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

[903519]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域的形态和色散。本提案寻求通过控制分散LX域的形态来基本理解聚合物分散液晶的电光性能。重点是确定LC/聚合物混合物的热力学相图对最终形貌的作用，包括LC分散和新出现的畴尺寸。由于大多数聚合物体系难以达到平衡状态，特别是在聚合诱导相分离（PIPS）中，相分离动力学和向列有序动力学之间的竞争将被研究。这一建议涵盖了(i)液晶和侧链液晶（或刚性棒）聚合物中的相变动力学和临界现象，（ii）链刚度对包含侧链和主链液晶聚合物的二元向列线相分离动力学的影响，(3)由热猝灭或化学反应驱动的半晶LC/聚合物共混物的中间相有序动力学和相分离动力学之间的竞争；(4)含有刚性棒聚合物的纳米复合材料的相图和相分离动力学。为了证明热力学相图如何指导LC域出现的动力学途径，基于时间相关的金兹堡-朗道方程（TGDL -模型C）建立了液晶/聚合物混合物中中间相有序和相分离的动力学模型，该模型涉及浓度和取向顺序（液晶有序）参数之间的耦合。提出将各向同性混合的flury - huggins （FH）理论和向列有序的Maier-Saupe （MS）自由能泛函数(或近序的Maier-Saupe- mcmillan （MSM）理论合并到TDGL方程中。将阐明与耦合TDGL - Model C方程有关的所有参数的物理意义，并证明它们的预测能力。图案形成的动力学将与最近的实验观察结果进行比较分析。认识到结构域形态的可能控制和对介生相互作用的改进理解，提出的研究将扩展到纳米复合材料。如果成功，所提出的理论将缓解一些问题，如试验和错误的方法，导致所需的区域形态的不可重复性和低产量的PDLC薄膜的制造。在这十年中，我们目睹了基于液晶的光学器件（如平板显示器）的巨大增长。预计在新千年，对先进有机和聚合物电光材料的需求将会增加。平板显示器的这一领域一直由远东国家主导，主要是日本。重要的是，美国通过在这一不断发展和有前途的技术上的开创性基础研究来保持其竞争优势。提出的关于液晶/聚合物复合材料的实验和理论工作将有助于通过基础科学理解开发对美国工业至关重要的新型光学器件。另一个重要的一点是，所有的模拟程序都是用Visual c++编写的，以便在LCD投影仪的帮助下在实时模式下显示LC域形态的出现。这样的互动项目对课堂教学是有益的，因此对美国培养未来的科学家和工程师是非常有益的。这种新的教学方法符合阿克伦大学获得卡内基教学学院地位的目标。

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.