Research Initiation Award - Microscopic Study of the Phase Behaviour of Liquid Crystalline Polymers

计算机模拟算法和液态理论的最新进展使柔性聚合物熔体和溶液的微观研究成为可能。本研究的目的是将这些方法扩展到液晶聚合物的研究中。利用计算机模拟和密度泛函理论，寻求对这些系统的相行为的基本理解，从而帮助特定应用的新聚合物工程。蒙特卡罗模拟密集熔体的聚合物将首先使用一个简单的半柔性链模型，然后更现实的旋转异构状态模型。这些模拟将用于测试近似理论，并在必要时提出新的近似。我们将研究几种理论方法。这将包括一个具有重整化自一致分子间势的Onsager理论，以及一个具有多余自由能泛函的密度泛函理论，该泛函是通过将全柔性聚合物熔体的广义Flory理论扩展到向列流体而得到的。提出的研究有几个方面。(i)将在研究近似理论的同时进行大规模计算机模拟，从而使两者之间有相当大的联系。（ii）理论中一些最困难的方面将通过简单的双分子计算机模拟精确地执行。将发展同样适用于热致性和溶致性液晶聚合物的理论技术。将研究化学上真实的模型，以便与没有可调参数的实验进行比较。如果成功，这些理论将为新材料的设计提供依据化学结构预测平衡性质的方法。我们提出的工作可能存在的缺点是，我们希望开发的技术可能被证明对工业上的常规应用来说计算量太大。即便如此，我们将对液晶聚合物的行为获得有价值的见解，这将有助于新材料的设计。

ABSTRACT CTS-9409856 University of Wisconsin Madison P.I.: Arun Yethirajo Recent advances in computer simulation algorithms and liquid state theory have made possible a microscopic study of flexible polymer melts and solutions. The purpose of the proposed work is to extend these methods to the study of liquid crystalline polymers. Using computer simulation and density functional theory, a fundamental understanding of the phase behavior of these systems is sought, thus assisting the engineering of new polymers for specific applications. Monte Carlo simulations of dense melts of polymers will be performed using first a simple semiflexible chain model and then more realistic rotational isomeric state models. These simulations will be used to test the approximate theories and suggest new approximations if necessary. Several theoretical approaches will be investigated. These will include an Onsager theory with a renormalized self-consistent intermolecular potential, and a density functional theory with an excess free energy functional obtained via an extension of the generalized Flory theory of fully flexible polymer melts to nematic fluids. There are several aspects to the proposed research. (i) Large scale computer simulations will be performed in conjunction with the investigation of approximate theories thus allowing for considerable interfacing between the two. (ii) Some of the most difficult aspects of the theories will be performed exactly via simple two molecule computer simulations. (iii) Theoretical techniques will be developed that are equally applicable to both thermotropic and lyotropic liquid crystalline polymers. (iv) Chemically realistic models will be investigated which will facilitate comparison with experiment without adjustable parameters. If successful, the theories could be useful for the design of new materials by providing means of predicting the equilibrium properties from the chemical structure. The possible disadvantage of our pr oposed work is that the techniques we hope to develop might prove to be too computationally intensive for routine use in industry. Even so, we will have obtained valuable insight into the behavior of liquid crystalline polymers that should assist the design of new materials.