Unraveling Mechanics of High Strength and Low Stiffness in Polymer Nanocomposites through Integrated Molecular Modeling and Nanomechanical Experiments

材料中弹性应变能的存储和释放以及机械强度在自然和工程机械驱动系统中都起着重要的作用，例如负责动物快速和高功率运动的生物组织。回弹模数提供了对一种材料吸收和释放弹性应变能的能力的测量--S吸收和释放弹性应变能的能力，由这些材料的强度和刚度之比决定。一般来说，设计弹性模数是非常困难的，因为它需要不对称地增加强度和刚度，而不是它们之间的相互缩放行为。作为另一种途径，该奖项支持基础研究，以阐明如何使用纳米颗粒来调整其聚合物复合材料的机械行为，以同时实现高强度和低刚性。这些知识将加速设计高强度、但符合要求的聚合物材料，用于广泛的应用，如轻质弹性储能装置、保护性涂层、柔性和可折叠光电子学以及人造肌肉。因此，这项研究不仅将促进科学的进步，而且将促进国民的健康、繁荣和福祉。它还可以通过技术创新来帮助确保国防安全，例如飞机的轻型能量吸收和保护系统。通过整合多个学科，该项目将为下一代劳动力发展培养材料力学、聚合物科学、机械工程和材料科学与工程领域的不同群体的学生。该项目的教育目标将通过课程开发、本科生研究机会、高中生暑期研究计划、K-12教师研究经验计划和K-12推广计划来实现。将作出特别努力，让代表人数不足的学生参与这一项目。本项目的目的是验证这样一种假设，即高强度和低刚度的结合归因于含有球形纳米粒子的聚合物纳米复合材料的独特微观结构，该复合材料含有球形纳米粒子与软聚合物基质弱相互作用。为了实现这一目标，研究计划包括两个主要目标。目标1的目标是建立一个集多尺度分子模拟和互补纳米力学实验于一体的研究框架，用于研究高强度、低刚度的聚合物纳米复合材料。它将被用来阐明与聚合物基质的自由体积元素相比，纳米颗粒的尺寸如何影响聚合物纳米复合材料的力学行为。在目标2中，将推广实现高强度和低刚度相结合的托换力学原理，以指导新型聚合物纳米复合材料的探索。这些具有超高弹性储能能力的纳米复合材料可用于卓越的机械保护、人造肌肉、软机器人和柔性电子产品。这一跨学科的努力将为定量理解异常的高强度和低刚度行为开辟有希望的途径，并为一类新型纳米复合材料的设计原理提供机械见解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The storage and release of elastic strain energy in materials, along with mechanical strength, play important roles in both natural and engineered mechanical actuation systems, such as biological tissues responsible for the fast and high-powered locomotions in animals. The modulus of resilience provides the measure of a material?s ability to absorb and release elastic strain energy, determined by the ratio between strength and stiffness of these materials. In general, engineering the modulus of resilience is extremely difficult because it requires asymmetrically increasing strength and stiffness against their mutual scaling behavior. As an alternative route, this award supports fundamental research to elucidate how nanoparticles can be used to tune mechanical behaviors of their polymer composites for simultaneously achieving high strength and low stiffness. This knowledge will accelerate the design of high strength, yet compliant polymeric materials for a broad range of applications, such as light-weight elastic energy storage devices, protective coatings, flexible and foldable optoelectronics, and artificial muscles. Thus, this research will not only promote the progress of science, but also advance the national health, prosperity and welfare. It can also help to secure national defense through technological innovations, e.g. light-weight energy absorption and protection systems for aircrafts. By integrating multiple disciplines, this project will train a diverse group of students in the areas of mechanics of materials, polymer science, mechanical engineering, and material science and engineering for next-generation workforce development. The educational objectives of the project will be realized through curriculum development, undergraduate research opportunities, summer research program for high school students, research experience for K-12 teachers program, and K-12 outreach program. Special efforts will be made to involve underrepresented students in this project. The objective of this project is to test the hypothesis that the combination of high strength and low stiffness is attributed to the unique microstructure of polymer nanocomposites that contains spherical nanoparticles weakly interacting with soft polymer matrix. To achieve this objective, the research plan consists of two major aims. The goal of Aim 1 is to establish a research framework integrating multiscale molecular modeling and complementary nanomechanical experiments for studying polymer nanocomposites with high strength and low stiffness. It will be used to elucidate how the size of nanoparticles, in comparison with free volume elements of the polymer matrix, can influence mechanical behaviors of polymer nanocomposites. In Aim 2, the underpinning mechanics principle of attaining the combination of high strength and low stiffness will be generalized to guide exploration of a novel class of polymer nanocomposites. These nanocomposites with ultra-high elastic energy storage capability can be used for superior mechanical protection, artificial muscles, soft robotics and flexible electronics. The interdisciplinary effort will open promising avenues for quantitatively understanding the anomalous high strength and low stiffness behaviors, and offer mechanistic insights into the design principles of a novel class of nanocomposites.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.