Molecular Simulation of Volume Phase Transition in Polymer Gels

聚合物凝胶通常用于工业、分析和家庭应用。 越来越多地，正在研究具有新化学和结构的凝胶，不仅用于改善已知工艺和产品的性能，而且用于开发用于化学和生物医学应用的新材料。 这些应用通常依赖于对凝胶溶胀行为的精确控制。 然而，由于缺乏对聚合物凝胶体积行为的物理基础的分子水平的理解，有用的凝胶的开发受到阻碍。 在这项工作中，我们建议发展必要的理论形式主义预测聚合物凝胶的相行为从分子考虑，使新的材料尚未被发现的性能可以设计在一个更合理的，科学的基础上，建议进行Monte Carlo模拟和半理论计算，研究几类聚合物凝胶体相变的分子基础。 特别是，主要研究者检查（i）熵因素（如网络拓扑结构，链刚度，链长不对称性）和（ii）能量相互作用（如疏水相互作用，离子力）对体积相变的发生和特征的影响。 到目前为止，溶胀只通过分子模拟研究了有限的一类规则的中性网络。本项目还将研究凝胶中的体积相变和其他流体-流体相变之间的关系。 为了有效地描述高度各向异性的相互作用（由于氢键或介晶基团）和可压缩性的凝胶的结构和热力学的影响，我们模拟粗粒度的分子模型在一个连续。 该方法需要从简单到复杂的聚合物凝胶，以及不同的系统，如弹性体和应变诱导弹性体的连续研究。 这种系统的复杂性，将需要开发新的蒙特卡罗模拟方法，能够捕捉他们的相行为。 这里提出的工作将提供数值数据来测试凝胶溶胀的几个理论的基本假设和预测。 更重要的是，它可以提供一般的指导方针，改进的聚合物凝胶的设计，充分利用熵力在多组分系统中占主导地位。关键词：材料、聚合物和凝胶

ABSTRACTCTS-9901430Juan de PabloPolymer gels are commonly used in industrial, analytical, and domestic applications. Increasingly, gels with novel chemistry and architecture are being investigated not only to improve the performance of known processes and products, but also to develop new materials for chemical and biomedical applications. These applications often rely on the precise control of the swelling behavior of a gel. Development of useful gels has been hampered, however, by the lack of a molecular-level understanding of the physics underlying the volumetric behavior polymer gels. In this work we propose to develop the necessary theoretical formalism to predict the phase behavior of polymer gels from molecular considerations, so that new materials with yet to be discovered properties can be designed on a more rational, scientific basis.It is proposed to perform Monte Carlo simulations and semi-theoretical calculations to study the molecular basis of several classes of volume phase transitions in polymeric gels. In particular, the principal investigator examine the effect of (i) entropic factors (such as network topology, chain stiffness, chain length asymmetry, and (ii) energetic interactions (such as hydrophobic interactions, ionic forces) on the onset and characteristics of volume phase transitions. To date, swelling has only been investigated by molecular simulation for a limited class of regular, neutral networks.This project will also investigate the relation between volume phase transitions in gels and other fluid-fluid phase transitions. In order to describe effectively the effect of highly anisotropic interactions (due to hydrogen-bonding or mesogenic groups) and compressibility on the structure and thermodynamics of the gel, we simulate coarse-grained molecular models in a continuum. The approach entails a sequential study from simple to complex polymeric gels, and systems as diverse as polyelectrolyte gels and strain-induced nematic elastomers. The complexity of such systems will require that novel Monte Carlo simulation methods be developed capable of capturing their phase behavior. The work proposed here will provide numerical data to test basic assumptions and Predictions of several theories for gel swelling. More importantly, it could provide general guidelines for the design of improved polymeric gels, which take full advantages of the entropic forces prevailing in multicomponent systems. Key words: materials, polymers and gel