CAREER: Building a Mechanistic Understanding of Mechanochemically Adaptive Polymers

这项学院早期职业发展(CALEAR)奖将研究控制机械力化学响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--在商业和工业上得到了广泛的应用。应用包括轮胎、头盔、游乐场设备、飞机和医疗器械等安全关键产品。到目前为止，大多数聚合物的开发都集中在改善材料的初始性能，如硬度和强度。然而，这些材料的特性最终会退化。鉴于这些材料在其生命周期中经历的各种和某种程度上不可预测的载荷，预测这种降解将在何时何地发生是令人难以置信的困难。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水平上得到增强，通过在局部增强自身来对损害的开始做出反应；这些聚合物被称为机械力化学响应性聚合物。这种材料的寿命更长，尤其不容易受到高强度短时间载荷(如头盔撞击)造成的累积损害。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。受研究启发的外展计划将与纽约4H计划协调发展，从而在纽约年度州博览会上设立一个展位。还将为材料力学本科生课程开发一个可搜索的概念问题数据库，并将其传播给其他学术机构。机械力化学响应性聚合物可以通过机械力-化学单元在外力作用下发生特定化学转化的共价结合来实现。鉴于其不同的机理，弹性体和玻璃态聚合物分别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进行探讨。对于弹性体，基于机械量的动态网络将被显式地模拟，简化为有限元实现的本构模型，并且该模型的关键方面将用现有的材料系统进行实验验证。对于玻璃态聚合物，将通过光响应性机械团来实验探索聚合物基质对机械团动力学的约束，将在连续介质水平上对机械团对应力的响应进行建模和实验验证，并将通过分析和分子动力学方法来评估自我增强和自我修复的潜力。PI发展的理论和方法将为机械力化学响应型聚合物设计奠定基础。这项工作涉及聚合物中的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.