Phase Inversion Characteristics Observed upon Water Dilution of a Bidiscontinuous Phase

This study presents a directly aggregated pseudo-ternary system. The three apexes of the investigated system represent a surfactant phase [Tween 80:propylene glycol (9:1 wt ratio)], an oil phase [isopropyl myristate:benzyl alcohol (7.5:2.5 wt ratio)], and water. Within the pseudo-ternary system, water dilution line, termed N91 (90 wt% surfactant phase and 10 wt% oil phase), was found to represent transparent and thermodynamically stable compositions from concentrate to high water dilution (>95 wt% water). Despite that the system was found to be directly aggregated, dilution line N91 exhibited classical L2→L1 phase inversion characteristics (at 39 wt% water). To explain this phenomenon, a novel structural interpretation regarding the observed inversion as an obstruction of the bidiscontinuous phase, consisting of oil and water-segregated domains, is proposed. The evaluation of dilution line N91 was based on electrical conductivity, SAXS, SD-NMR, rheometry, DSC and cryo-TEM.