芳基取代羧酸离子液体结构与摩擦学性能的构效关系研究

Relationship between Structure and Tribological Properties of Aryl-substituted Aromatic Acid Ionic Liquid Lubricants

目的研究芳基取代羧酸离子液体的分子结构与其摩擦学性能、物理化学性质之间的构效关系。方法分别以4-甲基苯乙酸(4-Me-PA)、4-叔丁基苯乙酸(4-tBu-PA)、4-苯基丁酸(PB)、异丁基苯丙酸钠(布洛芬钠,Ibu)作为阴离子源,以四丁基氢氧化铵(N4444OH)、四丁基氯化铵(N4444Cl)、1-丁基-3-甲基咪唑氯盐(C4mim)、1-辛基-3-甲基咪唑氯盐(C8mim)为阳离子源,通过酸碱中和反应和离子交换反应合成了七种芳基取代羧酸离子液体。以市售合成润滑油聚α-烯烃(PAO10)和传统离子液体1-丁基-3-甲基咪唑四氟硼酸盐(L-B104)为对照样,对其分子结构与摩擦学性能、物理化学性质之间的构效关系进行了系统研究。结果芳基取代羧酸离子液体的热分解温度在161~217℃之间,水解反应的p H值保持不变,具有较高的水解稳定性和热稳定性,对金属基底材料无腐蚀,作为润滑剂使用时,在钢/钢、钢/铜、钢/铝三种摩擦副上的平均摩擦系数f和平均磨损体积V分别为f钢/钢=0.081,f钢/铜=0.067,f钢/铝=0.080,V钢/钢=3.24×10-3 mm3,V钢/铜=22.04×10-3 mm3,V钢/铝=22.35×10-3 mm3,均具有良好的减摩抗磨性能,它们的分子结构对其摩擦学性能和物理化学性质均具有较明显的影响。结论芳基取代羧酸离子液体中,阳离子上取代烷基链越长,其热分解温度越高,运动黏度和黏度指数也越大;阴离子的空间体积越大,相应离子液体的黏度指数越大;它们在钢/钢、钢/铜、钢/铝摩擦副上均表现出良好的润滑作用。这主要是因为在摩擦过程中离子液体在摩擦副表面形成了稳定的吸附膜,在这层吸附膜中,阴阳离子的影响作用不同,阳离子对其减摩作用的影响较大,阴离子对其抗磨作用的影响较大;这层吸附膜的润滑性能还受到黏度的影响,具有适中运动黏度和较大黏度指数的离子液体作为润滑剂,摩擦学性能更加优异。

The work aims to study structure-function relationship between molecular structure and tribological/physico chemical properties of aryl-substituted aromatic acid ionic liquids（ILs）. With 4-methylphenylacetic acid（4-Me-PA）, 4-tert-butylphenylacetic acid（4-t Bu-PA）, 4-phenylbutyric acid（PB） and ibuprofen sodium salt（Ibu） as anion sources, and tetrabutylammonium hydroxide（N4444 OH）, tetrabutylammonium chloride（N4444 Cl）, 1-butyl-3-methylimidazolium chloride（C4 mim）, 1-octyl-3-methylimidazolium chloride（C8 mim） as cation sources, seven aryl-substituted aromatic acid ILs were synthesized based upon acid-base neutralization and ion exchange reaction. The structure-activity relationship between molecular structure and tribological/physicochemical properties of ILs was systematically investigated with commercially available synthetic poly-alpha-olefin（PAO 10） and 1-butyl-3-methylimidazolium tetrafluoroborate（L-B 104） as control samples. These ILs exhibited good hydrolysis stability, high thermal stability, and no corrosion to metallic substrates. Thermal decomposition temperature of the ILs ranged from 161 to 217 ℃, and p H value of hydrolysis reaction remained unchanged. Average friction coefficient f and average wear volume V of the three pairs was fsteel/steel=0.081, fsteel/copper=0.067, fsteel/aluminum=0.080, Vsteel/steel=3.24×10-3 mm3, Vsteel/copper=22.04×10-3 mm3, Vsteel/aluminum=22.35×10-3 mm3, respectively, when being applied to steel/steel, steel/copper and steel/aluminum friction pairs. These ILs had good anti-friction and anti-wear properties, and their molecular structure had significant effects on tribological/physicochemical properties. In the aryl-substituted aromatic acid ionic liquids, the longer the substituted alkyl chain is, the higher the thermal decomposition temperature is, the higher the kinematic viscosity and viscosity index are. The larger the space volume of anions is, the higher the viscosity index of corresponding ion liquids is. These ILs exhibited good lubrication on steel/steel, steel/copper, and steel/aluminum friction pairs, mainly owing to the formation of a stable adsorption film on the friction pairs. The anions and cations in the film have different effects, cations play a major role in reducing friction, while anions play a major role in resisting wear. The lubricating property is also affected by viscosity, the ILs with appropriate kinematic viscosity and high viscosity index exhibit more excellent tribological properties.