Lorenz Matthias, Pawlicki Alison A, Hysmith Holland E, Cogen Kerry, Thaker Hitesh, Ovchinnikova Olga S
Center for Environmental Biotechnology, University of Tennessee, Knoxville, 1416 Circle Drive, Knoxville, Tennessee 37996, United States.
Bredesen Center for Interdisciplinary Research, University of Tennessee, Knoxville, 821 Volunteer Blvd., Knoxville, Tennessee 37996, United States.
ACS Appl Mater Interfaces. 2022 Aug 3;14(30):35157-35166. doi: 10.1021/acsami.1c16761. Epub 2022 Jul 21.
Understanding the mechanism of antiwear (AW) tribofilm formation and how to tune surface chemistry to control functionality is essential for the development of the next generation of oil lubricants. In particular, understanding and optimizing early AW tribofilm formation can increase the energy efficiency of mechanical systems. However, the mechanism for how these films form is not well understood. The majority of prior work has focused on analyzing only end-of-test surfaces long after the film has formed. In this work, we develop an multimodal chemical imaging methodology to directly visualize the early formation of AW films on steel surfaces. We investigate an oil formulation containing a phosphorus-based additive commonly used to protect surfaces from wear and fatigue processes in machine elements, such as gears, bearings, and sliding contacts. Using nanoscale multimodal chemical imaging on combined platforms of atomic force microscopy (AFM) coupled directly with nano-infrared (nano-IR) spectroscopy, and further combined with time-of-flight secondary ion mass spectrometry (ToF-SIMS), we demonstrate a direct correlation between changes in friction and local surface chemistry. In these experiments, the AFM probe acts as a single asperity contact to generate the tribofilm as well as a tool to analyze it as it is forming. To verify our measurements, we compare these results to the ToF-SIMS of macroscale block-on-ring tribometer-formed samples. The understanding gained here on how AW films form and how film properties can be modified by tuning the chemistry of the additives will facilitate developing transmission fluids to meet increasing demands for vehicle performance and efficiency.
了解抗磨（AW）摩擦膜的形成机制以及如何调整表面化学性质以控制其功能，对于下一代润滑油的开发至关重要。特别是，了解并优化早期AW摩擦膜的形成可以提高机械系统的能源效率。然而，这些膜的形成机制尚未得到很好的理解。大多数先前的工作仅专注于在膜形成很久之后分析测试结束时的表面。在这项工作中，我们开发了一种多模态化学成像方法，以直接观察钢表面上AW膜的早期形成。我们研究了一种含有磷基添加剂的油配方，该添加剂通常用于保护机器部件（如齿轮、轴承和滑动接触）的表面免受磨损和疲劳过程的影响。通过在原子力显微镜（AFM）与纳米红外（nano-IR）光谱直接耦合的组合平台上进行纳米级多模态化学成像，并进一步与飞行时间二次离子质谱（ToF-SIMS）相结合，我们证明了摩擦变化与局部表面化学之间的直接相关性。在这些实验中，AFM探针既作为单个微凸体接触来生成摩擦膜，又作为在其形成过程中对其进行分析的工具。为了验证我们的测量结果，我们将这些结果与宏观尺度环块摩擦磨损试验机形成的样品的ToF-SIMS结果进行了比较。在此获得的关于AW膜如何形成以及如何通过调整添加剂的化学性质来改变膜性能的理解，将有助于开发传动液以满足对车辆性能和效率不断增长的需求。
