Study on Non-equilibrium Interface Phenomena by Doppler Rippbn Spectroscopy

点击翻译按钮获取中文摘要

Langmuir films attract a great physical and industrial interest as a two-dimensional material adsorbed on the liquid surface and liquid-liquid interfaces. The observation of the film structure and the dynamic process of the molecular association is, however, very much difficult since they has the thickness of only one molecular length. The purpose of the study was directed to the development of a novel measurement system of the liquid surface dynamics related to the molecular adsorption/desorption processes. We first demonstrated the possibility of measuring the ripplon power spectrum of the flowing surface by applying the light scattering system to the surface flow cell We successfully observed the asymmetric ripplon spectrum, which is attributed to the flow of the surface; the ripplon propagating along the flow has larger phase velocity than that propagating against it. The asymmetry gives the surface velocity and then it leads to the age of the surface. The dynamic surface process was actually observed for the aqueous solution of the octanoic acid and sodium myristic acid and we found that the surface tension decreases with the aging of the surface. The typical time constants of the surface relaxation are obtained to about several hundreds of ms, which agree well with the theoretical prediction based on the molecular diffusion phenomenon. Further, we tried to obtain the ripplon spectrum within only 10 ms by applying the digital accumulation and the signal processing system for the random signal of te incoherent thermal ripplon. The time resolution of the new system is the world record of the surface measurement at present. The system also provides the surface visco-elasticity besides the surface tension and would give useful information on the condensation of the monomolecular films. The technique would be a powerful and standard tool to investigate the liquid surface physics.