Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States.
Langmuir. 2011 Jun 7;27(11):6808-13. doi: 10.1021/la2002699. Epub 2011 May 2.
The nanoscale spreading of a cationic polymer lubricant (CPL) film consisting of polydimethylsiloxane with quaternary ammonium salt side chains on a SiO(2) surface was studied with the disjoining pressure measurements using atomic force microscopy. CPL shows a monotonic decrease in disjoining pressure as the film thickness increases from 1.3 to 4.5 nm, which suggests stable spreading in this thickness range. Comparing the spreading rates calculated from disjoining pressure and the viscosity of CLP to the self-healing time after tribo-contacts revealed that the ionic form may not be the main mobile species. The X-ray photoelectron spectroscopy analysis found that the CPL film on SiO(2) has about 30% of the quaternary ammonium salts (cationic groups) reduced to tertiary amines (neutral groups). The reduced CPL polymer has much lower viscosity than the original CPL polymer and yields a spreading rate consistent with that measured at the macroscale. Thus, the mobile component in the CPL/SiO(2) film responsible for self-healing is concluded to be the reduced tertiary amine components of CPL.
采用原子力显微镜的不结合压力测量法研究了由带有季铵盐侧链的聚二甲基硅氧烷组成的阳离子聚合物润滑剂（CPL）在二氧化硅（SiO2）表面上的纳米级铺展情况。CPL 显示出随着膜厚从 1.3nm 增加到 4.5nm，不结合压力呈单调下降的趋势，这表明在这个厚度范围内具有稳定的铺展性。将从不结合压力和 CLP 的粘度计算得出的铺展速率与摩擦接触后的自修复时间进行比较表明，离子形式可能不是主要的移动物种。X 射线光电子能谱分析发现，SiO2 上的 CPL 膜有约 30%的季铵盐（阳离子基团）还原为叔胺（中性基团）。还原后的 CPL 聚合物的粘度比原始 CPL 聚合物低得多，其铺展速率与在宏观尺度上测量的速率一致。因此，CPL/SiO2 薄膜中负责自修复的可移动成分被认为是 CPL 的还原叔胺成分。
