Matsen M W
School of Mathematical and Physical Sciences, University of Reading, Whiteknights, Reading, UK.
Eur Phys J E Soft Matter. 2011 May;34(5):45. doi: 10.1140/epje/i2011-11045-4. Epub 2011 May 10.
This paper examines the normal force between two opposing polyelectrolyte brushes and the interpenetration of their chains that is responsible for sliding friction. It focuses on the special case of semi-dilute brushes in a salt-free theta solvent, for which Zhulina and Borisov (J. Chem. Phys. 107, 5952 (1997)) have derived analytical predictions using the classical strong-stretching theory (SST). Interestingly, SST predicts that the brushes contract as they are compressed together maintaining a polymer-free gap, which provides an explanation for the ultra-low frictional forces observed in experiment. We examine the degree to which the SST predictions are affected by chain fluctuations by employing self-consistent field theory (SCFT). While the normal force is relatively unaffected, fluctuations are found to have a strong impact on brush interpenetration. Even still, the contraction of the brushes does significantly prolong the onset of interpenetration, implying that a sizeable normal force can be achieved before the sliding friction becomes significant.
本文研究了两个相对的聚电解质刷之间的法向力以及它们的链相互穿透对滑动摩擦的影响。研究聚焦于在无盐θ溶剂中的半稀溶液刷这一特殊情况，对于此情况，朱利娜和鲍里索夫（《化学物理杂志》107, 5952 (1997)）已使用经典的强拉伸理论（SST）得出了分析预测。有趣的是，SST预测当刷子被压缩在一起时会收缩并保持一个无聚合物的间隙，这为实验中观察到的超低摩擦力提供了解释。我们通过采用自洽场理论（SCFT）来研究SST预测受链波动影响的程度。虽然法向力相对不受影响，但发现波动对刷子的相互穿透有强烈影响。即便如此，刷子的收缩确实显著延长了相互穿透的起始时间，这意味着在滑动摩擦变得显著之前可以实现相当大的法向力。
