Collaborative Research: Mechanistic Understanding of Chemical Activation in Shear-Driven Manufacturing Processes

化学反应是许多制造过程的基础，对其性能和能源利用起着重要作用。许多制造过程涉及加热源材料，以驱动反应形成所需的产品。然而，另一种驱动反应的方法是通过使用机械力。这个项目特别关注滑动界面上由摩擦力驱动的反应。这种摩擦化学反应是制造过程的基础，包括化学机械抛光和机械部件表面保护膜的形成。因此，对摩擦化学反应的基本理解可以导致更节能，可持续的制造工艺的发展。本研究课题是化学工程与机械工程的交叉学科，因此，参与研究的学生必须接受跨学科的训练。这项研究被整合到本科和研究生课程中，并吸引了来自代表性不足群体的学生。在剪切驱动化学反应的机理研究中，研究人员通常采用机械辅助热活化模型，从中可以定义一个被称为“临界活化体积”的参数。实验技术的最新进展已经能够测量各种摩擦化学反应的活化体积，并将测量值与各种物理体积进行比较。然而，这种比较是没有根据的，因为热活化模型描述了反应物和反应过渡态之间的能量差，并且不包含与这些状态相关的分子描述的分子信息。这项工作假设激活体积是由分子或表面原子在界面剪切作用下相对于其平衡几何形状的变形倾向决定的，其大小由前体分子的几何结构、对滑动基底的化学吸附或在剪切平面上形成界面键以及环境条件（如共吸附、温度等）决定。这一假设是通过互补的摩擦化学实验和反应性分子动力学模拟来研究的，使用具有控制分子参数的模型系统，可以分离出对特定自变量集的个体贡献及其协同效应。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。

Chemical reactions are the basis of many manufacturing processes and play important roles in their performance and energy utilization. Many manufacturing processes involve heating source materials to drive reactions to form desired products. However, another way to drive reactions is through the use of mechanical force. This project focuses specifically on reactions driven by friction force at sliding interfaces. Such tribochemical reactions underpin manufacturing processes including chemical mechanical polishing and the formation of protective films on the surface of mechanical components. As such, a fundamental understanding of tribochemical reactions can lead to the development of more energy efficient, sustainable manufacturing processes. This research topic lies at the intersection of chemical and mechanical engineering and, as such, the students involved in the research necessarily receive interdisciplinary training. This research is integrated into undergraduate and graduate courses and engages students from underrepresented groups.In mechanistic studies of shear-driven chemical reactions, researchers often employ a mechanically assisted thermal activation model from which a parameter referred to as the ‘critical activation volume’ can be defined. Recent advancements in experimental techniques have enabled measurement of this activation volume for various tribochemical reactions and the measured values have been compared with a variety of physical volumes. However, such comparisons are unfounded since the thermal activation model describes an energy difference between the reactant and transition states of a reaction and does not contain molecular information of a molecular description associated with these states. This work hypothesizes that activation volume is determined by the propensity of molecules or surface atoms to deform relative to their equilibrium geometries under interfacial shear, and that its magnitude is governed by the geometric structure of precursor molecules, chemisorption to the sliding substrate or formation of interfacial bonds across a shear plane, and environmental conditions such as co-adsorbates, temperature, etc. This hypothesis is investigated through complementary tribochemical experiments and reactive molecular dynamics simulations using model systems with controlled molecular parameters that enable isolation of the individual contributions to the specific set of independent variables and their synergistic effects.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.