Su Liangliang, Krim Jacqueline, Brenner Donald W
Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, United States.
Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States.
ACS Omega. 2020 Apr 27;5(18):10349-10358. doi: 10.1021/acsomega.0c00073. eCollection 2020 May 12.
The dynamics of cubo-octahedral nanodiamonds (NDs) with three different surface treatments and confined in aqueous environments between gold surfaces under shear and normal loading conditions have been characterized via molecular dynamics (MD) simulations. The treatments consisted of carboxyl (-COO) or amino (-NH ) groups attached to the NDs, producing either negatively or positively charged NDs, respectively, and hydrogen-terminated surfaces producing neutral NDs. Simulations were performed in the presence and absence of induced image charges to explore the impact of electrostatic interactions on friction and surface deformation. Significant deformation of the gold surfaces was observed for negatively charged NDs placed between gold surfaces under external loads that were sufficient to displace water from the contact. Rolling and relatively high friction levels were also observed for the negatively charged NDs under the same conditions. In contrast, the neutral and positively charged NDs exhibited sliding behavior with only minor deformation of the gold surfaces. The results suggest that the size of the surface functional group plays a major role in determining whether NDs slide or roll on solid contacts. Higher friction levels were also observed in conjunction with induced image charges in the gold contacts. The results demonstrate how surface functionalization and surface-induced charges can work in combination to profoundly influence tribological performance.
通过分子动力学（MD）模拟，对三种不同表面处理且在剪切和法向加载条件下限制在金表面之间的水环境中的立方八面体纳米金刚石（NDs）的动力学进行了表征。处理方式包括在NDs上连接羧基（-COO）或氨基（-NH ）基团，分别产生带负电或正电的NDs，以及氢终止表面产生中性NDs。在有和没有感应镜像电荷的情况下进行模拟，以探索静电相互作用对摩擦和表面变形的影响。对于置于金表面之间的带负电的NDs，在足以使水从接触处排出的外部载荷下，观察到金表面有明显变形。在相同条件下，带负电的NDs也观察到滚动和相对较高的摩擦水平。相比之下，中性和带正电的NDs表现出滑动行为，金表面仅有轻微变形。结果表明，表面官能团的大小在决定NDs在固体接触上是滑动还是滚动方面起主要作用。在金接触中有感应镜像电荷时也观察到较高的摩擦水平。结果表明表面功能化和表面感应电荷如何共同作用以深刻影响摩擦学性能。
