Addressing the non-ideality of an application relevant surfactant mixture within the hydrophilic–lipophilic-deviation concept

Abstract

In cleaning products, selecting the right surfactants for the specific soil or contamination is crucial. The hydrophilic–lipophilic deviation (HLD) concept serves as a useful formulation tool by describing the interactions between surfactants, oil and water. However, for mixtures of ionic and non-ionic surfactants, the HLD concept assumes ideal mixing behavior, which does not hold true. Therefore, interactions between different surfactants must be considered. This can be achieved by introducing the interaction term G_EX/RT. Evaluating this interaction term using a set of equilibrated surfactant/oil/water (SOW) systems under various conditions is both time-consuming and resource intensive. This work aims to demonstrate the rapid determination of this interaction term using the dynamic phase salinity inversion (DSPI) method. We determined the phase behavior of a ternary surfactant system, consisting of sodium dioctyl sulfosuccinate, alkyl polyglucoside, and fatty alcohol ethoxylate, through both equilibrated systems and the DSPI method. Differences between the theoretical HLD calculations and actual experiments allowed us to access interaction terms. To validate G_EX/RT obtained by DSPI, we employed net-average-curvature concept to model the interfacial tension under different conditions. Spinning drop measurements showed excellent agreement between theoretical and measured values, confirming the applicability of DSPI for determining interactions in this surfactant system.