Prediction of Tactile Sensory Attributes of Facial Moisturizers by Rheology and Tribology

Twenty-three commercial samples of facial moisturizers were tested using rheological and tribological measurements and further compared to sensorial attributes as rated by descriptive panels. The correlation between panel ratings and mechanical properties of these products were studied and reported herein. As the panel evaluation proceeds from initial appearance, pick-up and rub-out to residue attributes, the sample thickness decreases from the centimeter scale to the micrometer scale. It was found that with this decrease, the dominating mechanical properties shift from rheological to tribological. Appearance and pick-up attributes seem to be governed by bulk rheology, while rub-out attributes are in a transient regime where both rheology and tribology are relevant. Besides, residue attributes are actually represented by the tribology of films. It is interpreted as evidence that the relevant mechanical properties pertain to film thickness. This conclusion is confirmed by stepwise multivariate linear regression analysis, which allows for the top two predictors to emerge: instantaneous viscosity maximum from rheology and coefficient of friction at a slow sliding speed from tribology.