Priority Research Centre for Advanced Fluids and Interfaces, The University of Newcastle, Callaghan, NSW 2308, Australia.
School of Chemical Science and Engineering, KTH Royal Institute of Technology, SE100 44 Sweden and Chemistry, Materials and Surfaces, SP Technical Research Institute of Sweden, SE114 86 Sweden.
Faraday Discuss. 2017 Jul 1;199:311-322. doi: 10.1039/c6fd00236f. Epub 2017 Apr 19.
Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl)amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI anion rich boundary layer at positive potentials is more lubricating than the Li cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li cations for both surfaces at negative potentials. However, at Au(111), the TFSI rich boundary layer is less lubricating than the Li rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO rich boundary layer.
原子力显微镜（AFM）已被用于研究溶剂化离子液体（SIL）-高取向热解石墨（HOPG）和 SIL-Au（111）界面上的电位依赖边界层摩擦。在 HOPG 上，四甘醇双（三氟甲基磺酰基）酰胺（Li(G4)TFSI）的摩擦轨迹和回程环在负电位下比在正电位下呈现出更清晰的粘滑事件，表明在负电位下，一个锂离子层被吸附到 HOPG 晶格上，从而增强了粘滑事件。Li(G4)TFSI 的边界层摩擦数据表明，在 HOPG 上，所有电位下的摩擦力都很低。正电位下 TFSI 阴离子丰富的边界层比负电位下锂离子丰富的边界层更具润滑性。这些结果表明，所有电位下的边界层都是光滑的，能量主要通过粘滑事件耗散。相比之下，Li(G4)TFSI 在 Au(111)上的摩擦在正电位下显著高于负电位下，与同一电位下的 HOPG 相当。带负电荷的 HOPG 和 Au(111)表面的边界层摩擦相似，表明在负电位下，两种表面的边界层组成相似，富含锂离子。然而，在 Au(111)上，TFSI 丰富的边界层不如锂离子丰富的边界层润滑，这意味着阴离子重排而不是粘滑事件是主要的能量耗散途径。这一点通过 Au(111)上 Li(G4)NO 的边界摩擦得到证实，由于相同的阳离子丰富边界层组成，Li(G4)NO 在负电位下的摩擦与 Li(G4)TFSI 相似，但在正电位下的摩擦更高，这是由于 NO 丰富边界层中的能量耗散更高。
