Structural characterization of five-component food grade oil-in-water nonionic microemulsions

Abstract

The microstructure of a multi-component oil-in-water (O/W) microemulsion, to serve as a microreactor or a solubilization vehicle for food applications, has been studied using small angle scattering X-rays (SAXS) and neutron (SANS) techniques. Significant structural changes along selected aqueous dilution lines in the O/W microemulsions were determined. We found that the droplets’ size is affected by increasing the water content, the oleic phase concentration and content (mixture of R(+)-limonene and ethanol), and the nature of the surfactant (Brij 96v and Tween 60). The micellar size increases with increasing the aqueous phase content in both, Brij 96v-based and Tween 60-based systems. Replacing Brij 96v by Tween 60 at constant weight leads to larger microemulsion droplets. The increase in the surfactant concentration of these systems, as expected, leads to smaller interaction radii and to higher values of the number particle density. Increasing ethanol content in the oleic phase (R(+)-limonene plus ethanol) decreases the effective volume fraction, and causes reduction in the micellar size at decreasing surfactant aggregation number as a result of its redistribution between the interfacial film and the continuous aqueous phase. The SANS investigations allowed a focus on the main effects of propylene glycol (PG) and ethanol (EtOH). Both hydrophilic molecules have similar tuning properties on the microstructure. Both decrease the droplet size, render them more globular, and increase the number of micelles. It was concluded from these results that both alcohols are partially incorporated into the interface (most of it stays in the aqueous phase). The only observed difference in the investigated samples was that upon replacing the aqueous phase partially with PG, the effective volume fractions of the dispersed phase was decreased, while it remained unchanged when it was partially replaced by EtOH. PG and EtOH seem to influence the microstructure independently.