Materials World Network: Anomalous Thermoelasticity in Liquid Crystalline and Semicrystalline Polymer Networks

美国和墨西哥UNAM-Cuernavaca之间的美洲合作解决了有关有序聚合物中可逆（双向）形状记忆行为的突出问题，最近研究人员发现液晶和半晶体网络都存在。可逆形状记忆是这样一个过程，在一个小的施加应力下，试样经历加热引起的收缩和冷却引起的延伸，这个过程可以无限期地重复，以将热量转化为功。虽然这种现象令人兴奋，在软驱动装置中有很大的潜在应用，并且可能在有序聚合物网络中普遍存在，但需要进行基础研究来阐明这种行为的潜在机制。因此，合作研究人员设想将材料合成和固体流变表征（美国）与详细的原位微结构表征（墨西哥）结合起来，这将导致分子结构、分子相互作用、纳米结构和热机械响应之间的定量和机理理解。使用现代实验方法，研究者建立设计原则，指导新的形状记忆聚合物和加工方案的发展。通过采用多种材料系统之间的比较分析方法，研究人员预测了通用热弹性机制和系统特定行为的识别。研究人员进一步努力利用双向形状记忆行为的发明设备的形式，包括设计，制造和测试。美国（Mather的实验室）和墨西哥（Romo-Uribe的实验室）通过本科生、研究生和博士后研究人员的大量交流，开展了广泛的技术和文化教育。网络材料的合成将在美国进行，而材料的现场x射线变形研究将在墨西哥进行。作为一项拓展活动，研究人员建立了远程仪器控制系统CyberSTRETCH，该系统加强了协作，并为初中和高中科学、物理或化学课程的弹性体拉伸测试提供了广泛的影响潜力，揭示了材料、强度和机械设计的概念。该奖项与美国国家科学基金会国际科学与工程办公室共同资助。

This Inter-American collaboration between the US and UNAM-Cuernavaca in Mexico addresses outstanding questions concerning reversible (two-way) shape memory behavior in ordered polymers, recently discovered by the investigators to exist for both liquid crystalline and semicrystalline networks. Reversible shape memory is the process whereby, under a small applied stress, specimens undergo heating-induced contraction and cooling-induced elongation a sequence that can be repeated indefinitely for conversion of heat to work. While the phenomenon is exciting, of great potential use in soft actuation devices, and possibly universal among ordered polymer networks, fundamental studies are required to elucidate underlying mechanisms of the behavior. Thus, the collaborating investigators have conceived combining materials synthesis and solid-rheological characterization (US) with detailed, in-situ, microstructural characterization (Mexico) that will lead to quantitative and mechanistic understanding that connects molecular architecture, molecular interactions, nanostructure, and thermo-mechanical response. Using modern experimental approaches, the investigator establish design principles that guide the development of new shape memory polymers and processing schemes alike. By adopting a comparative analysis approach among multiple materials systems, the researchers anticipate discernment of both universal thermoelastic mechanisms and system-specific behavior. The investigators further endeavor to exploit the two-way shape memory behavior in the form of inventive devices, including design, fabrication, and testing.The collaboration functions through significant exchange of undergraduate, graduate, and postdoctoral researchers between the US (Mather's lab) and Mexico (Romo-Uribe's lab), engendering broad technical and cultural education alike. Network materials will be synthesized in the US, while in-situ x-ray deformation studies on the materials will be conducted in Mexico. As an outreach activity, the investigators establish CyberSTRETCH, a system for remote instrument control that enhances the collaboration and offers the broad impact potential for remote access to elastomer tensile testing for middle school and high school science, physics, or chemistry classes, revealing concepts of materials, strength, and mechanical design.This award is co-funded with the NSF Office of International Science and Engineering.