Chen Wenbin, Zhu Pengzhe, Liang He, Wang Wenzhong
School of Mechanical Engineering, Beijing Institute of Technology, Beijing 10081, PR China.
Langmuir. 2021 Feb 23;37(7):2426-2435. doi: 10.1021/acs.langmuir.0c03468. Epub 2021 Feb 9.
Porous polyimide (PI) materials are one of important bearing retainer materials in space applications due to the storage and continuous supply of a lubricant through the porous structure. Understanding the lubricant recycling process in porous polyimide retainers is of vital importance to improve lubricant supply performance of bearing. In this work, through molecular dynamic simulations, coarse-grained models are built to study lubricant recycling processes on porous and solid surfaces. A spontaneous imbibition behavior is observed when the lubricant is present on the porous surface. The dynamic change in the contact angle in this process and the deviation of the effective radius from the volumetric radius because of the molecular structure of polyimide causes the classical Lucas-Washburn (L-W) equation fail to describe the process. By fitting dynamic contact angle and effective radius, a modified L-W equation is developed, which well predicts the process of imbibition. Furthermore, it is found that the lubricants between the porous polyimide surface and the solid surface are recycled by extrusion, and spontaneous imbibition does not occur. In this case, the accumulation of lubricant pressure and weak interfacial interaction between the lubricant and the solid surface are also the main factors that promote lubricant recycling.
多孔聚酰亚胺（PI）材料因其能通过多孔结构储存并持续供应润滑剂，成为空间应用中重要的轴承保持架材料之一。了解多孔聚酰亚胺保持架中的润滑剂循环过程对于提高轴承的润滑剂供应性能至关重要。在这项工作中，通过分子动力学模拟，构建了粗粒度模型来研究多孔表面和固体表面上的润滑剂循环过程。当多孔表面存在润滑剂时，会观察到自发吸液行为。在此过程中接触角的动态变化以及由于聚酰亚胺分子结构导致的有效半径与体积半径的偏差，使得经典的卢卡斯 - 沃什伯恩（L - W）方程无法描述该过程。通过拟合动态接触角和有效半径，开发了一个修正的L - W方程，该方程能很好地预测吸液过程。此外，发现多孔聚酰亚胺表面与固体表面之间的润滑剂通过挤压进行循环，不会发生自发吸液。在这种情况下，润滑剂压力的积累以及润滑剂与固体表面之间较弱的界面相互作用也是促进润滑剂循环的主要因素。
