Frictional properties are one of the most important physical factors in the design of cosmetic dispersions in which solid particles are dispersed in a liquid. The effects of ingredients and formulations on frictional properties have been previously reported. In this study, the frictional properties of 33 cosmetic dispersions were evaluated using a sinusoidal motion friction evaluation system when applied on an artificial skin. A detailed analysis of the velocity dependence of the friction coefficient demonstrated that all cosmetic dispersions exhibited stable pattern and the friction behavior did not change during the round trip. We analyzed friction-based parameters by principal component analysis and demonstrated that the principal components Z 1 and Z 2 include the static friction coefficient μ s, kinetic friction coefficient μ k, delay time δ, and viscosity coefficient C, and that these factors are involved in characterizing friction dynamics. The cluster analysis on Z 1 and Z 2 suggested that these dispersions can be classified in three groups with respect to friction dynamics. These results can help understand the characteristics of cosmetics and control their function and utility.
Keywords: categorization; cluster analysis; dispersion; friction; liquid cosmetics; principal component analysis.