Investigating the Molecular Mechanisms of Thermally Active Amorphous Shape Memory Polymers

热致形状记忆聚合物是一种灵活的智能材料，可以通过产生形状变化来响应特定的温度事件。支持非晶形状记忆聚合物行为的分子机制是由玻璃化转变引起的聚合物链迁移率的剧烈变化。在高温下，链是可移动的，可以重新排列，例如，通过链段的旋转或扩散，以达到平衡结构和应力状态，以响应温度变化或施加的载荷。当聚合物冷却到低于玻璃化转变温度时，迁移率消失。这限制了结构和应力松弛机制，允许材料存储临时形状。再加热到高于转变温度恢复流动性，使材料放松并恢复永久形状。本研究的目标是：(1)对温度相关的结构和应力松弛机制对热诱导形状记忆聚合物性能的重要性有一个基本的认识；(2)确定关键的热力学参数并量化它们对形状记忆性能的影响。本研究将开发的基本理解、建模和计算工具，通过降低设计和制造成本以及实现新的集成功能，有可能影响广泛的技术。这些技术包括多功能形状记忆聚合物医疗设备，集成传感器和执行器，以及可展开的航空航天结构。本项目将研究活动整合到材料力学和数值方法的基础工程课程中，将有利于工程教育。此外，将招募妇女和少数民族参加研究活动，以促进代表性不足的群体参与智能材料力学领域。

Investigating the Molecular Mechanisms of Thermally Active Amorphous Shape Memory Polymers Thermally induced shape memory polymers are flexible smart materials that respond to a specific temperature event by generating a shape change. The molecular mechanism underpinning the behavior of amorphous shape memory polymers is the dramatic change in the mobility of the polymer chains induced by the glass transition. At high temperature, the chains are mobile and can rearrange, e.g., through rotation or diffusion of chain segments, to an equilibrium structure and stress state in response to a temperature change or applied load. The mobility vanishes as the polymer is cooled to below the glass transition temperature. This curtails structural and stress relaxation mechanisms allowing the material to store a temporary shape. Reheating to above the transition temperature restores the mobility allowing the material to relax and recover the permanent shape. The objectives of this proposal are: (1) to develop a fundamental understanding of the importance of the temperature-dependent structural and stress relaxation mechanisms on the performance of thermally induced shape memory polymers, and (2) to identify key thermomechanical parameters and quantify their effects on the shape memory performance. The fundamental understanding, and the modeling and computational tools, which will be developed, by this research has the potential to impact a broad range of technologies by reducing the design and manufacturing costs and enabling new and integrated functionalities. These technologies include multifunctional shape memory polymer medical devices, integrated sensors and actuators, and deployable aerospace structures. This project will benefit engineering education by integrating the research activities into fundamental engineering classes on mechanics of materials, and numerical methods. In addition, women and minorities will be recruited for the research activities to promote the participation of underrepresentative groups in the area of smart materials mechanics.