Zhang Yunxiao, Li Hua, Wang Jianan, Silvester Debbie S, Warr Gregory G, Atkin Rob
School of Molecular Sciences, The University of Western Australia, Perth, Western Australia, Australia.
School of Molecular Sciences, The University of Western Australia, Perth, Western Australia, Australia; Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth, Western Australia, Australia.
J Colloid Interface Sci. 2025 Jan 15;678(Pt A):355-364. doi: 10.1016/j.jcis.2024.08.187. Epub 2024 Aug 25.
The friction and interfacial nanostructure of a water-in-surface-active ionic liquid mixture, 1.6 M 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate ([BMIm][AOT]), can be tuned by applying potential on Au(111) and stainless steel.
Atomic force microscopy (AFM) was used to examine the friction and interfacial nanostructure of 1.6 M [BMIm][AOT] on Au(111) and stainless steel at different potentials.
Superlubricity (vanishing friction) is observed for both surfaces at OCP+1.0 V up to a surface-dependent critical normal force due to [AOT] bilayers adsorbing strongly to the positively charged surface thus allowing AFM tip to slide over solution-facing hydrated anion charged groups. High-resolution AFM imaging reveals ripple-like features within near-surface layers, with the smallest amplitudes at OCP+1 V, indicating the highest structural stability and resistance to thermal fluctuations due to highly ordered boundary [AOT] bilayers templating robust near-surface layers. Exceeding the critical normal force at OCP+1.0 V causes the AFM tip to penetrate the hydrated [AOT] layer and slide over alkyl chains, increasing friction. At OCP and OCP-1.0 V, higher friction correlates with more pronounced ripples, attributed to the rougher templating [BMIm] boundary layer. Kinetic experiments show that switching from OCP-1.0 V to OCP+1.0 V achieves superlubricity within 15 s, enabling real-time friction control.
通过在金（111）和不锈钢上施加电势，可以调节表面活性离子液体混合物1.6M 1-丁基-3-甲基咪唑鎓1,4-双-2-乙基己基磺基琥珀酸盐（[BMIm][AOT]）的摩擦力和界面纳米结构。
使用原子力显微镜（AFM）在不同电势下检测1.6M [BMIm][AOT]在金（111）和不锈钢上的摩擦力和界面纳米结构。
在开路电位（OCP）+1.0V时，两个表面均观察到超润滑性（摩擦力消失），直至达到与表面相关的临界法向力，这是由于[AOT]双层强烈吸附到带正电的表面，从而使AFM探针能够在面向溶液的水合阴离子带电基团上滑动。高分辨率AFM成像揭示了近表面层内的波纹状特征，在OCP +1V时振幅最小，这表明由于高度有序的边界[AOT]双层模板化了坚固的近表面层，其具有最高的结构稳定性和对热波动的抵抗力。在OCP +1.0V时超过临界法向力会导致AFM探针穿透水合[AOT]层并在烷基链上滑动，从而增加摩擦力。在OCP和OCP -1.0V时，较高的摩擦力与更明显的波纹相关，这归因于更粗糙的模板化[BMIm]边界层。动力学实验表明，从OCP -1.0V切换到OCP +1.0V可在15秒内实现超润滑，从而实现实时摩擦控制。
