Singh Manjesh K, Ilg Patrick, Espinosa-Marzal Rosa M, Kröger Martin, Spencer Nicholas D
§School of Mathematical and Physical Sciences, University of Reading, Reading RG6 6AX, United Kingdom.
∥Laboratory for Smart Interfaces in Environmental Nanotechnology, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Champaign, Illinois 61801, United States.
Langmuir. 2015 Apr 28;31(16):4798-805. doi: 10.1021/acs.langmuir.5b00641. Epub 2015 Apr 16.
Surfaces coated with polymer brushes in a good solvent are known to exhibit excellent tribological properties. We have performed coarse-grained equilibrium and nonequilibrium molecular dynamics (MD) simulations to investigate dextran polymer brushes in an aqueous environment in molecular detail. In a first step, we determined simulation parameters and units by matching experimental results for a single dextran chain. Analyzing this model when applied to a multichain system, density profiles of end-tethered polymer brushes obtained from equilibrium MD simulations compare very well with expectations based on self-consistent field theory. Simulation results were further validated against and correlated with available experimental results. The simulated compression curves (normal force as a function of surface separation) compare successfully with results obtained with a surface forces apparatus. Shear stress (friction) obtained via nonequilibrium MD is contrasted with nanoscale friction studies employing colloidal-probe lateral force microscopy. We find good agreement in the hydrodynamic regime and explain the observed leveling-off of the friction forces in the boundary regime by means of an effective polymer-wall attraction.
众所周知，在良溶剂中涂覆有聚合物刷的表面具有优异的摩擦学性能。我们进行了粗粒度平衡和非平衡分子动力学（MD）模拟，以从分子细节上研究水性环境中的葡聚糖聚合物刷。第一步，我们通过匹配单个葡聚糖链的实验结果来确定模拟参数和单位。将该模型应用于多链系统时，从平衡MD模拟获得的末端连接聚合物刷的密度分布与基于自洽场理论的预期结果非常吻合。模拟结果进一步与现有实验结果进行了验证和关联。模拟的压缩曲线（法向力作为表面间距的函数）与使用表面力装置获得的结果成功对比。通过非平衡MD获得的剪切应力（摩擦力）与采用胶体探针侧向力显微镜的纳米级摩擦研究结果形成对比。我们发现在流体动力学区域有很好的一致性，并通过有效的聚合物-壁吸引力解释了在边界区域观察到的摩擦力趋于平稳的现象。
