Phase behavior of C18 monoglyceride in hydrophobic solutions

TL;DR

This study investigates the phase behavior of C18 monoglycerides in oil, revealing unique phase structures and transitions influenced by concentration, temperature, and hydration, with implications for understanding surfactant systems in non-aqueous environments.

Contribution

It provides new insights into the phase structures of MG in oil, including the identification of inverse lamellar and crystalline phases, and the effects of hydration on these phases.

Findings

Identification of inverse lamellar and crystalline phases in MG/oil systems

Hydration alters phase behavior and structure

Rheology confirms gelation during cooling

Abstract

We apply a set of different techniques to analyze the physical properties and phase transitions of monoglycerides (MG) in oil. In contrast to many studies of MG in water or aqueous systems, we find a significant difference in the phase structure at different concentrations and temperatures. By adding small quantities of water to our base MG/oil systems we test the effect of hydration of surfactant head-groups, and its effect on the phase behavior. The phase diagrams are determined by calorimetry and their universal features are recorded under different conditions. Two ordered phases are reported: the inverse lamellar gel phase and the sub-alpha crystalline gel phase. This sequence is very different from the structures in MG/water; its most striking feature is the establishing of a 2D densely packed hexagonal order of glycerol heads in the middle of inverse lamellar bilayers. Rheology was examined through temperature scans to demonstrate the gelation phenomenon, which starts from the onset of the lamellar phase during the cooling/ordering process.