Phase behavior of microemulsions based on food-grade nonionic surfactants: effect of polyols and short-chain alcohols

The improved water and oil solubilization in the presence of polyols (propylene glycol, PG, and glycerol, Gly) and short-chain alcohol (ethanol) in U-type nonionic W/O and O/W food microemulsions was investigated. The phase behavior of systems based on Tweens (ethoxylated sorbitan esters) was compared with non-food-grade systems based on C18:1E10 (Brij 96v). Short-chain alcohol (ethanol in food-grade systems) together with polyols (glycerol and propylene glycol) when added to a three component system (oil–surfactant–water) induce the formation of both water-in-oil (W/O) and oil-in-water (O/W) microemulsions. Alcohols and polyols destabilize the liquid crystalline phase and extend the isotropic region to higher surfactant concentrations. The total monophasic area, AT, at R(+)-limonene/ethanol of 1/1 (w/w) and aqueous phase of water/PG of 1/1 (w/w), was 73 and 64% of the total area of the phase diagram for Brij 96v and Tween 60, respectively. The transition from a W/O microemulsion into an O/W microemulsion happens gradually, and continuously without any phase separation. The total monophasic area depends also on the type of the oil, on the composition of the polar and apolar phases, and on the nature of the polyol. The results are discussed in terms of BSO equation, spontaneous curvature, H0, film flexibility, κ and κ̄, surfactant oil and surfactant cosolvent compatibility and the participation of the polyol at the interface. The difference in temperature sensitivity of PG-based microemulsions vs. temperature sensitivity of Gly-based is demonstrated and explained.