Characterization of Powder Cosmetics Based on Friction Dynamics.

Frictional properties are one of the most important physical factors in the design of powder cosmetics. In this study, 21 powder cosmetics were applied to artificial skin, and their friction characteristics were evaluated using a sinusoidal motion friction evaluation system. Three friction profiles were observed that depended on the sliding velocity. Principal component analysis showed that the principal component (Z), which characterized the friction dynamics of powder cosmetics, included the static friction coefficient (µ s), the kinetic friction coefficient (µ k), the delay time (δ), and the viscosity coefficient (C). Furthermore, a cluster analysis on Z suggested that powder cosmetics can be classified into three groups according to their friction dynamics. These results may be helpful to understand the phenomena that occur during the application of powder cosmetics.

Characterization of Cosmetic Dispersions Based on Friction Dynamics.

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.

Recognition Mechanism of the "Sara-sara Feel" of Cosmetic Powders.

The Sara-sara feel, which means "a state in which things are not damp or sticky and feel dry," is a preferred tactile sensation when people touch human skin, hair, clothing, and cosmetics. In this study, the Sara-sara feel was evaluated for silicone powder, cellulose powder, hydrophobized sericite powder, and various mixes of these powders. It was found that the highest Sara-sara feel score was achieved by the silicone powder. A multiple regression analysis showed that the Sara-sara feel was strongly correlated with a slippery feel. The relationship between certain physical properties, e.g., particle size distribution, and the slippery feel was analyzed to demonstrate how the subjects felt the slippery feel. It was observed that as the friction coefficient µ k was reduced, most subjects strongly felt the slippery feel. This coefficient slightly decreased when the composition of spherical silicone powder increased, because the contact area between spherical particles is smaller than that between plate and amorphous particles.

Physical origin of a complicated tactile sensation: 'shittori feel'.

Shittori feel is defined as a texture that is moderately moisturized; however, many people experience 'shittori feel' when they touch a dry solid material containing little liquid. Here, shittori feel was evaluated for 12 materials. We found that the highest score of shittori feel was achieved by powders. Multiple regression analysis showed that shittori feel is a complex sense of moist and smooth feels. We analysed the relationship between the physical properties and the moist/smooth feels to show how subjects felt certain feels simultaneously. The moist and smooth feels are related to the surface roughness and friction characteristics of the materials. The moist and smooth feels can be perceived when the finger starts to move on the material surface and when the finger moves and rubs the material surface, respectively.