Impact of Wetting Transparency on Lubricating and Adhesive Properties of Two-Dimensional Materials

机油和润滑脂的润滑性能优化不佳导致摩擦增加，导致机器（如汽车发动机、风力涡轮机、轴承）的寄生能量损失，并且经常导致机器运行所需的单个部件逐渐磨损。相关的工业能源损失对环境和经济都有重大影响。二维（2D）材料已被单独使用，并作为油、润滑脂和其他基础润滑剂的添加剂，以改善其性能，而不是通过传统材料可以实现的。二维材料只有一个原子厚度，在其他两个方向上具有微米或更大的尺寸。该提案的目标是通过对二维材料覆盖的表面进行基本检查，进一步改进使用这些先进材料的润滑策略。为了确定二维材料减少摩擦和磨损的确切机制，需要进行这项基本检查。目前的缺点降低了2D材料的有效性，因此它们目前不适合实际应用，无论是在可靠性、使用寿命方面，还是在充分改善润滑性能方面。在本研究中，将通过超高真空原子力显微镜（UHV AFM）实验来实现二维材料的润滑机理。这些实验将揭示这些润滑油在没有环境或其他污染的情况下的真实性能。此外，将在特高压条件下确定的2D材料的润滑性能与实际条件进行比较，将揭示真正影响2D材料在工业应用中摩擦和减少磨损性能的环境因素。通过AFM实验获得的基本知识将用于改进描述滑动机械接触中的摩擦、磨损和其他能量损失机制的分析和物理模型。这些模型的改进对于低能机械系统的预测控制和设计至关重要。拟议的研究计划将使用AFM专门测量当这些润滑油覆盖表面的不同层数时表面能的变化。这些材料的固有厚度远远小于吸引力从表面延伸的距离。然而，在过去的几年里，环境污染的复杂性，在这种长度尺度上获取材料特性的困难，以及将计算机原子模拟与实验工作联系起来的挑战，导致了相互矛盾的发现。考虑到表面能的额外重要性，除了影响这些材料的润滑性能外，还影响复合材料、粘合材料和其他领域的混合，预计这项工作将在其他领域产生重大影响。

Poorly optimized lubrication properties of oils and greases results in increased friction causing parasitic energy losses in machines (such as automotive engines, wind turbines, bearings), as well as often resulting in the gradual wear of the individual components that are required for the machine to operate. The associated industrial energy losses have a significant impact on both the environment and the economy. Two-dimensional (2D) materials have been used on their own and as additives in oils, greases, and other base lubricants to improve their proeprties beyond what could be achieved through conventional materials. 2D materials are only one atom thick and have a micron or larger dimension in the other two directions. This proposal targets the further improvement of lubrication strategies using these advanced materials through fundamental examination of surfaces covered by 2D materials. This fundamental examination is required to determine the exact mechanisms by which 2D materials reduce friction and wear. This current shortcoming has reduced the effectiveness of 2D materials such that they are currently not suitable for real-world applications, be it in terms of reliability, life-times, or sufficiently improved lubrication properties. In this research, the lubricating mechanism of 2D materials will be achieved through experiments using ultra-high vacuum atomic force microscopy (UHV AFM). These experiments will reveal the true properties of these lubricants in the absence of environmental or other contamination. Further, a comparison of the lubricating properties of 2D materials determined under UHV conditions and real-world conditions will reveal the environmental factors that truly impact the friction and wear reducing properties of 2D materials in industrial applications. The fundamental knowledge gained through this AFM experimentation will be used to improve the analytical and physical models that describe friction, wear, and other energy-loss mechanisms in sliding mechanical contacts. The improvement of these models is critical for predictive control and design of low-energy mechanical systems. The proposed research program will use AFM to specifically measure changes in surface energy at the surface when varying numbers of layers of these lubricants cover the surface. The innate thinness of these materials is much smaller than the distance at which attractive adhesive forces typically extend from surfaces. However, complications with environmental contamination, the difficulty in accessing material properties at this length-scale, and challenges in linking computer atomistic simulations with experimental work has resulted in conflicting findings over the past years. Given the additional importance of surface energy, beyond impacting the lubricating properties of these materials, to mixing of composite materials, adhesive materials, and other fields, significant impact of this work in other fields is anticipated.