Development of rapid ripplon spectroscopy and its application to liquid surface physics

点击翻译按钮获取中文摘要

The purpose of this study is to develop a new light scattering system to detect the ripplon propagation with the time resolution of 1 ms. Ripplon is a thermally excited surface tension wave, whose propagation gives information on the molecular dynamics on the liquid surface, such as the adsorption process of surfactants and the two-dimensional phase transition of Langmuir films.As the result of the study, we could remarkably improve the sensitivity of the detection by introducing the highly coherent laser as well as the refined optical heterodyne interferometer. The higher frequency limit of the measurement was increased up to 50 MHz for the ripplon on pure water, which is the geometric limit of the light scattering. The system was then applied for the rapid measurement of the ripplon, in which the optical beating signal due to the ripplon is detected and recorded by the digital oscilloscope with long memory and the correlation function of the random surface motion is calculated. The accuracy of the measurement during the data acquisition time of 1 ms is better than 1 % for ripplon frequency and 5 % for the damping.The system is then applied for the measurement of the dynamic adsorption process of the typical surface-active agents of sodium myristic acid and we could successfully observed the temporal change of the surface tension after the cleaning the surface. The behavior of the surface recovery is examined with the model of the molecular diffusion and we found that the surface energy potential also plays an important role to determine the time constant of the surface formation. We also observed the oscillatory phenomenon of surface potential.