Friction Dynamics of Organogel-type Cosmetics

The friction characteristics of organogel-type cosmetics play a crucial role in texture improvement. In this study, we evaluated the friction behavior of 32 organogel-type cosmetics when they were applied to artificial skin utilizing a sinusoidal motion friction evaluation system. The principal component analysis on the friction parameters demonstrated that the principal components Z₁ and Z₂ incorporated the static friction coefficient μ_s, dynamic friction coefficient μ_k, delay time δ, and viscosity coefficient C. The cluster analysis on Z₁ and Z₂ classified these cosmetics into four different categories based on friction dynamics: Group 1 comprised 14 formulations containing hydrogenated polyisobutene (a low-polarity oil) and triethylhexanoin (a medium-polarity oil); Group 2 comprises cosmetics with high pigment content, hardness and friction coefficient; Group 3 comprises cosmetics with high viscosity response. and positive velocity dependence due to the presence of various paste-type oils; and Group 4, in which the friction coefficient decreases with the increasing acceleration at the onset of sliding, demonstrates a negative viscosity coefficient. These cosmetics contain medium- to high-polarity oils exemplified by diisostearyl malate and tri(caprylic/capric)glyceryl. The classification method based on friction parameters proposed in this study is useful for understanding the application texture of organogel-type cosmetics and designing improved formulations.