Molecular Simulation of Volume Phase Transition in Polymer Gels

胡安-9901430Juan de Pablo聚合物凝胶通常用于工业、分析和家庭应用。人们越来越多地研究具有新颖化学和结构的凝胶，不仅是为了改善已知工艺和产品的性能，而且还为了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的物理基础的分子水平的了解，有用凝胶的开发一直受到阻碍。在这项工作中，我们建议发展必要的理论公式来从分子角度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出性能尚未被发现的新材料。建议通过蒙特卡罗模拟和半理论计算来研究聚合物凝胶中几类体积相变的分子基础。特别是，主要研究人员考察了(I)熵因素(如网络拓扑、链刚度、链长度不对称)和(Ii)能量相互作用(如疏水相互作用、离子作用力)对体积相变的开始和特征的影响。到目前为止，溶胀只是通过分子模拟来研究一类有限的规则中性网络。本项目还将研究凝胶中的体积相变与其他流体-流体相变之间的关系。为了有效地描述高各向异性相互作用(由于氢键或介晶基团)和可压缩性对凝胶结构和热力学的影响，我们在连续介质中模拟了粗粒分子模型。这种方法需要从简单的聚合物凝胶到复杂的聚合物凝胶，以及从聚电解质凝胶到应变诱导向列型弹性体的各种系统的连续研究。这类体系的复杂性要求开发新的蒙特卡罗模拟方法来捕捉它们的相行为。本文提出的工作将为检验几种凝胶膨胀理论的基本假设和预测提供数值数据。更重要的是，它可以为改进的聚合物凝胶的设计提供通用的指导方针，这种凝胶充分利用了多组分体系中普遍存在的熵力。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