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怪的分子缔合微结构引起了物理界和工业界的极大兴趣。我们发展了一种新的动态消逝光散射谱技术来研究固液界面附近液体材料的结构和动力学。动态光散射测量是研究液体中分子动力学的一种有效手段，它通过热涨落激发的热扩散、声子和布朗运动的行为来研究分子动力学。渐逝光是在全反射条件下，在界面附近产生的泄漏光波。由于消逝光的穿透长度在几十nm量级，因此它将是一种有效的探测近界面信息的方法。本研究的目的是建立动态消逝光散射法作为研究软材料界面物理的有力工具。我们还从微观的角度研究了界面与分子或分子缔合的物理相互作用。作为研究的结果，我们成功地开发了两种不同的光散射测量系统：一种是消逝光散射系统，另一种是受阻消逝光散射系统。这两种方法在原理上是不同的，并提供了关于界面区域动力学的互补信息。揭示了微颗粒的扩散行为，这种扩散行为受到来自固壁的流体动力相互作用的抑制。用考虑水动力效应的涨落耗散理论对实验结果进行了较好的解释。逝去光散射将成为研究界面附近软复杂材料奇特结构的有力工具。

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.