Rheology 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. Surfactants are a main ingredient in all commercial hand soaps with concentrations high enough for the formation of wormlike micelles. They often exhibit shear banding properties and elastic instabilities that affect the flow behavior with different shear flows and extensional flows. In this contribution, we characterize the shear rheology response of commercial hand soaps and body washes using torsional rheometry and characterize the pinching dynamics and extensional rheology using dripping-onto-substrate rheometry protocols. In order to better understand the connection between rheological studies and consumer sensory experience and satisfaction, we are developing non-standard characterization approaches to rank and analyze such products.