SGER: Stress Relaxation Mechanisms in End-Linked Main-Chain Smectic Elastomers

技术概述：液晶弹性体（LCE）是橡胶状聚合物网络，由于介晶有序的存在，其表现出与普通橡胶弹性的强烈偏离。 “主链”近晶LCE由于嵌入网络链的主链中而形成层状中间相，表现出复杂的动态力学行为，具有宽的弛豫时间谱。 通过非线性缩聚制备的主链近晶弹性体的最新研究在理解其动态力学响应方面取得了一些进展，但进一步的进展取决于实现对交联之间的弹性链的摩尔质量分布（Mc）的更好控制。 该SGER涉及通过末端连接来合成具有挑战性的结构上明确定义的近晶LCE，这允许控制Mc。 将合成具有最小缺陷量的“模型”末端连接网络和具有故意引入的侧链或自由链的“不完美”网络。 端部连接的MCLCE的力学性能的特点是小应变振荡变形和拉伸应力松弛。 近晶材料与非晶材料的畴尺寸和体积分数将通过X射线衍射表征。 比较模型和不完美的弹性体将揭示如何节段级或域级松弛过程是绑在宏观动态力学响应。 这项研究将是第一个使用端连接网络来整理出近晶LCE中的松弛过程的复杂阵列，提供了潜在的催化快速和创新的进步，在理解液晶聚合物networks.Non-Technical摘要：主链液晶弹性体（MCLCE）的物理是联合收割机相结合的灵活性和韧性的橡胶状聚合物与液晶的分子有序的材料。 MCLCE具有独特的机械性能，可能使其用作振动阻尼或冲击吸收橡胶涂层，或用作具有类似于肌肉组织特性的软致动器。 为了更好地理解分子结构和宏观性质之间的联系，必须研究具有受控化学结构和最小缺陷量的“模型”MCLCE。 这项SGER资助支持通过一种称为末端连接的技术制备MCLCE模型，随后将进行旨在表征其物理特性的实验研究。 该项目将推进对近晶MCLCE的基本理解，其在纳米尺度上具有分层有序性。 这项研究支持了宾夕法尼亚州立大学有价值的教育活动，包括研究生和本科生研究，支持积极参与外展计划的学生的工作，这些计划向妇女和高中生介绍聚合物和材料科学。

TECHNICAL SUMMARY:Liquid crystalline elastomers (LCE) are rubber-like polymer networks that exhibit strong deviations from ordinary rubber elasticity due to the presence of mesomorphic ordering. "Main-chain" smectic LCE, which form lamellar mesophases due to mesogens embedded in the backbones of the network chains, exhibit complex dynamic mechanical behavior with broad relaxation time spectra. Recent studies of main-chain smectic elastomers prepared by non-linear polycondensation made some progress in understanding their dynamic mechanical response, but further progress depends on achieving better control over the molar mass distribution of elastic chains between crosslinks (Mc). This SGER involves a challenging synthesis of architecturally well-defined smectic LCE by end-linking, which allows control of Mc. "Model" end-linked networks having minimal amounts of defects and "imperfect" networks having deliberately introduced pendant or free chains will be synthesized. Mechanical properties of end-linked MCLCE will be characterized by small-strain oscillatory deformation and tensile stress relaxation. Domain size and the volume fraction of smectic vs. amorphous material will be characterized by X-ray diffraction. Comparing model and imperfect elastomers will reveal how segment-level or domain-level relaxation processes are tied to macroscopic dynamic mechanical response. This study will be the first to use end-linked networks to sort out the complex array of relaxation processes in smectic LCE, offering the potential to catalyze rapid and innovative advances in understanding the physics of liquid crystalline polymer networks.NON-TECHNICAL SUMMARY:Main-chain liquid crystalline elastomers (MCLCE) are materials that combine the flexibility and toughness of a rubber-like polymer with the molecular ordering of liquid crystals. MCLCE have unique mechanical properties that potentially make them useful as vibration damping or impact-absorbing rubber coatings, or as soft actuators with properties similar to muscle tissue. To better understand the connections between molecular structure and macroscopic properties, "model" MCLCE with controlled chemical structures and minimal amounts of defects must be studied. This SGER grant supports preparation of model MCLCE by a technique called end-linking, which will be followed by experimental research aimed at characterizing their physical properties. The project will advance basic understanding of smectic MCLCE, which have layered ordering at the nanometer scale. The research supports valuable educational activities at Penn State University including graduate and undergraduate research, supporting the work of students who actively participate in outreach programs that introduce women and high-school students to polymers and materials science.