Increased Ordering of Potassium Stearate/Stearic Acid/Glyceryl Stearate Confined between Swollen Cross-Linked Poly(acrylic acid)

In this paper, we investigate the phase behavior of a surfactant mixture comprising glyceryl stearate, potassium stearate, and stearic acid, in the presence of Carbopol, a commonly used thickener in personal care products. At low Carbopol concentrations (<0.03%), the surfactant mixture interacted with Carbopol electrostatically, increasing the degree of Carbopol swelling and, consequently, the overall viscosity. However, such an effect diminished as the Carbopol concentration was further increased. At a Carbopol concentration of 0.2%, two types of liquid crystalline surfactant structures, namely, multilamellar vesicles and lamellae, were observed between the swollen Carbopol domains. Although similar types of surfactant structures were present in a much more concentrated surfactant solution having a similar viscosity but without Carbopol, the lamellae in the presence of Carbopol were more ordered and with a larger d spacing. The increased ordering was probably induced by the interactions between the surfactants and Carbopol as the surfactants were confined between the swollen Carbopol domains.