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.

Interfacial Behavior of Mixed Systems of Glycerylether-Modified Silicone and Polyoxyethylene-Modified Silicone.

Undecylglycerylether-modified silicone (GES; the glycerylether-type surfactant with a silicone segment and alkyl chains (carbon number, 11) as the hydrophobic portion) forms a molecular aggregate (M.A.) with a small amount of water. This M.A. is similar to the reversed hexagonal liquid crystal formed by alpha-mono long-chain alkylglycerylether (3-isooctadecyloxy-1,2-propanediol; GE). From the investigation of the phase behavior in the water/GES/polydimethylsiloxane (PDMS) ternary system, a wide three-phase region of water (W)+M.A.+oil (O) was observed. As this M.A. is insoluble in PDMS and easily orients in the interface between water and PDMS, the high water content silicone W/O emulsion using GES as a surfactant is well stabilized. However, as the PDMS content increased this W/O emulsion became less stable. In order to improve this stability, mixtures of GES and polyoxyethylene-modified silicone (PS) were applied to the silicone emulsion as co surfactant. By application of a PS with a methyl group at the end cap of the polyoxyethylene chain (PSM), the emulsion became most stable at a GES/PSM ratio of 1 : 2, and at the same time, the interfacial tension between the oil phase and the water phase became minimal. The reason for this was studied by the measurement of spin-lattice relaxation times (T(1)) of the alkyl chains of GES in the GES/PS/water system by (13)C NMR. We assumed that the W/O silicone emulsions were stabilized by the efficient orientation of the aggregates in the interface between the silicone phase and the water phase by using PSM as a cosurfactant. Copyright 2001 Academic Press.