Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , 205 North Matthews Avenue, Urbana, Illinois 61801, United States.
Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign , 1304 West Green Street, Urbana, Illinois 61801, United States.
Langmuir. 2018 Jan 23;34(3):756-765. doi: 10.1021/acs.langmuir.7b02834. Epub 2017 Oct 17.
The lubrication behavior of the hydrated biopolymers that constitute tissues in organisms differs from that outlined by the classical Stribeck curve, and studying hydrogel lubrication is a key pathway to understand the complexity of biolubrication. Here, we have investigated the frictional characteristics of polyacrylamide (PAAm) hydrogels with various acrylamide concentrations, exhibiting Young's moduli (E) that range from 1 to 40 kPa, as a function of applied normal load and sliding velocities by colloid probe lateral force microscopy. The speed-dependence of the friction force shows an initial decrease in friction with increasing velocity, while, above a transition velocity V*, friction increases with speed. This study reveals two different boundary lubrication mechanisms characterized by distinct scaling laws. An unprecedented and comprehensive study of the lateral force loops reveals intermittent friction or stick-slip above and below V*, with characteristics that depend on the hydrogel network, applied load, and sliding velocity. Our work thus provides insight into the closely tied parameters governing hydrogel lubrication mechanisms, and stick-slip friction.
构成生物体组织的水合生物聚合物的润滑行为不同于经典的 Stribeck 曲线所描述的行为，研究水凝胶的润滑是理解生物润滑复杂性的关键途径。在这里，我们通过胶体探针横向力显微镜研究了具有不同丙烯酰胺浓度的聚丙烯酰胺（PAAm）水凝胶的摩擦特性，其杨氏模量（E）范围从 1 到 40 kPa，作为施加的法向载荷和滑动速度的函数。摩擦力对速度的依赖性表现为摩擦力随速度的增加而初始减小，而在过渡速度 V* 以上，摩擦力随速度的增加而增加。这项研究揭示了两种不同的边界润滑机制，其特征是具有不同的标度定律。对横向力循环的前所未有的全面研究表明，在 V* 以上和以下存在间歇性摩擦或粘滑现象，其特征取决于水凝胶网络、施加的载荷和滑动速度。因此，我们的工作深入了解了控制水凝胶润滑机制和粘滑摩擦的紧密相关参数。
