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

液晶和刚性棒聚合物混合物中相分离和中间相相变的动力学

• 批准号: 9903519
• 负责人: Thein Kyu
• 金额: $ 28.2万
• 依托单位: University of Akron
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-07-01 至 2002-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9903519&HistoricalAwards=false
• 关键词: Dynamics; Phase; Separation; Mesophase; Transition

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.

本发明涉及由液晶（LC）和液晶聚合物（LCP）组成的聚合物复合材料和电光材料。 聚合物分散液晶（PDLC）的电光性能与液晶畴的形态和分散性密切相关。 本研究试图通过控制液晶相的形态，对聚合物分散液晶的电光性能有一个基本的认识。 重点已放在确定的作用，LC/聚合物混合物的热力学相图上的最终形态，包括LC分散体和新兴的域的大小。 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，相分离动力学和有序化动力学之间的竞争将被研究。 这一建议包括实验和理论阐明（i）在液晶和侧链液晶中的相变动力学和临界现象（或刚性杆）聚合物，（ii）链刚性对含有侧链和主链液晶聚合物的二元向列相的相分离动力学的影响，（iii）由热淬灭或化学反应驱动的近晶相LC/聚合物共混物中的中间相有序动力学和相分离动力学之间的竞争，以及（iv）刚性棒状聚合物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，基于时间依赖的Ginzburg-Landau方程（TGDL -模型C），已经开发了液晶/聚合物混合物中的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有序（液晶有序）参数之间的耦合。 本文提出将各向同性混合的Flory-Huggins（FH）理论和近晶有序的Maier-Saupe（MS）自由能泛函（或近晶有序的Maier-Saupe-McMillan（MSM）理论）结合到TDGL方程中。将阐明与耦合TDGL -模型C方程有关的所有参数的物理意义，并证明其预测能力。 图案形成的动力学将与最近的实验观察进行比较分析。 认识到可能的控制域形态和介晶相互作用的理解，拟议的研究将扩展到纳米复合材料。 如果成功的话，所提出的理论将减轻一些问题，如反复试验的方法，导致所需的域形态的不可再现性和低产量的PDLC film.During这十年中，我们已经目睹了一个巨大的增长液晶为基础的光学器件，如平板显示器。 在新的千年，对先进有机和聚合物电光材料的需求预计将增加。 这一领域的平板显示器一直占主导地位的远东国家，主要是日本。 重要的是，美国通过在这一不断增长和有前途的技术方面进行开创性的基础研究来保持其竞争优势。 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投影仪的帮助下以实时模式显示LC畴形态的出现。 这样的互动程序是有用的课堂教学，因此应该是非常有益的未来的科学家和工程师在美国的培训。 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。