ABSTRACT
This chapter is concerned with nonaqueous foams that require, for formation and stabilization, a surface-active solute. Generally pure, low-viscosity liquids do not yield persistent foams; however, highly viscous fluids such as melted organic polymers do yield stable foams. There are differences between aqueous and nonaqueous foams, ideally the same basic theories should apply to both types. The surface tension of a liquid typically decreases as the concentration of a surfactant is increased. Concentration of certain surface-active solutes at the liquid—gas interface results in rheological properties different from the bulk liquid. The chapter discusses the present understanding of the processes for producing solid foams. The chemistry of these foams is based on the catalyzed reaction of an isocyanate with an active hydrogen-containing material such as alcohols, amines, and water. The structure of a foam is composed of lamellar films joined together to form distorted polyhedral shaped cells.
