Complex fluids are widely used in personal care products, where the bulk fluid is usually made of many components (non-ionic and ionic surfactants, long chain polymers, perfumes and sometimes nanoparticulates). These components form a fluid that is usually highly viscous. There are very few techniques that are capable of discerning both the interfacial adsorption and the bulk properties at the same time. One possible way to access these properties is to use a Quartz Crystal Microbalance (QCM). A modern QCM can measure both the frequency response and the energy lost (the dissipation) from a laterally vibrating quartz crystal [1]. The QCM is highly sensitive to both the bulk fluid properties [2] and to any adsorption that may take place at the QCM crystal surface [3] and is thus ideally suited to complex fluids adsorption. It is possible to monitor the changes in fluid response in real time such that the kinetics may be obtained. We will present data showing how the QCM responds to (a) non-adsorbing viscous fluids, (b) specifically adsorbing viscous fluids and (c) viscous micellar fluids that are not unlike the basis for many commercial products. These results are dependent on (a) the adsorption taking place and (b) whether slip is occurring at the crystal-fluid interface or not.

[1] Rodahl M. and Kasemo B., Rev. Sci. Instrum. 67 (9) 3238 (1996) [2] Kanazawa K.K. and Gordon J.D. II, Anal. Chim. Acta 175 99 (1985) [3] Webber G.B., et al., Farad. Discuss. 128 193 (2005)