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在机械部件表面形成保护膜。因此，对摩擦化学反应的基本了解可以导致开发更节能、更可持续的制造工艺。本研究课题处于化学工程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的培训。在剪切驱动化学反应的力学研究中，研究人员经常使用一个机械辅助的热激活模型，从该模型可以定义一个被称为临界活化体积的参数。最近实验技术的进步使得能够测量各种摩擦化学反应的活化量，并将测量值与各种物理体积进行了比较。然而，这种比较是没有根据的，因为热激活模型描述了反应的反应物和过渡态之间的能量差，并且不包含与这些状态相关联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，其大小取决于前体分子的几何结构、对滑动衬底的化学吸附或跨剪切面的界面键的形成，以及环境条件，如共吸附、温度、这一假设是通过补充摩擦化学实验和使用具有受控分子参数的模型系统的反应分子动力学模拟来研究的，该模型系统能够分离出个体对特定自变量集的贡献及其协同效应。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。

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.