Evaluation of the hydrophile-lipophile balance (HLB) of nonionic surfactants. I. Multisurfactant systems

Abstract

Since the hydrophile-lipophile property of nonionic surfactant for a given system is just balanced in a three-phase region of a phase diagram which is a stack of three-phase triangles consisting of an aqueous, a surfactant, and an oil phase, we defined the hydrophile-lipophile balance (HLB) plane on which the three-phase triangle is positioned in the midst of the three-phase region. In a three-component system of nonionic surfactant/water/oil, the HLB plane is located at fixed temperature ( T HLB). Accordingly, the equation of the HLB plane is represented by T = T HLB in this system, and, hence, the phase inversion temperature of emulsion (PIT) is independent of a surfactant concentration. Correlation between T HLB and the Griffin's HLB number was investigated and a linear relationship between them was obtained. In a multisurfactant system, a set of the HLB planes exists in a temperature range between T HLB of the most hydrophilic surfactant and that of the most lipophilic surfactant. The equation of the plane is obtained by a geometrical calculation in a space of temperature and compositions, assuming that the equilibrium concentration of surfactant in the aqueous phase is negligible. The effect of the temperature, the oil/water ratio, the weight ratio between the surfactants, and the surfactant concentration on the phase behavior of a mixed surfactant system is explained very well by the equation. The correlation between the T HLB of the surfactant mixture and Griffin's HLB number is also substantiated.