Fighting Fatigue and Fracture with Morphologically Tuned Energy Dissipation in Highly Swollen Elastomer Networks

第1部分：非技术概述膨胀弹性体网络是一种聚合物材料，在促进健康、能源和环境应用方面具有关键作用。这些包括生物软组织替代材料，如在膝关节半月板或脊柱椎间盘中发现的材料，选择性去除化学或生物污染物的分离膜，用于电池技术的耐用和快速离子传输膜，以及旨在提供长期冲击保护（军事，体育）同时保持高弹性柔韧性的材料。然而，由于材料的能力有限，无法满足此类应用所需的机械要求，因此在实践中一直受到困扰，这些材料的弹性会迅速衰减，并且容易因断裂而失效。该项目专注于使用膨胀弹性体网络设计的新范例，以创建机械坚固的聚合物，能够维持重复应力消散而不会疲劳，同时抑制断裂和失效的易感性，以确保长期性能。项目的科学进步工作将与学生的跨学科教育相结合。它还将伴随着研讨会的发展，旨在建立世界各地顶级软物质合成和力学小组之间的合作，努力推动科学的前沿，探索新的想法，并加速这些独特的聚合物材料的未开发潜力。重要的是，这些研讨会将提供一个论坛，鼓励有才华但代表性不足的年轻研究人员，并为他们提供接触世界领先材料研究人员的机会和指导。在过去的十年中，聚合物网络设计的创造性努力导致了水凝胶力学的许多有影响的改进。值得注意的例子包括高弹性水凝胶网络，其疲劳最小，但能量耗散很少；高耗散水凝胶网络，其韧性最大化，但疲劳很快，恢复需要很长的恢复时间（几分钟到几天）。然而，利用当前的设计策略，有效整合耗散能力和有效弹性恢复似乎是有限的。本提案的主要目标是展示连接点形态（纳米结构）和链级组织控制的能力，以最大限度地提高膨胀聚合物网络中非塑性能量耗散、恢复速率和抗疲劳性。本研究的中心假设是，将非键断裂耗散相互作用合成集成到网络的每条分子链中，并将耗散机制与其自身弹性恢复驱动力的隐式耦合结合起来，将在不牺牲快速弹性恢复或优异的抗疲劳性的情况下增加大量的耗散能力。该项目涉及独特设计的ABC和ABCBA嵌段共聚物的合成开发，这些共聚物在加热后自组装成基于核-壳球体形态的高效网络结构。目的是探索B块畴尺寸和疏水性程度成功调节耗散能量大小的能力（例如，通过测量断裂韧性），并了解其对应变和应变速率的依赖。如果成功，该项目将改变我们对具有抗疲劳性和韧性（体积和断裂）的水凝胶材料的获取方式，其恢复速度远远超过迄今为止开发的最先进的水凝胶系统。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYSwollen elastomer networks are polymeric materials that have the potential to play key roles in advancing of a number of health, energy, and environmental applications. These include biological soft-tissue replacement materials such as those found in the meniscus of the knee or the intervertebral disc of the spine, separation membranes for selective removal of chemical or biological contaminants, durable and rapid ion-transport membranes for battery technology, and materials designed to provide long-term impact protection (military, athletics) while retaining high elastic flexibility. Reduction to practice, however, has been plagued by materials with limited ability to meet the mechanical demands required of such applications, being subject to rapid decay in elasticity and susceptibility to failure by fracture. This project is focused on using a new paradigm in swollen elastomer network design to create mechanically robust polymers capable of sustaining repetitive stress dissipation without fatigue while suppressing susceptibility to fracture and failure needed to ensure long-term performance. The scientific advancement efforts in the project will be integrated with interdisciplinary education of students. It will also be accompanied by development of workshops aimed at building collaborations among top soft-matter synthesis and mechanics groups around the world, in an effort to push the frontiers of science, explore new ideas, and accelerate the untapped potential of these unique polymeric materials. The workshops importantly will provide a forum to encourage talented, yet underrepresented young researchers, and provide them access to and mentorship from leading materials researchers in the world.PART 2: TECHNICAL SUMMARYCreative efforts in polymer network design over the last decade have led to numerous impactful improvements in hydrogel mechanics. Notable examples include both highly elastic hydrogel networks in which fatigue is minimal but very little energy is dissipated, and highly dissipative hydrogel networks in which toughness is maximized but fatigue is rapid and recovery is subject to long recovery times (minutes to days). Effective integration of both dissipative capabilities and efficient elastic recovery, however, appears limited using current design strategies. The principal objective of this proposal is to demonstrate the ability of junction point morphology (nanostructure) and strand-level organizational control to maximize non-plastic energy dissipation, recovery rate, and fatigue resistance simultaneously in swollen polymer networks. The central hypothesis of the proposed research is that synthetic integration of non-bond rupturing dissipative interactions into every molecular strand of the network, combined with implicit coupling of the dissipation mechanism to its own driving force for elastic recovery, will add substantial dissipative capability without sacrificing the rapid elastic recovery or the exceptional fatigue resistance. The project involves the synthetic development of uniquely designed ABC and ABCBA block copolymers which upon heating self-assemble into highly efficient network structures based on core-shell sphere morphologies. The objectives are to explore the ability of the B block domain size and degree of hydrophobicity to successfully tune the magnitude of dissipated energy (e.g., through measurement of fracture toughness) and understand its dependence on strain and strain rate. If successful, this project will transform our access to hydrogel materials that exhibit both fatigue resistance and toughness (bulk and fracture), at rates of recovery far exceeding the most advanced hydrogel systems developed to date.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.