Phase diagrams and property of colloidal systems prepared with an alkyl polyglucoside surfactant and the essential oil of Melaleuca alternifolia (tea tree)

Abstract

BackgroundThe purpose of this study was to develop the colloidal formulation, based on microemulsions and hydrogels, of Melaleuca alternifolia oil (aka tea tree oil, TTO) using a sustainable and biocompatible alkyl polyglucoside (APG) surfactant, Glucopon 600 CSUP (G600), commonly formulated for personal-care and home-care products. MethodsThe pseudo-ternary phase diagram of TTO-mixed surfactant-water was established with the water titration method at 25 °C. The mixed surfactants were composed of G600 and propylene glycol (PPG) as a co-surfactant at G600/PPG = 1/1, 2/1 and 3/1 (m/m). Colloid samples of one phase were further characterized with rheological measurements and dynamic light scattering (DLS) at 25 °C. Significant findingsThe samples containing TTO/mixed surfactant = 1/9 (m/m) and water show single phase only. With increasing water contents, the aforesaid system changed from Newtonian to pseudo-plastic, reflecting the transition from micellar solution / microemulsion to hydrogel. Especially, the gel-like behavior was confirmed with the dynamic oscillatory measurements, in which storage moduli were always larger than loss moduli at any time and any frequency under a constant strain of 0.5 %. Microemulsions made of 1 wt% tea tree oil and 9 wt% mixed surfactants were stable for > 1 month as monitored by aggregate size by DLS.