聚合物刷水润滑条件下水膜厚度和摩擦学行为的相关性研究

利用表面引发原子转移自由基聚合技术(SI-ARTP)在钢球和玻璃盘摩擦副表面分别接枝亲水性聚合物刷-聚甲基丙烯酸-3-磺酸丙酯钾盐(PSPMA)，去离子水作为润滑剂，在球-盘式摩擦试验机和纳米级薄膜厚度测量装置上开展了其宏观摩擦学性能研究，探讨了流体动压效应介入下的聚合物刷水润滑机理. 利用光干涉技术观察了低卷吸速度下(4 mm/s)接触区域水膜分布情况，发现滚道两侧水膜的形状由初始状态的圆形随着时间逐渐沿着卷吸方向分布，证实了聚合物刷通过不断捕获周围的水分子形成了1层稳定的水膜；通过控制卷吸速度从1 mm/s连续增加512 mm/s实现了润滑状态的转变，低卷吸速度时处于薄膜润滑状态，膜厚不依赖于速度且稳定在35 nm左右，接触区内有效水膜的建立归功于聚合物刷的水合效应；当速度大于32 mm/s时处于弹流润滑状态，膜厚的测量值高于等黏弹膜厚公式的预测值(2~12 nm)和水合效应促成的膜厚值(约35 nm)之和，这意味着在流体动压润滑作用下聚合物刷表现出了优异的润滑增强作用, 是水合效应和流体动压效应协同作用的结果. 

Correlation between Water Film Thickness and Tribological Behavior of Polymer Brush in Aqueous Lubrication

Research on macroscopic tribological performance of polymer brush was conducted on friction tester and nanoscale film thickness measuring device with ball-disc contact pairs, where steel balls and glass discs were grafted by hydrophilic polymer brush-polymethacrylic acid-3-sulfonic acid propyl potassium salt (PSPMA) respectively using surface-initiated atom radical transfer polymerization technology (SI-ARTP) and deionized water as a lubricant, the aqueous lubrication mechanism of polymer brush was explored under the intervention of hydrodynamic effect. Optical interferometry technique was used to observe actual distribution of water film in the contact area at low entrainment speed (4 mm/s), it was found that the shape of water film adjacent to both sides of raceway changed from a circular shape in the initial state to a distribution along entrainment speed direction with time, which confirmed that polymer brush formed a layer of stable aqueous film by continuously harvesting the surrounding water molecules. The transition of lubrication regime was achieved by controlling entrainment speed continuously increasing from 1 mm/s to 512 mm/s, it was considered to be in thin film lubrication regime at lower speed, where film thickness was independent of velocity and was stable at about 35 nm, and hydration effect of polymer brush was responsible for the establishment of effective film in contact; when velocity was greater than 32 mm/s, it transformed into elastic hydrodynamic lubrication, and the measured value of film thickness was higher than that of film thickness predicted by isoelastic film thickness formula (2~12 nm) added by film thickness due to hydration effect (~35 nm), which meant that polymer brush presented lubrication enhancement effect under hydrodynamic lubrication, which was resulted from synergistic effect of hydration effect and hydrodynamic effect.