Dynamics of Phase Separation and Mesophase Phase Transition in Liquid Crystal and Rigid-Rod Polymer Mixtures

本提案涉及由液晶(LC)和液晶聚合物(LCP)组成的聚合物复合材料和电光材料。众所周知，聚合物分散液晶(PDLC)的电光性能在很大程度上取决于液晶区的形态和分散程度。本提案试图通过控制分散Lx结构域的形态来基本了解聚合物分散液晶的电光性能。重点是确定液晶/聚合物混合物的热力学相图对最终形态的作用，包括液晶分散和新出现的微区尺寸。由于大多数聚合物体系很难达到平衡状态，特别是在聚合诱导相分离(PIPS)中，相分离动力学和向列相有序之间的竞争将被研究。本文从实验和理论上阐述了(I)液晶和侧链液晶(或刚性棒状)聚合物的相变动力学和临界现象，(Ii)链刚性对含有侧链和主链液晶聚合物的二元向列型液晶中相分离动力学的影响，(Iii)近晶型液晶/聚合物共混物的中间相有序化动力学和相分离动力学之间的竞争，以及(Iv)含有刚性棒状聚合物的纳米复合材料的相图和相分离动力学。基于含时Ginzburg-Landau方程(TGDL-Model C)，考虑浓度和取向有序(液晶有序)参数的耦合，建立了液晶/聚合物混合物的中间相有序化和相分离的动力学模型。建议将各向同性混合的Flory-Huggins(FH)理论和向列相有序的Maier-Saupe(MS)自由能泛函(或近晶有序的Maier-Saupe-McMillan(MSM)理论)引入TDGL方程。将阐明与耦合的TDGL-模型C方程有关的所有参数的物理意义，并展示它们的预测能力。将与最近的实验观测结果相比较，分析图案形成的动力学。认识到微区形态的可能控制和对介晶相互作用的更好理解，拟议的研究将扩展到纳米复合材料。如果成功，提出的理论将缓解一些问题，如试验和错误方法，导致在制备PDLC薄膜时无法重现所需的磁区形态和低成品率。在这十年中，我们见证了平板显示器等基于液晶的光学器件的巨大增长。预计在新千年，对先进的有机和聚合物光电材料的需求将会增加。这一领域的平板显示器一直由远东国家主导，主要是日本。重要的是，美国通过在这项不断增长和前景看好的技术中进行开创性的基础研究来保持其竞争优势。拟议的液晶/聚合物复合材料的实验和理论工作将有助于通过基本的科学理解开发对美国工业至关重要的新光学器件。另外重要的一点是，所有的仿真程序都是用VC++编写的，可以在LCD投影仪的帮助下，以实时模式显示LC域形态的出现。这样的互动项目对课堂教学很有用，因此对美国未来科学家和工程师的培训应该大有裨益。这种新的教学方法与阿克伦大学获得卡内基教学学院地位的目标是一致的。

9903519KyuThe present proposal deals with polymer composites and electro-optical materials consisting of liquid crystals (LC) and liquid crystalline polymers (LCP). It is a well-known fact that the electro-optical performance of polymer dispersed liquid crystals (PDLC) critically depends on the morphology and dispersion of liquid crystal domains. The present proposal seeks basic understanding of the electro-optical performance of polymer dispersed liquid crystals via controlling the morphology of dispersed LX domains. Emphasis has been placed on determination of the role of thermodynamic phase diagrams of LC/polymer mixtures on the final morphology including the LC dispersion and the emerging domain size. Competition between the dynamics of phase separation and nematic ordering will be investigated as most polymer systems hardly attain an equilibrium state, particularly in the polymerization induced phase separation (PIPS). This proposal covers the experimental and theoretical elucidation of (i) dynamics of phase transitions and critical phenomena in liquid crystals and side-chain liquid crystalline (or rigid-rod) polymers, (ii) effects of chain rigidity on dynamics of phase separation in binary nematics containing side-chain and main-chain liquid crystalline polymers, (iii) competition between the kinetics of mesophase ordering and dynamics of phase separation in smectic LC/polymer blends driven by either thermal quenching or chemical reactions and (iv) phase diagrams and phase separation dynamics of nanocomposites containing rigid rod polymers. To demonstrate how the thermodynamic phase diagrams can guide the kinetic pathway for the emergence of LC domains, a kinetic model for mesophase ordering and phase separation in liquid crystal/polymer mixtures has been developed based on the time-dependent Ginzburg-Landau equation (TGDL - Model C) involving coupling between the concentration and orientational order (liquid crystal ordering) parameters. It is proposed to incorporate the Flory-Huggins (FH) theory for isotropic mixing and Maier-Saupe (MS) free energy functional for nematic ordering (or Maier-Saupe-McMillan (MSM) theory for smectic ordering) into the TDGL equation. The physical significance of all parameters pertaining to the coupled TDGL - Model C equations will be clarified and their predictive capabilities will be demonstrated. The dynamics of pattern formation will be analyzed in comparison with recent experimental observations. Recognizing the possible control of domain morphology and improved understanding of mesogenic interactions, the proposed study will be extended to nano-composites. If successful, the proposed theory would alleviate some of the problems such as the trial and error approach that leads to irreproducibility of the desired domain morphology and low yields in fabrication of PDLC films.During this decade we have witnessed an immense growth in liquid crystal based optical devices such as flat panel displays. The demand for advanced organic and polymeric electro-optical materials is expected to increase in the new millenium. This area of flat panel displays has been dominated by Far East countries, primarily Japan. It is important that the United States maintains its competitive edge through the pioneering basic research in this ever-growing and promising technology. The proposed experimental and theoretical works on liquid crystal/polymeric composites will contribute to the development of new optical devices crucial for US industries through basic scientific understanding. Another important point is that all simulation programs have been written in Visual C++ to display the emergence of LC domain morphology in live-mode with the aid of an LCD projector. Such interactive programs are useful for classroom teaching and thus should be highly beneficial in the training of future scientists and engineers in the US. This new methodology of teaching is in line with the goal of the University of Akron in attaining Carnegie Teaching Academy status.