Phase behavior and rheology of mixed systems of potassium cocoyl glycinate and fatty acid salts

Abstract

The phase behaviors of mixed systems comprising the amino acid surfactant potassium cocoyl glycinate (PCG) and soap-based surfactants, including potassium laurate (PL), potassium myristate (PM), potassium palmitate (PP), and potassium stearate (PS), were systematically investigated. The concentrations of the transition from spherical to rod-like micelles of the mixed system were determined using conductivity. The phase transition temperatures were determined using differential scanning calorimetry (DSC). The liquid crystal phases formed in the region of high surfactant concentration were initially investigated using polarized optical microscopy (POM), and the types of liquid crystal phases were further characterized using small-angle X-ray scattering (SAXS). Finally, the rheological behavior of different phase states was studied by varying the concentration and temperature. The results show that the mixed systems of PCG and soaps exhibit rich phase behavior, and the liquid crystal phases exhibit hexagonal and lamellar phase liquid crystals. The type of soap and the compounding ratio both affect phase behavior, specifically in terms of the extent of the phase region. Furthermore, the rheological properties of the sample are associated with the self-assembled structure of the surfactant. This study provides a reference for the application of the mixtures of amino acid surfactants and soaps in detergents and cosmetics.