CAREER: Building a Mechanistic Understanding of Mechanochemically Adaptive Polymers

这个学院早期职业发展（Career）奖将研究控制机械化学反应均聚物如何适应外部负载的物理机制。聚合物——包括塑料和橡胶——在商业和工业上有着广泛的应用。应用包括轮胎、头盔、游乐场设备、飞机和医疗设备等安全关键产品。迄今为止，大多数聚合物的开发都集中在改善材料的初始性能，如刚度和强度。然而，这些材料的性能最终会退化。考虑到这些材料在其生命周期中所经历的各种不可预测的载荷，预测何时何地会发生这种降解是非常困难的。因此，目前的结构是过度设计的。该奖项支持对聚合物的研究，这些聚合物将在分子尺度上增强，通过局部增强自身来应对损伤的发生；这些被称为机械化学反应性聚合物。这样的材料将具有更长的寿命，特别是不易受到高强度短时间载荷（如头盔撞击）的累积损伤。这种材料概念将减少浪费，减轻结构重量，并降低安全关键应用的检查成本。研究启发的外展计划将与纽约4H计划协调发展，最终在纽约年度州博览会上设立一个摊位。还将为本科材料力学课程开发一个可搜索的概念问题数据库，并分发给其他学术机构。机械化学反应聚合物可以通过机械基团的共价结合来实现，机械基团是一种化学单位，在外力作用下发生特定的化学转变。鉴于其独特的机制，弹性体和玻璃状聚合物都被视为一个重点领域，将通过理论、模拟和实验相结合的方法来研究。对于弹性体，基于机械团的动态网络将被明确地模拟，简化为有限元实现的本构模型，模型的关键方面将用现有的材料系统进行实验验证。对于玻璃聚合物，聚合物基质对机械团动力学的约束将通过光响应机械团进行实验探索，机械团对应力的响应将在连续体水平上进行建模和实验验证，并通过分析和分子动力学方法评估自我强化和自我修复的潜力。PI开发的理论和方法将为机械化学反应聚合物的设计奠定基础。这项工作涉及到聚合物中键如何断裂的方面也将对聚合物断裂产生影响。

This Faculty Early Career Development (CAREER) award will investigate the physical mechanisms governing how mechanochemically responsive homopolymers adapt in response to external loading. Polymers - both plastics and rubbers - are widely used commercially and industrially. Applications include such safety-critical products as tires, helmets, playground equipment, airplanes, and medical devices. Most polymer development to date has focused on improving initial properties of the material such as stiffness and strength. However, eventually these material properties degrade. Given the diverse and somewhat unpredictable loads that these materials experience over their lifetime, it is incredibly difficult to predict when and where this degradation will occur. Currently structures are therefore overdesigned. This award supports research into polymers that would be augmented on the molecular scale to react to the onset of damage by strengthening themselves locally; these are referred to as mechanochemically responsive polymers. Such materials would have longer lifespans and in particular be less susceptible to accumulated damage through high intensity short duration loads (such as helmet impact). This material concept will lead to reduced waste, reduced weight of structures, and reduced inspection costs for safety-critical applications. Research-inspired outreach programs will be developed in coordination with the New York 4H program, resulting in a booth to be held at the NY annual state fair. A searchable database of concept questions for undergraduate mechanics of materials courses will also be developed and disseminated to other academic institutions.Mechanochemically responsive polymers can be realized through the covalent incorporation of mechanophores - chemical units that undergo a specific chemical transformation in response to applied force. Given their distinct mechanisms, elastomers and glassy polymers are each taken as a focus area that will be approached through a combined theory, simulation, and experimental approach. For elastomers the mechanophore-based dynamic networks will be explicitly simulated, reduced to a finite element implemented constitutive model, and key aspects of the model will be experimentally validated with existing materials systems. For glassy polymers the constraint of the polymer matrix on mechanophore kinetics will be experimentally probed through light responsive mechanophores, mechanophore response to stress will be modeled and experimentally validated at the continuum level, and potential for self-strengthening and self-healing will be assessed through analytical and molecular dynamics approaches. The theory and methods developed by the PI will lay the groundwork for mechanochemically responsive polymer design. The aspects of this work that concern how bonds break within a polymer will also have implications for polymer fracture.