Rheology and Pinching Dynamics of Soapy Formulations

Commercial liquid hand soaps and body washes are rheologically complex fluids with additives that influence smell, color, viscosity, phase behavior, and overall consumer's sensory experience when dispensing or pumping onto the hand, body, or sponge. Most commercial hand soap dispersions are multicomponent fluids that contain wormlike micelles, and therefore, often exhibit shear banding and elastic instabilities. In this contribution, we characterize the shear rheology response of commercial hand soaps using torsional rheometry and characterize their pinching dynamics and extensional rheology using dripping-onto-substrate (DoS) rheometry protocols. To better understand the connection between rheological studies and consumer sensory experience, we complement these studies with stretched liquid bridge experiments carried using Cambridge Trimaster as well as a home-built device, and develop an understanding of stringiness and gloppiness.