Fast Dynamics of Inverse Wormlike Micelles Probed Using Mechanical and Dielectric Spectroscopy.

The rheology of wormlike micelle (WLM) solutions is tunable by engineering the micellar structure and topology. While much is known about how microscopic properties influence the rheological characteristics, questions remain regarding the quantification of fast relaxation processes, including Rouse and rotational modes. These fast processes are challenging to access using mechanical spectroscopy as bending modes dominate high-frequency mechanical measurements. In this work, we demonstrate the use of dielectric spectroscopy (DES) to directly interrogate these fast relaxation modes in solutions containing reverse WLMs. These consist of lecithin solutions in n-decane swollen with water. We develop an equivalent circuit model that separates the fast spectral features from the low-frequency processes and show that this relaxation feature is consistent with a combination of high-frequency Rouse and rotational modes. Further, we show that the low-frequency response is not determined by polymer dynamics alone. These findings demonstrate the potential of DES measurements to describe WLM behavior and pave the way toward in situ measurements under steady and transient shear flow.