Study on the development of wax emulsion with liquid crystal structure and its moisturizing and frictional interactions with skin.

The moisturizing and frictional interactions between emulsion and skin have a significant influence on the moisturizing efficacy and sensory properties of cosmetics. To deeply understand the interactions, we developed a kind of wax emulsion with liquid crystal structure and studied their interactions with dry, semi-moist and fully-moist skin. The moisturizing interaction was studied by using skin hydration test and tape stripping analysis, and it was found that with the increasing of liquid crystal content in the emulsion, the skin hydration level increased, desquamation index decreased and number of cutaneous lines increased, suggesting the increased moisturizing effect and barrier function. The frictional interaction was studied by finger friction test, and it was found that firstly during and after the application of emulsion on skin, the frictional interaction followed the stribeck-curve rule of lubrication. Secondly, when changing the water content of the substrate skin, the frictional behavior of the whole system showed a bell-curve behavior. Both skin hydration and water amount in the interfacial film played role in the frictional interaction between emulsion and skin, and the frictional interaction mechanism between wax emulsion and finger skin with different type of skin was proposed. This was the first time to study and discuss the effect of skin moist status on the moisturizing and frictional interactions between cosmetic emulsion and skin. The findings were significant for the design of high quality personal care products.