Building a Platform of Impact-Energy Absorbing Materials: How Molecular Manipulations Translate into Macroscopic Properties

非技术总结：聚合物的一个独特特性是它们在撞击事件中吸收机械能的能力，这种能力是通过将能量转化为单个聚合物链的分子运动来实现的。该项目的重点是研究吸能聚合物平台的基本材料特性，并开发一个工具箱来引入分子机制，以增加韧性、能量耗散和纳米级自愈的潜力，从而延长材料的寿命。该平台基于称为“巯基网络热固性”的聚合物网络材料。它们可以通过提供快速反应时间和高度均匀网络的化学方法制造，就像链式围栏一样，从而产生高能量吸收能力。Savin小组之前的工作已经证明了在网络中进行分子水平变化的能力，并将其转化为材料物理性质的宏观变化。这些变化可以用简单的化学方法以模块化的方式完成。由此产生的材料可用于减声、防震涂层、个人防护设备（例如护齿器和多重冲击泡沫）和弹道防护。科学发现的进步将被纳入学生的教育和培训，整合广泛的学科，包括化学、物理、生物化学和聚合物科学。小组成员将从基础和应用的角度全面了解聚合物的合成，表征，形态，散射和流变性等许多领域。这种多学科的方法不仅有利于教育，而且有利于培养全面发展的毕业生，这些毕业生在学术和工业领域对各种雇主都有吸引力。在K-5小学科学推广的多样性和参与也被强烈强调。技术概述：本研究的目的是研究基于巯基网络（TEN）热固性吸能聚合物平台的基本材料特性。先前对TENs的研究表明，它能够通过化学手段进行分子水平的操纵，并将其转化为宏观性能和功能的变化。这项研究的目标是利用TEN改性的进展来合成新的单体，我们引入了增加韧性的机制，以及自我修复的潜力，最终将增加材料的使用寿命。这将用于板材（目标1）和泡沫（目标2）材料。在我们提出的研究中，我们将通过动态共价牺牲、机械化学键和加入光响应的液晶偶氮苯取代基来介绍这些分子水平的能量耗散和韧性机制。建立一个网络修改工具箱将使我们能够发现有潜力通过扩展功能来改变吸能材料领域的材料。本提案中开发的改良TEN材料平台是完全模块化的，可应用于个人防护设备、固化涂层、弹道防护、牙科修复材料和聚合物复合材料等应用。这项研究的成功完成将产生一个具有改进的冲击能量吸收特性的材料平台，以及对分子设计和操纵如何转化为动力学和宏观功能的理解。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。

NON-TECHNICAL SUMMARY:A unique property of polymers is their ability to absorb mechanical energy during impact events by transferring that energy into molecular motions of the individual polymer chains. This project is focused on studying the fundamental materials properties for a platform of energy-absorbing polymers and developing a toolbox to introduce molecular mechanisms to increase toughness, energy dissipation, and the potential for nanoscale self-healing that will increase the lifespan of the material. This platform is based on polymer network materials called "thiol-ene network thermosets". They can be made through chemistry that offers fast reaction times and highly homogeneous networks, like a chain-link fence, resulting in high energy absorption capacity. Previous work in the Savin group has demonstrated the ability to make molecular-level changes in the network and have this translate into macroscopic changes in the physical properties of the materials. These changes can be done in a modular way using facile chemistry. The resulting materials have applications in sound damping, shatterproof coatings, personal protective equipment (e.g., mouthguards and multi-impact foams), and ballistics protection. Advances in scientific discovery will be incorporated into the education and training of students, integrating a broad range of disciplines including chemistry, physics, biochemistry, and polymer science. Group members will gain a comprehensive understanding of polymers in many areas of synthesis, characterization, morphology, scattering and rheology, from both a fundamental and an applied standpoint. This multidisciplinary approach is beneficial not only for education, but also to produce well-rounded graduates who are attractive to a variety of employers in both academic and industrial settings. Diversity and involvement in K-5 elementary science outreach are also strongly emphasized. TECHNICAL SUMMARY:The objective of this research is to study the fundamental materials properties for a platform of energy absorbing polymers based on thiol-ene network (TEN) thermosets. Previous research on TENs has shown the ability to make molecular-level manipulations through chemistry and have this translate to changes in macroscopic performance and function. The goal of this research is to exploit advances in TEN modification to synthesize new monomers where we introduce mechanisms to increase toughness, as well as the potential for self-healing that will ultimately increase the life span of the material. This will be done for both slab (Aim 1) and foam (Aim 2) materials. In the proposed research, we will introduce these molecular-level mechanisms for energy dissipation and toughness through dynamic-covalent sacrificial, mechanochemical linkages, and incorporation of photo-responsive, liquid crystalline azobenzene substituents. Building a toolbox of network modifications will allow us to discover materials that have the potential to transform the field of energy-absorbing materials by expanding functionality. The modified TEN materials platform that will be developed in this proposal is completely modular and can be applied to applications such as personal protective equipment, curable coatings, ballistics protection, dental restoratives, and polymer composite materials. Successful completion of the proposed research will yield a platform of materials with improved impact-energy absorption properties, as well as an understanding of how molecular design and manipulation translates into dynamics and macroscopic function.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.