State Key Laboratory of Tribology, Tsinghua University, Beijing, China.
Langmuir. 2012 Nov 13;28(45):15816-23. doi: 10.1021/la303897x. Epub 2012 Nov 1.
Friction behavior of aqueous solution at macroscale is quite different from that at nanoscale. At macroscale, tribochemistry usually occurs between lubricant and friction surfaces in the running-in process due to a high contact pressure, and most such processes can lead to friction reduction. In the present work, we reported that the hydrogen ions in aqueous solution played an important role in tribochemistry in running-in process (friction reducing process), which could result in the friction coefficient reducing from 0.4 to 0.04 between Si(3)N(4) and glass surfaces at macroscale. It is found that the running-in process and low friction state are closely dependent on the concentration of hydrogen ions in the contact region between the two friction surfaces. The lubrication mechanism is attributed to tribochemical reaction occurring between hydrogen ions and surfaces in the running-in process, which forms an electrical double layer and hydration layer to lower friction force. Finally, the running-in process of H(3)PO(4) (pH = 1.5) was investigated, which could realize superlubricity with an ultralow friction coefficient of about 0.004.
在宏观尺度上，水溶液的摩擦行为与纳米尺度上的摩擦行为有很大的不同。在宏观尺度上，由于接触压力高，摩擦副之间的摩擦副通常会在磨合过程中发生摩擦化学作用，而大多数此类过程都能降低摩擦。在本工作中，我们报道了水溶液中的氢离子在磨合过程（减摩过程）中在摩擦化学中起着重要作用，这可以导致宏观尺度上 Si(3)N(4)和玻璃表面之间的摩擦系数从 0.4 降低到 0.04。研究发现，磨合过程和低摩擦状态与两个摩擦表面之间接触区域中氢离子的浓度密切相关。这种润滑机制归因于磨合过程中氢离子与表面之间发生的摩擦化学反应，它形成了双电层和水化层，从而降低了摩擦力。最后，研究了 H(3)PO(4)（pH = 1.5）的磨合过程，其可以实现超低摩擦系数约为 0.004 的超滑。
