Lubrication mechanism of concentrated polymer brushes in solvents: effect of solvent viscosity
Lubrication mechanism of concentrated polymer brushes in solvents: effect of solvent viscosity
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DOI：
10.1039/c1py00215e
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发表时间：
2012-01-01
影响因子：
4.6
通讯作者：
Tsujii, Yoshinobu
中科院分区：
文献类型：
--
作者：
Nomura, Akihiro;Ohno, Kohji;Tsujii, Yoshinobu
我们研究了聚甲基丙烯酸甲酯 (PMMA) 浓缩聚合物刷 (CPB) 浸没在两种高粘度离子液体 (IL) 中的摩擦特性，这两种液体是 PMMA 的良好溶剂：N,N-二乙基-N-甲基-N-(2-甲氧基乙基)双(三氟甲磺酰基)亚胺铵 (DEME-TFSI) 和 1-乙基-3-甲基咪唑鎓双（三氟甲磺酰基）酰亚胺（EMI-TFSI）。这些离子液体可以将 PMMA 的 CPB 溶胀到与甲苯相同的程度，甲苯是一种更常用的粘度低得多的良溶剂。 PMMA 的 CPB 有效地减少了这些离子液体中表面之间的相互作用，从而形成了隐藏的流体动力润滑，其特征是摩擦系数 mu 与剪切速度 v 的依赖性。在流体动力润滑状态下，在双对数图中获得了它们之间的线性关系，在所研究的溶剂中给出了接近统一的斜率，这对于牛顿流体来说是预期的，即使粘度相差近两个数量级。更有趣的是，发现这种润滑状态下的 mu 值与溶剂的粘度成比例。这些结果不仅使我们能够详细讨论溶剂粘度对 CPB 系统润滑性能的影响，而且还证明了它们与 IL 作为润滑液结合使用时作为出色润滑系统的能力。
We investigated the frictional properties of concentrated polymer brushes (CPBs) of poly(methyl methacrylate) (PMMA) immersed in two highly viscous ionic liquids (ILs) that are good solvents for PMMA: N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMI-TFSI). These ILs could swell the CPB of PMMA to the same degree as toluene, a more commonly used good solvent of much lower viscosity. The CPB of PMMA effectively reduced the interaction between surfaces in these ILs and hence developed otherwise hidden hydrodynamic lubrication, which was characterized by the dependence of the frictional coefficient mu on shear velocity v. In the hydrodynamic-lubrication regime, the linear relationship was obtained between them in the double logarithmic plot, giving a slope close to unity, which is expected for a Newtonian fluid, in the solvents studied even though the viscosity differed by nearly two orders of magnitude. More interestingly, the mu values in this regime of lubrication were found to be scaled by the viscosity of the solvent. These results not only enable us to discuss the details of the effect of solvent viscosity on lubrication properties of the CPB systems but also demonstrated their ability to act as an excellent lubrication system in combination with ILs as lubricating fluids.