Dispersion relation of capillary waves on ionic liquids: Observation of the fast overdamped mode

Abstract

We measured the capillary wave spectra on the surface of ionic liquids using dynamic light scattering techniques. Empirical dispersion relations deduced from the time domain analysis clearly reveal the transition from oscillating to overdamped behavior with changing temperature and the wave vector. In particular, not only slow but also fast modes were observed in the overdamped regime. The empirical dispersion relations coincide with the theoretical dispersion relations deduced from the linearized Navier-Stokes equation when experimentally determined density, viscosity, and surface tension are assigned to the latter.