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.

中文翻译：

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轴承多孔聚酰亚胺保持架中润滑剂循环的分子动力学模拟

多孔聚酰亚胺（PI）材料是空间应用中重要的轴承保持器材料之一，因为通过多孔结构存储和连续供应润滑剂。了解多孔聚酰亚胺保持架中的润滑剂再循环过程对于改善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，建立了粗颗粒模型来研究多孔和固体表面上的润滑剂循环过程。当润滑剂存在于多孔表面上时，观察到自发的吸收行为。由于聚酰亚胺的分子结构，在此过程中接触角的动态变化以及有效半径与体积半径的偏差导致经典的Lucas-Washburn（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LW方程，该方程很好地预测了吸水过程。此外，发现多孔聚酰亚胺表面和固体表面之间的润滑剂通过挤出而再循环，并且不会自发吸收。在这种情况下，润滑剂压力的累积以及润滑剂与固体表面之间的弱界面相互作用也是促进润滑剂再循环的主要因素。