Effects of Energetic and Entropic Disparities on the Properties of Elastomers

技术总结所提出的工作的目标是提供一个详细的和基本的了解如何熵和能量的影响可以利用来操纵弹性行为的末端连接的聚合物网络。从设计的角度来看，能量效应很容易通过在选定的组分中引入化学差异来调节，而熵链间相互作用可以通过改变系统中的分子量分布和缠结程度来强烈影响。因此，模型网络将在不同的条件下合成和表征，以解决三个问题：1）在多大程度上可以提高网络的韧性，表现出熵驱动的有序-无序微相分离，通过耦合这种分离与能量的力量所产生的化学差异链和交联？2)链长多峰性所带来的熵差对网络结构和力学性能有何影响？3)链的散布和缠结（均为熵链相互作用）对橡胶弹性和韧性的影响是什么？- 明智地选择聚（二乙基硅氧烷）弹性体中的交联剂可以导致交联之间的能量吸引，并导致这些材料的韧性增加。合成和表征的努力沿着与粗粒度的计算机模型将进行这一目的。其次，将沿着计算机模拟使用对标记了多峰弹性体的不同组分的样品的氘NMR测量，以提供对多峰结构的增加的韧性的理解。最后，将进行实验和模拟，以研究被捕获的缠结和链散布对弹性体的机械性能的不同作用。非技术概述弹性体是弹性材料，例如在软接触镜、轮胎、橡皮筋、某些生物医学装置、O形环、这项研究的重点是组成这些弹性体的聚合物分子的性质如何影响它们的最终用途，以及可以做些什么来改进这些材料或开发新的材料。特别感兴趣的是合成模拟天然物质（如肌肉蛋白肌联蛋白）的机械行为的弹性体，其表现出吸收大量变形能量而不断裂的能力（例如，用于需要在严重应力下的软材料的应用）。 研究生和本科生将直接参与这项研究，为他们提供聚合物科学和工程一般领域的教育和研究培训。主要研究者将参加教育推广活动，如为纽约北部高中教师举办的材料研讨会和为高中女生举办的居里学院。

TECHNICAL SUMMARYThe goal of the proposed work is to provide a detailed and basic understanding on how entropic and energetic effects can be harnessed to manipulate elastic behavior of end-linked polymer networks. From a design perspective, energetic effects are readily tunable by introducing chemical disparity in selected components, while entropic inter-chain interactions can be strongly influenced by changing the molecular weight distribution and the extent of entanglements in the system. Accordingly, model networks will be synthesized under different conditions and characterized to address three questions: 1) To what extent can one enhance the toughness of networks that exhibit entropy-driven order-disorder microphase segregation by coupling such segregation with energetic forces arising from a chemical disparity between chains and crosslinks? 2) What is the effect of the entropic disparity brought about by chain length multimodality on network structure and mechanical properties? 3) What is the interplay between chain interspersion and entanglements (both entropic chain interactions) on rubber elasticity and toughness? - A judicious choice of cross-linkers in poly(diethylsiloxane) elastomers can result in energetic attraction between the cross-links and lead to increased toughness in these materials. Synthetic and characterization efforts along with coarse-grained computer models will be carried out for this purpose. Secondly, deuterium NMR measurements on samples where different components of multimodal elastomers are labeled will be used along with computer simulations to provide an understanding of the increased toughness of multimodal structures. Finally, experiments and simulations will be carried out to investigate the different roles of trapped entanglements and chain interspersion on the mechanical properties of elastomers.NON-TECHNICAL SUMMARYElastomers are elastic materials such as those encountered in soft contact lenses, tires, rubber bands, certain biomedical devices, O-rings, etc. This research focuses on how the properties of the polymer molecules that make up these elastomers affect their end-use and what can be done to improve these materials or develop new ones. Of particular interest would be the synthesis of an elastomer that mimics the mechanical behavior of natural substances, like the muscle protein titin, that exhibit the ability to absorb large amounts of deforming energy without breaking (e.g., for applications entailing soft materials under severe stresses). Students, both graduate and undergraduate, will be directly involved in this research that will provide them with educational and research training in the general area of polymer science and engineering. The Principal Investigators will participate in educational outreach activities such as Materials Workshops for upstate New York high school teachers and the Curie Academy for high school girls.