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

近年来，在液固界面附近形成的各种奇异的分子缔合微结构引起了物理和工业领域的极大兴趣。我们发展了一种新的技术--动态倏逝光散射技术，用于研究固液界面附近液体物质的结构和动力学。动态光散射测量是通过热涨落激发的热扩散、声子和布朗运动来研究液体中分子动力学的一种有效方法。倏逝光是在全反射条件下在界面附近产生的泄漏光波。由于倏逝光的穿透长度在几十nm的量级，因此它将是拾取近界面区域信息的有效探针。本研究的目的是建立动态倏逝光散射方法作为研究软材料界面物理的有力工具。从微观角度研究了界面与分子或分子缔合物之间的物理相互作用，并成功地研制了两种不同的光散射测量系统，一种是倏逝光散射系统，另一种是受抑倏逝光散射系统。这两种方法在原理上是不同的，并且在界面区域的动力学上提供了互补的信息。我们揭示了微粒的扩散行为，这是由来自固体壁的流体动力学相互作用抑制。用考虑水动力效应的脉动耗散理论对实验结果进行了较好的解释。消逝光散射将为研究软质复杂材料界面附近的奇异结构提供有力的工具。

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.