胆固醇衍生离子液体复合氮化硼纳米片作为减摩抗磨添加剂的性能研究

Performance of Cholesterol-Derived Ionic Liquid Composite Boron Nitride Nanosheets as Anti-Friction and Anti-Wear Additives

本文中以天然胆固醇为前体,合成了一种胆固醇基胍盐离子液体[ColC_(4)][TMG],并通过机械-化学剥离法获得了纳米尺寸的六方氮化硼纳米片(h-BNNS),通过NMR、HRMS、TEM、FT-IR和XRD等表征了离子液体(IL)和hBNNS的结构特征.将其单独或复合后作为基础油(PEG 200)的减摩抗磨添加剂,通过球-盘往复摩擦形式,考察高载荷下(200 N)作为钢/钢摩擦副间润滑剂的摩擦学性能,结果表明,使用离子液体复合氮化硼纳米片(IL@BNNS)作为添加剂时,表现出最优的减摩抗磨性能,摩擦系数和磨损体积分别降低67%和77%,最优添加质量百分浓度为1.5%IL和0.1%的BNNS.通过分析磨斑形貌和表面元素化学组成,IL@BNNS的协同减摩抗磨机理主要归结为极性离子液体通过静电作用和分子间相互作用吸附在金属基底表面形成厚而致密的润滑膜,降低了液体分子间的剪切作用,同时IL与基底发生摩擦化学反应形成摩擦膜,阻止基底的进一步磨损.而h-BNNS在摩擦过程中进入接触区域,利用层间弱相互作用发生滑移,并抛光和自修复磨斑表面,使磨斑表面平整光滑,从而进一步降低磨损.

With the elevation of environmental awareness and the implementation of sustainable development strategies,more new requirements have been proposed for the development of the lubricants,and green,environmental compatible lubricants or lubricant additives present a promising requirement.In recent years,renewable lubricating products derived from biomass have huge application potential in replacement of petroleum-based products.A variety of lubricating products with natural products as raw materials have been established in part of the industrial applications.However,these bio-based lubricating products have some shortcomings,such as difficulty in preparation,poor compatibility,high cost,and particularly poor performance.Therefore,some two-dimensional nanomaterials are usually used to enhance and coordinate the performance of bio-lubricants.In order to harmonize both enhanced tribological properties and renewable abilities of lubricant,huge efforts have been paid to develop the new lubrication system and reveal the internal mechanism of action.In this study,a cholesteryl-guanidine salt ionic liquid(IL)denoted as[ColC_(4)][TMG]was designed and synthesized with natural renewable cholesterol as a precursor by proton transfer reaction,with cholesterol derivative as anion and tetramethylguanidine(TMG)as cation.As well as nano-sized hexagonal boron nitride nanosheets(h-BNNS)as friction modifier additives were prepared by mechano-chemical peeling method.The structural characteristics of synthesized IL were characterized by nuclear magnetic resonance,high resolution mass spectrometry,and Fourier transform infrared spectroscopy.The structures of the prepared BNNS were confirmed by transmission electron microscope and X-ray diffraction.They were used alone or in combination as the friction reduction and anti-wear additives in PEG 200 with different concentrations.The viscosity and thermal stability of lubricant samples were analyzed by stabinger viscometer and simultaneous thermogravimetry.Their lubrication performance for steel/steel friction pairs at 25℃was evaluated and compared by multifunctional friction tester with a ball-on-disc reciprocating configuration.The morphology and element state of worn scars were analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy to investigate the evolution of wear and tribochemical reactions.By combining the above results,the lubrication mechanism of IL compound BNNS as an additive was explored.The results showed that it was feasible that with cholesterol as a precursor,short-chain carboxylic acid was first introduced to cholesterol skeleton through esterification reaction,and then functional IL could be prepared through proton transfer reactions with amines.And BNNS with a size of about 70~80 nm was successfully prepared to improve the dispersion of nano-additives.The lattice distance of BNNS between adjacent fringes was about 0.25 nm,corresponding to 100 crystal planes of BN crystal,which proved that the crystal structure of BN was not destroyed during the mechano-chemical peeling treatment.It was obvious that IL composited BNNS(IL@BNNS)as an additive showed better dispersion stability compared with a single BNNS additive in basic oil,which was attributed to the branching of the alkyl chain of the IL to the oxidation bond on the BNNS surface.