用相干散射探针研究软物质动力学和生物学
Dynamics in Soft-Matter and Biology Studied by Coherent Scattering Probes
摘要：
中子和X射线是相干探针，它们的相干特性用于散射实验。只有相干散射探针才能阐明分子的集体运动。虽然晶体中的声子已经研究了半个世纪，但软物质和生物学中的集体分子运动研究是一个相当新但即将到来的领域。集体动力学通常决定材料的性质和相互作用，并且对于建立动力学-功能关系至关重要。我们回顾了中子和X射线的性质，并推导出相干和非相干散射的起源。以膜和蛋白质中的分子运动为例，讨论了相干动力学和非相干动力学之间的区别，以及如何在X射线和中子散射实验中获得局部和集体运动。散射探针的相干特性的匹配在软物质和生物学中可能变得重要，因为（1）丢失长程有序和（2）涉及大的长度尺度。它可能在系统中很重要，在这些系统中，波动的纳米结构域强烈地决定了材料的性质。非弹性散射可以提供无序系统中非常局部的结构信息。非弹性中子散射实验表明，在凝胶-流体相变的范围内，磷脂双层中存在短寿命的纳米级凝胶和流体域，这可能是临界行为的原因，并确定弹性性质。
英文摘要：
Neutrons and x-rays are coherent probes, and their coherent properties are used in scattering experiments. Only coherent scattering probes can elucidate collective molecular motions. While phonons in crystals were studied for half a century now, the study of collective molecular motions in soft-matter and biology is a rather new but upcoming field. Collective dynamics often determine material properties and interactions, and are crucial to establish dynamics-function relations. We review properties of neutrons and x-rays and derive the origin of coherent and incoherent scattering. Taking molecular motions in membranes and proteins as example, the difference between coherent and incoherent dynamics is discussed, and how local and collective motions can be accessed in x-ray and neutron scattering experiments. Matching of coherent properties of the scattering probe may become important in soft-matter and biology because of (1) the missing long ranged order and (2) the large length scales involved. It is likely to be important in systems, where fluctuating nanoscale domains strongly determine material properties. Inelastic scattering can provide very local structural information in disordered systems. Inelastic neutron scattering experiments point to a coexistence of short-lived nanoscale gel and fluid domains in phospholipid bilayers in the range of the gel-fluid phase transition, which may be responsible for critical behavior and determine elastic properties.
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