ABSTRACT
This chapter reviews some simple rheological concepts and definitions. It presents several experimental configurations for measuring viscosity in the presence of wall slip, and reviews several techniques for measuring yield stresses. The chapter describes experimental results on the effects of volume fraction, dispersed phase size, and interfacial tension on foam and emulsion rheology. The effects of volume fraction span the range from “dilute” solutions of bubbles up to volume fractions approaching one. The dominant variables affecting rheology are the volume fraction of the bubble phase, the sizes of the bubbles, and the interfacial tension. Solid surfaces create a disturbance to the structure and local volume fraction of the dispersed phase for any multiphase system. A characteristic feature of cellular fluids at volume fractions of the dispersed phase above about 70 vol % is the existence of a yield stress. The measurement of the yield stresses of foams is complicated by the same issues that complicate the measurement of foam viscosity.
