CAREER: Building a Mechanistic Understanding of Mechanochemically Adaptive Polymers

这个教师早期职业发展（CAREER）奖将调查的物理机制如何机械化学响应均聚物适应响应外部负载。聚合物-塑料和橡胶-在商业和工业上广泛使用。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，大多数聚合物开发都集中在改善材料的初始性能，如刚度和强度。然而，最终这些材料性能会退化。考虑到这些材料在其寿命期间所经历的各种各样的和有些不可预测的负载，预测这种退化将在何时何地发生是非常困难的。因此，目前的结构设计过度。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对损伤的发生做出反应;这些被称为机械化学响应聚合物。这样的材料将具有更长的寿命，并且特别是不易受到通过高强度短持续时间负载（诸如头盔冲击）的累积损坏的影响。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。将与纽约4 H计划协调制定研究启发的外展计划，从而在纽约年度州博览会上举办一个展位。还将为本科生材料力学课程开发一个可搜索的概念问题数据库，并将其分发给其他学术机构。机械化学响应聚合物可以通过共价结合机械载体-化学单元来实现，这些化学单元在响应所施加的力时进行特定的化学转化。鉴于其独特的机制，弹性体和玻璃态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处理。对于弹性体，基于力学元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，并且该模型的关键方面将通过现有材料系统进行实验验证。对于玻璃态聚合物的聚合物基质上的机械动力学的约束将通过光响应的机械动力学实验探测，机械动力学响应应力将建模和实验验证在连续水平，并通过分析和分子动力学方法评估自我增强和自我修复的潜力。PI开发的理论和方法将为机械力化学响应聚合物设计奠定基础。这项工作的各个方面，关注如何打破一个聚合物内的键也将有聚合物断裂的影响。

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.