Study on Molecular Dynamics near Solid-Liquid Interface by Evanescent Light Scattering Spectroscopy

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Recently, various kinds of strange microstructures of molecular association formed near the liquid-solid interface attract great interests both in the physical and industrial fields. We developed a new technique of Dynamic Evanescent Light Scattering Spectroscopy to investigate the structure and dynamics of liquid materials in the vicinity of solid-liquid interface. Dynamic light scattering measurement has been an effective technique to study the molecular dynamics in liquids through the behavior of the thermal diffusion, phonons and Brownian motion excited by the thermal fluctuation. Evanescent light is the leaky optical wave generated in the vicinity of the interface at the total reflection condition. Since the penetration length of the evanescent light is in the order of several tens of nm, it would be an effective probe to pick up the information on the near-interface region. The purpose of this study is to establish the dynamic evanescent light scattering method as a powerful tool of investigating the interface physics of soft materials. We also aimed to study the physical interaction between the interface and molecules or molecular association from the microscopic viewpoint.As a result of the study we successfully developed two different light scattering measurement systems; one is the evanescent light scattering system and the other is the frustrated evanescent light scattering system. These two methods are different in their principles and give complementary information on the dynamics at the interface region. We revealed the diffusion behavior of the micro particles, which is suppressed by the hydrodynamic interaction from the solid wall. The experimental results ape well explained by the fluctuation dissipation the fluctuation dissipation theory taking the hydrodynamic effect into account. The Evanescent Light Scattering would be a powerful tool for the investigation of the strange structure of the soft complex materials near the interface.