不同分子结构聚酰亚胺固-液复合摩擦学行为与润滑机理研究

Solid-Liquid Duplex Lubrication Behavior and Mechanism of Polyimide with Different Molecular Structure

设计合成了一种新型热固性聚酰亚胺(TPI)材料,利用DMA242C型动态热机械分析仪、万能试验机以及接触角测量仪等对其机械性能、热学性能以及表面基础油PAO10的润湿性能进行表征,并与商业化的热塑性聚酰亚胺YS-20作对比,考察了两种不同分子结构的聚酰亚胺(PI)在PAO10润滑下的摩擦学行为.球-盘摩擦试验结果表明,无论是在模拟的多次“启-停”往复运动,还是模拟一次“启-停”的旋转接触运动,TPI与PAO10的固-液复合体系均具有优异的抗磨减摩性能,主要归因于TPI与PAO10之间较好的润湿性与物理吸附作用.通过分子动力学模拟的方法,进一步验证了空间化学交联TPI的空间化学交联结构增强了其表面与PAO10之间的物理吸附作用,有助于提高边界膜的构筑速度与承载能力,进而改善了两者复合体系的摩擦学行为.

With outstanding properties such as excellent mechanical performance,good thermal stability and chemical resistance,polyimide(PI)plays a vital role in many high-tech applications such as air-engines,aerospace vehicles,microelectronics industry and precision machinery.For a long-life lubrication in harsh condition,the recent creative methods combined self-lubricating PI with different base oil have come into practical application,such as porous oilimpregnated cage and oil-containing coating.In this article,a new type of thermosetting polyimide(TPI)material was synthesized and its mechanical properties,thermal properties and wetting behavior of surface base oil(PAO10)were characterized based on the technique of dynamic mechanical analysis(DMA),universal testing machine and contact angle measuring instrument,respectively.The commercial PI(YS-20)was also explored in comparison as different molecular structures of TPI.It was clear that TPI with the special structure of chemical crosslinking poses a higher heat-resistance and poor mechanical performance.Besides,the analysis of contact angle indicated that both TPI and YS-20 had a better wettability on the surface.In addition,the tribological behavior of the two PI with PAO10 solid-liquid duplex system was investigated to focus on the effect of tribological behavior of different PI molecular structures with PAO10 and mechanism of synergistic effect was further verified theoretically.On this basis,two modes of friction with ball-disk contact were used in order to reflect the varies of application condition.The continuous rotating mode would basically represent with a single“start-stop”and intermittent reciprocating motions could be on behalf of multiple“start-stop”to some extent.Compared with dry friction conditions,both TPI and YS-20 under oil lubrication showed extremely low friction coefficient and wear rate,while the system of TPI and PAO10 was better than YS-20 with PAO10.These results showed that the solid-liquid duplex system of TPI and PAO10 had excellent performance of antiwear,no matter in the simulation of multiple“start-stop”reciprocating motions or a single“start-stop”rotating contact.In contrast to YS-20,a further analysis demonstrated that the chemical crosslinking of TPI with a special benzene ring endows PI with a better wettability and rapid extension.Hence,we believe that the result of TPI-PAO10 with excellent friction-reducing and wear resistance might be attributed to the better wettability and physical adsorption between TPI and PAO10.Besides,the first-principles calculation about adsorption energy was also used to confirm our speculation between different PIs with PAO10 in this field.The result showed that TPI(ΔEadsorption=−32.30 kJ/mol)had a more positive adsorption with PAO10 than common structure of YS-20(ΔEadsorption=−20.92 kJ/mol).Through molecular dynamics simulation,it further verified that the TPI with special cross-linked structure enhances the physical adsorption between TPI surface and PAO10,which would be helpful to improve the construction speed and carrying capacity of the boundary film,thereby improving the composite system of tribological behavior.