material is deemed desirable or undesirable. This article addresses the physical and chemical properties of colloidal materials, their widespread applications, and the hazards associated with finely dispersed particulates.