Rheological, Rheooptical and Physical Chemical Studies on Nematic Polymers and their Solutions

向列型聚合物及其溶液的流变学、流变光学和物理化学研究

• 批准号: 9417374
• 负责人: Guy Berry
• 金额: $ 30万
• 依托单位: Carnegie-Mellon University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-01-15 至 1998-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9417374&HistoricalAwards=false
• 关键词: Rheological; Rheooptical; Physical; Chemical; Studies

9417374 Berry Rheological and rheooptical studies are being carried out on nematic polymers and their solutions. The linear and nonlinear viscoelastic properties of this technologically important class of materials are complex owing to the inherent anisotropy of the properties of an ordered, nematic phase. Four nematogenic polymers are to be studied to provide a systematic variation in the molecular characteristics giving rise to nematic order. Three of the systems are solutions of chains with large persistence lengths characterizing their conformation, but with differing degrees of rigidity to the molecular conformation. Two have high rigidity of structure, but with persistence lengths differing by a factor of two: poly (1,4-phenylene- 2,6-benzobisthiazole), PBZT, and poly (1,4-phenylene-2,6- benzobisoxazole), PBZO, with the former having the higher persistence length. The third, poly(1,4-phenylene- terephthalate, has a persistence length similar to PBZO, but is believed to have a less rigid structure. The fourth sample is a poly(1-olefin sulfone) known to form an ordered fluid over a range of temperatures. The proposed studies include static and dynamic light scattering on aligned monodomains to determine the Frank curvature elasticities for distortion of the director field, and associated viscosities, as functions of chain length, concentration and other variables. Third harmonic generation on the same samples will be used to assess surface layers of special alignment, including a biaxial nematic alignment, that may be important to rheological behavior. The emphasis will be on the use of creep and recovery and rheooptical measurements on nematic preparations, with no prior treatment to induce overall alignment, augmented by studies on monodomain samples to determine whether the preparations align in a slow shear flow. %%% The rheology of isotropic solutions of nematogenic polymers comprising rodlike sequences catenated by monomers imparting a no n rodlike linkage will also be studied. The study is directed to elucidation of aspects of the molecular dynamics of semiflexible chains. It is postulated that chains may exhibit a marked suppression in molecular mobility, perhaps leading to a structural glass similar to one proposed theoretically, but never found, for nematogenic rodlike polymers. This could occur owing to the severe restriction to rotational motions expected for each of the rodlike subunits, leading to an overall suppression of molecular diffusion, and solid-like behavior under small stresses. A yield behavior to fluid-like behavior is anticipated at larger stresses, owing to the relatively weak intermolecular interactions leading to the structural glass.

小行星9417374 流变学和流变光学的研究正在进行的聚合物及其解决方案。 这类技术上重要的材料的线性和非线性粘弹性性质是复杂的，这是由于有序的非线性相的性质的固有各向异性。 要研究的四个致热聚合物提供了一个系统的变化，在分子特性引起的热有序。 三个系统的解决方案的链具有大的持久性长度表征其构象，但不同程度的刚性的分子构象。 两种具有高的结构刚性，但持久性长度相差两倍：聚（1，4-亚苯基-2，6-苯并二噻唑），PBZT和聚（1，4-亚苯基-2，6-苯并二恶唑），PBZO，前者具有更高的持久性长度。 第三种是聚（1，4-亚苯基-对苯二甲酸酯），具有类似于PBZO的持久长度，但据信具有较低的刚性结构. 第四个样品是已知在一定温度范围内形成有序流体的聚（1-烯烃砜）。 建议的研究包括静态和动态光散射对齐monodomains，以确定弗兰克曲率弹性的导演场的扭曲，和相关的粘度，作为链长，浓度和其他变量的函数。 在相同样品上的三次谐波产生将用于评估特殊排列的表面层，包括可能对流变行为很重要的双轴向排列。 重点将是使用的蠕变和恢复和流变光学测量的制备，没有事先处理，以诱导整体对齐，增强了单域样品的研究，以确定是否在一个缓慢的剪切流的制剂对齐。 还将研究包含由赋予非棒状键的单体链连接的棒状序列的致热聚合物的各向同性溶液的流变性。 这项研究是针对阐明方面的分子动力学的半柔性链。 据推测，链可能会表现出显着的抑制分子的流动性，也许会导致一个类似的结构玻璃理论上提出的，但从未发现过，为致热棒状聚合物。 这可能是由于对每个棒状亚基预期的旋转运动的严格限制，导致分子扩散的整体抑制，以及在小应力下的固体样行为。 由于相对较弱的分子间相互作用导致结构玻璃，预期在较大的应力下屈服行为为流体状行为。