Acrylamide as cosurfactant and hydrotrope in the pseudoternary Span 80-Tween 85/isopar M/water emulsion/microemulsion forming system

The aim of this study was to investigate the effects of acrylamide on emulsification of the pseudoternary Span 80-Tween 85/isopar M/water system at 40 °C. It was revealed that acrylamide could act as a surface-active agent to decrease the isopar M/water interfacial tension, and as a hydrotrope to increase the aqueous solubility of Tween 85, and further remarkably influence the emulsification of the investigated pseudoternary Span 80-Tween 85/isopar M/water system. The surface-active role of acrylamide could reduce the minimal weight fraction of the mixture of Span 80 and Tween 85 in pseudoternary systems (XST) to form stable water-in-oil (W/O) emulsions when the weight fraction of acrylamide in the aqueous domain (XAM) is below 0.1; while its hydrotropic role at high XAM levels (>0.1) could drive more Tween 85 molecules to transfer into aqueous phase and slightly improved the minimal XST to form stable W/O emulsions, as compared to that of XAM at 0.1. Moreover, under a given XST, the mean diameter of the droplet size distribution of the W/O emulsion remarkably decreased with the increase in XAM; while the smaller droplets in the W/O emulsion systems at higher level of XAM still coalesced rapidly when the compositions of the emulsion was slightly above the visually determined boundary between non-emulsion and stable emulsion regions.