Permanence and Stability of Emulsion Systems

Abstract

THE terms 'permanence' and 'stability' have often been regarded as synonymous when applied to emulsion systems. Until recently, neither term had a sufficiently rigid significance. In 1939, King and Mukherjee¹ defined the stability of an emulsion system as the reciprocal of the rate of change (with respect to time) of interfacial area, per unit area of initial emulsion interface. In this connexion the term 'specific interfacial area' ('specific surface', 'specific interface') may be expressed as being the number of square decimetres of interfacial area per gram of the dispersed liquid. These authors assumed that the rate of change of specific surface of an oil–water emulsion is proportional to the initial specific surface (although in later work² they found that there appeared, in some cases, to be two rates, an initial rapid change, followed by a slower change), that is, according to the simpler assumption, where s is specific surface; s₁ is initial specific surface; t is time; k₁ is instability factor; k is stability factor.