The static friction response of non-glabrous skin as a function of surface energy and environmental conditions

The (local) environmental conditions have a significant effect on the interaction between skin and products. Plasticisation of the stratum corneum occurs at high humidity, causing this layer to soften and change its surface free energy. In this work we study the effects of the micro-climate on the frictional behaviour of skin in contact with materials with varying wettability. Friction measurements are performed under a range of micro-climate conditions using four different materials with a smooth surface finish. All measurements are performed twice on a single subject in order to minimise variation in skin properties. Results show that materials with a higher wettability show a larger increase in friction coefficient when exposed to warm, moist conditions. The friction force is modelled using the skin micro-relief, the elastic properties of the different skin layers, the surface chemistry of both skin and counter surface, and the environment, as input parameters.