Structure of Highly Disordered Chains in Polymers by Vibrational Spectroscopy

本研究是利用振动光谱对聚合物体系的构象无序进行研究。无序性在决定聚合物材料的性质方面起着重要的作用，这激发了许多旨在表征和理解其复杂性质的活动。振动光谱学对无序的适用范围受到严重限制，因为缺乏一种通用但实用的理论，可以用来提供无序链分子体系的构象统计与红外或拉曼光谱之间的定量关系。作者的工作导致了一个模型，该模型能够在无序链的结构和光谱之间建立一般关系。该模型基于无序链的振动具有有序链的一些长程相干性这一发现。对一个简单系统的初步结果表明，用该模型计算的红外谱带形状重现了观测到的红外谱带的主要特征。这一模型将进行修改，以使其适用范围更广。对于这个问题的第二种方法也将被寻求，其中无序链的系综的谱是通过对为每个组成构象计算的谱求和而数值产生的。以这种方式获得的光谱将被用来开发将光谱和无序联系起来的模型，并测试已提出的各种聚合物的构象模型。此外，振动光谱和其他可用的技术，包括非弹性中子散射，将被用于研究各种无序聚合物体系。将特别强调以非平衡状态存在的体系以及链单分子层、液晶和液晶聚合物。

This research is a study of conformation disorder in polymer systems by vibrational spectroscopy. Disorder plays an important role in determining the properties of polymeric materials, and this has stimulated much activity aimed at characterizing and understanding its complex nature. The range of applicability of vibrational spectroscopy to disorder has been seriously limited by the absence of a general, but practical, theory that can be used to provide quantitative relations between the conformational statistics and the infrared or Raman spectrum of a system of disordered chain molecules. Work by the authors has led to a model that enables general relations to be established between the structure and spectra of disordered chains. The model is based on the finding that the vibrations of disordered chains have some of the long-range coherence of ordered chains. Preliminary results on a simple system show that infrared band shapes calculated with this model reproduce the main features of those observed. This model will be modified to make it more widely applicable. A second approach to this problem will also be pursued in which the spectra of ensembles of disordered chains are generated numerically by summing the spectra computed for each constituent conformer. Spectra obtained in this way will be used to develop models that relate spectra and disorder, and to test conformational models that have been proposed for various polymers. In addition, vibrational spectroscopy and other available techniques, including inelastic neutron scattering, will be used to study a variety of disordered polymer systems. Special emphasis will be devoted to systems that exist in nonequilibrium states and to chain monolayers, liquid crystals, and liquid crystal polymers.