Viscoelastic Properties of Liquid Crystal Polymers and Polymer Networks in Nematic Solvents

本项目探讨了大分子结构对液体聚合物（LCP）和LCP网络在低摩尔质量向列溶剂中的粘弹性行为的影响。先前对不同结构lcp的稀向列溶液性质的研究揭示了各种新的粘度现象，例如lcp诱导的流对准和流翻滚状态之间的转变。为了定量地解释这些观察结果，有必要引入一种新的粘性耗散机制，这种机制不存在于各向同性解中，它源于指向性旋转和LCP主干构型之间的机械耦合。首先，向列溶液中侧链lcp的进一步研究，包括定向器旋转速率的conconscopic光学分析，以及链尺寸的直接测定和弛豫分子理论。其次，我们试图证实理论预期，即对于由向列溶剂膨胀的LCP网络，在溶剂的扭曲弹性和LCP网络的熵弹性之间存在力学耦合。第三，在较高的LCP浓度下，将探索新的动力学现象：例如，链缠结弹性的开始以及流动与LCP和溶剂的顺序参数的耦合可能导致场或应力诱导的结构转变。这些研究将探索含有聚合物的向列材料的粘弹性行为的新现象，并将基于lcp在向列溶剂中的溶液或凝胶，为器件应用的新材料设计提供相关信息。

This project explores the effect of macromolecular structure on the viscoelastic behavior of liquid polymers (LCPs) and LCP networks in low molar mass nematic solvents. Previous research on the properties of dilute nematic solutions of LCPs of varying architectures uncovered a variety of novel viscometric phenomena, such as LCP-induced transitions between flow-aligning and flow-tumbling states. To explain these observations quantitatively, it is necessary to introduce a new viscous dissipation mechanism, not present in isotropic solutions, which derives from a mechanical coupling between director rotation and LCP backbone configuration. First, further studies of side-chain LCPs in nematic solution, including conoscopic optical analysis of the rate of director rotation, as well as direct determinations of chain dimensions and the relaxation molecular theory. Second, we seek to confirm the theoretical expectation that, for LCP networks swollen by a nematic solvent, there is a mechanical coupling between the distortional elasticity of the solvent, and the entropic elasticity of the LCP network. Third, new dynamical phenomena at higher LCP concentrations will be explored: e.g. the onset of chain entanglement elasticity and the coupling of the flow to the order parameters of LCP and solvent may lead to field- or stress-induced structural transitions.%%%These studies will explore new phenomena in the viscoelastic behavior of nematic materials containing polymers, and will generate information pertinent to the design of novel materials for device applications, based on solutions or gels of LCPs in nematic solvents.