Effect of interfacial properties on the drop size distribution of high internal phase ratio emulsions

Interfacial properties of polyoxyethylene(2) oleyl ether and drop size dist ributions of emulsions prepared with this surfactant are investigated exper imentally in this work; 80, 88 and 94% (v) internal phase ratio W/O type em ulsions were prepared, where the aqueous phase was 1% sorbitol solution and the oil phase, a 1:1 v/v mixture of surfactant and paraffin oil. Experimen tal evidence indicated an interaction between the hydrocarbon chains of sur factant molecules and the solvent paraffin oil through van der Waals forces and between the ethoxylate groups and sorbitol, a polyalcohol, in the aque ous phase through hydrogen bonds, notably below the transition temperature. Continuous phase liquid present in the plateau borders was found to act as a reservoir of surface active agents, minimizing the effect of stretching of the film under shear. In cases where the amount of liquid hold up in pla teau borders is negligible, the drop size distributions were found to be ve ry sensitive to shearing rate. Interplay between the interfacial shear visc osity and the interfacial tension was found to control the rate of coalesce nce of drops less than 0.48 mum only in the case of 94% emulsions, correspo nding to maximum stretching of interfacial area. In other cases, interfacia l film stability seems to control the rate of coalescence. (C) 2001 Elsevie r Science B.V. All rights reserved.