Cihan Ebru, Heier John, Lubig Kevin, Gräf Stephan, Müller Frank A, Gnecco Enrico
Institute for Materials Science and Max Bergmann Center for Biomaterials, TU Dresden, 01069 Dresden, Germany.
Otto Schott Institute of Materials Research (OSIM), Friedrich Schiller University Jena, 07743 Jena, Germany.
ACS Appl Mater Interfaces. 2023 Mar 22;15(11):14970-14978. doi: 10.1021/acsami.3c00057. Epub 2023 Mar 7.
In this work, we investigated the sliding friction measured between poly(methyl methacrylate) (PMMA) colloidal probes with two different diameters (1.5 and 15 μm) and laser-induced periodic surface structures (LIPSS) on stainless steel with periodicities Λ of 0.42 and 0.9 μm, when the probes are elastically driven along two directions, perpendicular and parallel to the LIPSS. The time evolution of the friction shows the characteristic features of a reverse stick-slip mechanism recently reported on periodic gratings. The morphologies of colloidal probes and modified steel surfaces are geometrically convoluted in the atomic force microscopy (AFM) topographies simultaneously recorded with the friction measurements. The LIPSS periodicity is only revealed with smaller probes ( = 1.5 μm) and when Λ takes the largest value of 0.9 μm. The average value of the friction force is found to be proportional to the normal load, with a coefficient of friction μ varying between 0.23 and 0.54. The values of μ are rather independent of the direction of motion, and they reach their maximum when the small probe is scanned on the LIPSS with the larger periodicity. The friction is also found to decrease with increasing velocity in all cases, which is attributed to the corresponding decrease of the viscoelastic contact time. These results can be used to model the sliding contacts formed by a set of spherical asperities of different sizes driven on a rough solid surface.
在这项工作中，我们研究了直径分别为1.5μm和15μm的聚甲基丙烯酸甲酯（PMMA）胶体探针与周期Λ为0.42μm和0.9μm的不锈钢表面激光诱导周期性表面结构（LIPSS）之间的滑动摩擦力，其中探针沿垂直和平行于LIPSS的两个方向弹性驱动。摩擦力的时间演化显示出最近在周期性光栅上报道的反向粘滑机制的特征。在与摩擦力测量同时记录的原子力显微镜（AFM）形貌中，胶体探针和改性钢表面的形态在几何上相互交织。LIPSS周期性仅在较小的探针（ = 1.5μm）以及Λ取最大值0.9μm时才显现出来。发现摩擦力的平均值与法向载荷成正比，摩擦系数μ在0.23至0.54之间变化。μ的值相当独立于运动方向，并且当小探针在具有较大周期性的LIPSS上扫描时达到最大值。在所有情况下还发现摩擦力随速度增加而减小，这归因于粘弹性接触时间的相应减少。这些结果可用于模拟由在粗糙固体表面上驱动的一组不同尺寸的球形微凸体形成的滑动接触。
