Ripplon on high viscosity liquid.

A ripplon is a thermally excited capillary wave propagating on liquid surface. Propagation of the ripplon reflects surface mechanical properties such as surface tension and viscoelasticity of the liquid. An optical beating ripplon spectroscopy technique developed by us was applied mainly to the observation of various surface phenomena on a lowly viscous liquid surface in the frequency range from 1 kHz to several 10 MHz. In this study, we carried out a light scattering observation of the highly damped ripplon on the surface of the viscous liquid. The spectral peak width of the damped ripplon was smaller for the higher viscosity and the optical beating technique could resolve such a structure. A strict description of the dynamic structure factor of the ripplon was employed to fit the experimental power spectrum of overdamped ripplon to viscosity up to 1000 cS.