Molecular Simulation of Volume Phase Transition in Polymer Gels

高分子凝胶广泛用于工业、分析和家庭应用。越来越多的人正在研究具有新型化学和结构的凝胶，不仅可以提高已知工艺和产品的性能，还可以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膨胀行为的精确控制。然而，由于缺乏对聚合物凝胶体积行为背后的物理学的分子水平的理解，有用的凝胶的发展受到了阻碍。在这项工作中，我们建议发展必要的理论形式，从分子的角度来预测聚合物凝胶的相行为，以便在更合理、更科学的基础上设计尚未发现性能的新材料。提出了用蒙特卡罗模拟和半理论计算来研究聚合物凝胶中几种体积相变的分子基础。特别是，首席研究员研究了(i)熵因素（如网络拓扑，链刚度，链长不对称）和（ii）能量相互作用（如疏水相互作用，离子力）对体积相变的开始和特征的影响。迄今为止，仅对一类有限的规则中性网络进行了分子模拟研究。这个项目也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相互作用（由于氢键或介生基团）和可压缩性对凝胶结构和热力学的影响，我们模拟了连续体中的粗粒度分子模型。该方法需要从简单到复杂的聚合物凝胶的顺序研究，以及不同的系统，如聚电解质凝胶和应变诱导的向列弹性体。这种系统的复杂性将要求新的蒙特卡罗模拟方法的发展能够捕捉他们的相位行为。本文提出的工作将提供数值数据来检验几种凝胶膨胀理论的基本假设和预测。更重要的是，它可以为改进聚合物凝胶的设计提供一般指导，这些改进聚合物凝胶可以充分利用多组分体系中普遍存在的熵力。关键词：材料，聚合物，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