Colloid Polym Sci 274:81-84 (1996) Steinkopff Verlag 1996 J. L. Salager M. Perez-Sanchez Y. Garcia Physicochemical parameters influencing the emulsion drop size Received: 18 November 1994 Accepted: 8 August 1995 Prof. Dr. J.-L. Salager ( ~ ) M. Perez-Sanchez Y. Garcia Lab. FIRP Ingenieria Qu~mica Universidad de Los Andes M6rida 5101, Venezuela Abstract The stirring-mixing energy is the most obvious factor in the drop size reduction process, but it is not necessarily the most important one. Both the physicochemical formulation and the composition variables are shown to play a determinant role, at constant stirring condition. The generalized formulation versus water/oil ratio diagram allows to map emulsion properties such as emulsion type, stability and viscosity. It is used to discuss the combined effect of the formulation and composition upon the emulsion drop size, through their influences on the interfacial tension, and the emulsion viscosity and stability. Key words Emulsion - drop size - bimodal - distribution Introduction The emulsion type and other properties have been shown to depend upon the physicochemical formulation, i.e., surfactant type, oil nature, brine electrolyte content, temperature etc, as well as the composition variables, i.e., the water/oil ratio and the surfactant concentration, and mechanical mixing conditions (1-2). When the effects of all formulation variables are gathered in the so-called generalized formulation, the phenomenology can be represented on a formulation- water/oil ratio map that has been used by us and other research groups (3-8). Figure 1 illustrates the main fea- tures of such a map. The shaded zone corresponds to the three-phase behavior at or near optimum formulation. The formulation variable scale is such that the hydro- philicity increases from top to bottom. Above (respectively below) the three-phase behavior region, a Winsor II or (respectively Winsor I or 2) phase behavior occurs (9-10). The symbols indicate a two-phase behavior in which the surfactant rich phase is the upper phase, i.e. the oil phase (2) or the lower phase, i.e., the water phase (2), depending upon the top or bottom position of the mnemotechnical bar. As far as the emulsion type is concerned, the measure- ment of the electrolytic conductivity allows to determine the high (O/W) and low (W/O) conductivity emulsions, and to draw the inversion line (bold line in Fig. 1) as the boundary between the associated regions. As shown in Fig. 1, the map can be divided into three vertical regions, labeled A, B and C, with the + or - superscript, depending on the position with respect to the optimum formulation (3). In the central region (A), the emulsion type is asso- ciated with the phase behavior, while the extreme (B) and (C) regions exhibit an emulsion type in which the external phase is the one in higher proportion. Typically the A region extension ranges from 25 to 75% water or oil. Emulsions produced by stirring equilibrated systems whose formulation-composition is located in the A + (and B +) regions, as well as A- (and C-) regions have been called normal emulsions. They are stable, whenever their formulation is not too close from optimum formulation.