Quartz resonator-based approach to ultrasonic rheology of a mixed-phase micellar system

We report the application of a quartz crystal microbalance with dissipation monitoring (QCM-D) to rheology of mixed-phase micellar systems. This novel application of QCM-D allows for the facile monitoring of complex systems under a variety of conditions. Viscosity measurements were obtained for sodium dodecyl sulfate (SDS) solutions, ranging from 1.0 to 50.0 mg/mL, in the presence and absence of toluene. Toluene was shown to swell SDS micelles as observed through an increase in viscosity, and an inflection point designating the critical micelle concentration (CMC) was clearly visible. Aqueous SDS solutions were also stabilized with sodium chloride (NaCl), up to 1.2 M, and with n-dodecanol in toluene solutions, up to 5.0 vol %. Rodlike micelle formation and swelling with toluene were observed in both cases, supporting previous studies. These studies show that a QCM-D approach to ultrasonic rheology holds potential for the specific study of multiphase systems, non-Newtonian fluids, and low volumes of analyte, aspects highly useful for complex or expensive colloidal dispersions such as micellar or biomolecular solutions.