基于声子和电子耗散的多层石墨烯摩擦机理研究

The energy dissipated by friction stands for about 40% of the total energy consumption in mechanical equipment. One third of the mechanical equipments lose function that are caused by wear due to the friction. It is believed that macroscopic friction is the sum of the frictional effects occurring at the atomic scale. However, the energy dissipation mechanism caused by friction is still not clear to date owing to the complex phenomena occurring at the buried interface of sliding surfaces. Based on its structure of large specific surface area and simple phonon mode, graphene is considered to be the ideal material for studying the mechanism of atomic scale friction energy dissipation. This project intends to (i) establish a supported multilayer graphene friction model based on molecular dynamics simulation method; (ii) investigate the relationship between friction, normal deformation energy, and corrugation potential, under different working condition parameters (such as temperature, sliding speed and commensurability, etc.); and (iii) expand the application scope of the Tomlinson model. Moreover, the phonon dissipation model of friction on the basis of a large number of simulation results will be constructed. Atomic force microscope (AFM) and surface force apparatus will be used to prove the validity of the established model. Additionally, in order to set up laws inherent to phonon and electronic contributions to friction, AFM measurements will be performed while a light beam is striking the samples to assure the electronic excitations. Electronic friction will be deduced from the total friction of graphene by varying the wavelength and intensity of the supplied light..This project aims at achieving a theoretical basis for active control friction, through investigating the friction energy dissipation mechanisms by theoretical modelling and experimental measurements.

摩擦耗能占机械设备总耗能的40%左右，摩擦导致的磨损是机械设备失效的主要形式之一。宏观摩擦被认为是原子尺度发生的摩擦效应总和，但由于摩擦副界面的复杂性，迄今，摩擦导致的能量耗散机理仍不清晰。石墨烯具有的大比表面积结构和简单的声子模态，为研究原子尺度的摩擦能耗机理提供了理想的研究对象。本项目拟采用分子动力学方法建立基底支撑的多层石墨烯摩擦力模型，研究不同工况参数（如温度、滑动速度、公度性等）下石墨烯摩擦力与法向变形能和界面褶皱势的依赖关系，拓展Tomlinson模型的应用范围；在大量仿真数据基础上，建立摩擦的声子耗散模型；采用原子力显微镜和表面力仪验证所建立模型的正确性；通过改变光波的波长和强度，控制石墨烯摩擦副在摩擦过程中电子耗散的比重，给出声子耗散和电子耗散对摩擦耗能的影响规律。.本项目拟通过理论建模和实验测量，研究摩擦耗能机理，为实现摩擦的主动控制奠定理论基础。

摩擦造成的机器零部件的磨损是机械设备失效的主要形式。据估计，全球约1/5的总能源因摩擦而损耗。然而，摩擦耗能的时空响应动力学过程仍不清晰。本项目基于分子动力学和量子力学等理论，结合原子力显微镜和拉曼光谱仪等实验仪器，对石墨烯等材料的摩擦行为进行了探究。具体如下：1）设计了基底弹性变形能和热激发效应的耦合作用对摩擦力贡献的摩擦系统，发现了摩擦力是由法向弹性变形能和界面褶皱势相竞争，以及热激发效应和滑移长度变化相竞争共同作用的结果，拓宽了Prandtl–Tomlinson摩擦模型的应用范围。2）建立了公度接触下支撑刚度梯度变化的石墨烯层间摩擦模型，分析了支撑刚度梯度变化时探针各接触区对摩擦耗能的贡献。提出了各接触区的摩擦力是探针和基底之间的褶皱势和接触区产生的法向变形差两部分的共同作用。3）计算了两接触石墨烯薄膜的界面原子力，阐释了从公度接触到非公度接触的摩擦演化进程。首次利用界面原子力分布呈现出超晶格结构摩尔纹，发现了接触应力形成的摩尔纹反映界面接触质量，而剪切应力形成的摩尔纹与摩擦力紧密相关。在公度和非公度接触状态，原子摩擦力均有一部分为正，另一部分为负，但相较于公度接触，在非公度接触时正原子摩擦力和负原子摩擦力的分布关于零点更对称，从而造成超低的有效摩擦合力。4）探究了石墨烯层间不同公度性接触状态下声子输运对摩擦耗能的影响。公度接触时产生摩擦耗能的原因是在相对滑动界面激发出了大量的LA和TA模式，这些新激发模式是摩擦能量的有效耗散通道。量化了被激发的各声学模式对摩擦力的贡献，为通过激励频率调控摩擦耗能提供理论指导。5）利用化学气相沉积法在二氧化硅基底上制备出二硫化钼和二硫化钨面内异质结实验样品，并就该异质结的摩擦磨损特性对法向载荷、滑动速度以及加载方式等工况参数的依赖关系进行探索。本项目的研究成果将为实现摩擦耗能的主动控制提供新的技术路线。