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）形状记忆行为的悬而未决的问题，最近研究人员发现液晶和半结晶网络都存在。 可逆形状记忆是指在较小的外加应力作用下，试样经历加热诱导收缩和冷却诱导伸长的过程，该过程可以无限重复，以将热量转化为功。虽然这一现象令人兴奋，在软驱动装置中具有巨大的潜在用途，并且可能在有序聚合物网络中具有普遍性，但需要进行基础研究以阐明行为的潜在机制。因此，合作研究人员设想将材料合成和固体流变学表征（美国）与详细的原位微观结构表征（墨西哥）相结合，这将导致定量和机械理解，将分子结构，分子相互作用，纳米结构和热机械响应联系起来。使用现代实验方法，研究人员建立设计原则，指导新的形状记忆聚合物和加工方案的开发。通过采用多种材料系统之间的比较分析方法，研究人员预计通用热弹性机制和系统特定行为的识别。 研究人员进一步奋进以创造性设备的形式开发双向形状记忆行为，包括设计，制造和测试。通过美国（Mather实验室）和墨西哥（Romo-Uribe实验室）之间的本科生，研究生和博士后研究人员的重要交流，合作发挥作用，产生广泛的技术和文化教育。网络材料将在美国合成，而材料的原位X射线变形研究将在墨西哥进行。作为一项推广活动，研究人员建立了CyberSTRETCH，这是一个远程仪器控制系统，可增强协作，并为初中和高中科学，物理或化学课程远程访问弹性体拉伸测试提供广泛的影响潜力，揭示材料，强度和机械设计的概念。该奖项与NSF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.