La viscoélasticité des milieux complexes et leurs interactions avec la peau

Foresee the sensation produced by multiphase materials like creams, gels or emulsions, as early as they are designed, is at stake for cosmetic industry, inter alia, as it considerably fosters innovation. This prediction implies the resort to new measurement devices which are effective enough to be able to characterize multi-physical and multi-scale interactions (between product components and with product environment). It also entails the identification of typical physical quantities linking the instrumental study with data extracted from sensory analysis based on expert panel. To reach those objectives, this thesis manuscript exposes the update of a microrheological experimental set-up using a thickness shear mode ultrasonic transducer (TSM) and which can embark a human skin explant maintained in survival conditions. Besides the retrieving, thanks to the TSM, of physical quantities representative of products intrinsic interactions, the ex vivo biosensor aims to study skin/product interactions, which are supposed to be the perceived sensations roots. Because the viscoelastic estimation is performed with conditions close to real-world ones, coupling measurements derived from both sensors should allow an organoleptic characterization more objective and less skewed than usual instrumented sensory analysis studies. A new viscoelastic model relying on fractional derivative calculus has been phrased into equations to process microrheological data. In addition to the model relevance for studying complex fluids (non-Newtonian), its ability to sum physical quantities over microscopic and mesoscopic scales permit to work with materials ranging from perfect fluids to strong gels, as well as tissues with similar structures like skin layers. With sensory analysis as a final perspective, the link between these characterizations and the macroscopic scale of human perception will be discussed to find the physical signatures of sensory descriptors.