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

化学反应是许多制造工艺的基础，在其性能和能源利用方面发挥着重要作用。许多制造工艺涉及加热源材料以驱动反应以形成期望的产品。然而，驱动反作用力的另一种方式是通过使用机械力。该项目特别关注滑动界面摩擦力驱动的反应。这种摩擦化学反应支持包括化学机械抛光和在机械部件表面上形成保护膜的制造工艺。因此，对摩擦化学反应的基本理解可以导致开发更节能，可持续的制造工艺。该研究课题位于化学和机械工程的交叉点，因此，参与研究的学生必须接受跨学科培训。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，研究人员经常采用机械辅助热活化模型，从中可以定义称为"临界活化体积"的参数。实验技术的最新进展已经使得能够测量各种摩擦化学反应的活化体积，并且将测量值与各种物理体积进行了比较。然而，这样的比较是没有根据的，因为热活化模型描述了反应物和反应的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。这项工作假设活化体积由分子或表面原子在界面剪切下相对于其平衡几何形状变形的倾向决定，并且其大小由前体分子的几何结构、对滑动基底的化学吸附或跨剪切平面的界面键的形成以及环境条件如共吸附物、温度、该假设通过补充摩擦化学实验和反应分子动力学模拟进行研究，使用具有受控分子参数的模型系统，能够隔离个体对特定独立变量集及其协同效应的贡献。该奖项反映了NSF的法定使命，并被认为值得通过以下方式获得支持：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。

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.