Molecular Origin of “kyu-kyu” in Detergency: Interaction of Surfactants with Model Stratum Corneum Liposomes

In the context of dishwashing, the acoustic emissions derived by the physical contact of the human fingertip across a wet lubricated surface (or dish) are defined by the Japanese term, ‘kyu-kyu’. These ‘kyu-kyu’ or squeaking sounds, indicative of customer satisfaction of a cleaned surface, have their origin in a physical phenomenon known as stick-slip friction. We hypothesize that this stick-slip, facilitated by the presence of a detergent, is caused in part by disruption of the surfactant bilayer absorbed to the contacting surface as rinsing occurs. The friction force may be mediated by the presence of mixed micelles, polymer additives, soils and skin lipids. Here, continuing on previous work in collaboration with Procter & Gamble, we propose a small angle neutron scattering (SANS) study of model stratum corneum (SC) liposomes and their interactions with common surfactants, SDS and DDAO (dodecyldimethylamine oxide), which are analogues of the surfactants used in P&G formulation. The SC lipid system comprises equimolar mixtures of ceramide N-lignoceroyl-D-erythro-sphingosine (Cer24NS)/free fatty acid (FFA)/cholesterol (Chol). The results will complement our direct measurement of friction between skin-mimics and a contacting surface, mediated by mixed surfactant systems.