人类对于通过新材料和新方法来改善润滑，从而节约能源的探索从未停止过。超薄二维材料作为一种新材料，其摩擦学特性是当前的研究热点。然而，超薄二维材料在液体润滑剂，尤其是润滑油中的稳定分散问题并没有得到很好的解决，制约了超薄二维材料的实际应用。此外，超薄二维材料的横向尺寸，作为一个重要参数，对于其摩擦学特性的影响有待进一步研究。 针对上述问题，本文以多种尺寸的超薄二硫化钼和氧化石墨烯为研究对象，对其摩擦学特性展开研究。 首先，通过溶剂热法，一步完成超薄二硫化钼的合成与表面修饰，分别制备得到两种横向尺寸分别在纳米尺度和亚微米尺度且表面修饰有油胺分子的油溶性超薄二硫化钼。利用间接分散法将上述超薄二硫化钼成功分散到基础油中后，通过与其他含Mo元素添加剂的对比，发现纳米尺度超薄二硫化钼能大幅提高润滑油样品的极压性能，而亚微米尺度超薄二硫化钼则可以显著改善润滑油的摩擦磨损性能。 其次，通过直接对比上述两种横向尺寸不同的油溶性超薄二硫化钼以及微米尺度多层二硫化钼，发现超薄二硫化钼相较于多层二硫化钼，能够在更高的载荷下进入接触区并提供稳定润滑。并且发现油胺并不适合作为微米尺度多层二硫化钼的表面改性剂。而亚微米尺度超薄二硫化钼相较于纳米尺度超薄二硫化钼具有更好的摩擦磨损性能，说明横向尺寸对超薄二维材料的摩擦学特性会产生影响。 然后，为了进一步深入研究横向尺寸对超薄二维材料摩擦学特性的影响规律，选取三种横向尺寸不同的氧化石墨烯分别分散到去离子水中，研究其水溶液在不同质量分数下的摩擦磨损性能。发现相同质量分数下，含有较大尺寸氧化石墨烯的水溶液能取得更低的摩擦系数和磨损量。从而得到了超薄二维材料横向尺寸对其摩擦学特性影响的一般规律。 最后，在发现并研究丙三醇水溶液超润滑的基础上，研究了氧化石墨烯对其超润滑特性的影响。发现添加氧化石墨烯能够在保持超低摩擦系数的同时，大幅缩短跑合时间、减小磨斑面积并且降低磨斑区域表面粗糙度，从而在更高压强下实现稳定超润滑。

The pursuing of saving energy via improving lubrication through new materials and new methods has never stopped. The ultrathin two-dimensional material is a kind of novel material and the investigation of its tribological properties is one of the research hotspots. However, the stable dispersion of ultrathin two-dimensional materials in liquid lubricants, especially in lubricant oils, has not been well achieved, which hinders the practical use of the ultrathin two-dimensional material. Moreover, the lateral size of the ultrathin two-dimensional material is a very important factor, but its influence on the tribological properties has rarely been focused on and needs further research. In this thesis, the tribological properties of multi-size ultrathin MoS2 and graphene oxide (GO) are mainly studied. Firstly, two kinds of oil-soluble ultrathin MoS2, which are both surface-modified with oleylamine (OAm) molecules and whose lateral size are at nano-scale and submicro-scale respecitively, are prepared through solvothermal metheds. In these methods, the synthesis and surface modification of the MoS2 are finished in one step. After the two kinds of ultrathin MoS2 are succesfully dispersed into base oil through an indirect despersion method, they are compared with other Mo-contained lubricant additives. It is found that the nano-scale ultrathin MoS2 can largely improve the extreme pressure property of the lubricant and the submicro-scale ultrathin MoS2 is able to greatly enhance the friction and wear properties of the lubricant. Secondly, by directly comparing the two kinds of synthetic ultrathin MoS2 and micro-scale multilayer MoS2, it is found that the ultrathin MoS2 can enter the contact area and provide stable lubrication under higher load. And OAm helps little in improving the tribological preperties and dispersibility of the micro-scale multilayer MoS2. Furthermore, it is found that the submicro-scale ultrathin MoS2 has better tribological properties than nano-scale ultrathin MoS2, indicating that the lateral size of the ultrathin two-dimensional material has an impact on the tribological properties. Then, with the order to further investigate the influence of the lateral size on the tribological properties of ultrathin two-dimensional materials, three kinds of GO with different lateral size are dispersed in deionized water forming GO solution with various weight fraction. It is found that when the weight fraction of GO in the solution is the same, the solution containing larger GO sheets is of better friction and wear properties. Thus the general rule of the effect of the lateral size on the tribological properties of ultrathin two-dimensional materials is discovered. Finally, based on the discovery and investigation of the superlubricity of glycerol solution, the impact of GO on the superlubricity is researched. It is found that, after adding GO into glycerol solution, not only the ultralow coefficient of fricrion is maintained, but also the running-in period is shorten, the wear scar size is decreased and the wear scar surface becomes smoother. Therefore, stable superlubricity can be achieved under higher pressure with the addition of GO.