2022 年 67 巻 1 号 p. 22-28
“Rheology”is very useful in the development of cosmetics. Rheological measurement is effective in obtaining quantitative and reproducible results, although the sensory evaluation is the mainstream method for evaluating the usability of cosmetics. The feeling of the cream correlates with its viscosity at a shear rate of 103 s−1, which can be measured with a commercial rheometer. To obtain a better correspondence, it was found to be effective to measure the viscosity in the high shear rate range (104-105 s−1) by narrowing the gap between samples. The viscosity of α-gel, a base material for cosmetics, showed a two-step change with aging, and the frequency sweep indicated the existence of two relaxation mechanisms. It was suggested that these changes corresponded to the multi-lamellar vesicle and the lamellar structure, which undergo the phase transition with aging. We performed to visualize the change in internal structure under shear flow by Rheo-SALS measurement. In some samples, the internal structure was elongated (oriented) in the flow direction with applied shearing, suggesting that it may be necessary to consider the structural recovery and stability. Rheo-optic measurements such as Rheo-SALS can be used to evaluate the formation of millimeter-sized structures based on the molecular orientation induced by shear flow, and thus can be expected to be used for the above-mentioned studies in the future.
