Microslips to "Avalanches" in Confined, Molecular Layers of Ionic Liquids.
We have measured forces between mica surfaces across two hydrophobic ionic liquids with a surface forces apparatus. Both surface-adsorbed water and alkyl-chain length on the imidazolium cation influence the structure of the nanoconfined film and the dynamics of film-thickness transitions. Friction shows accumulative microslips as precursors to collective "avalanches" that abruptly reduce friction momentarily. This behavior is interpreted as a consequence of interlayer ion correlations within the 1 to 2 nm thick film; we identify this to be analogous to the friction response of crackling noise systems over a broad range of sizes.
†Lab. for Surface Science and Technology, Dept. of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.
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Espinosa-Marzal
†Lab. for Surface Science and Technology, Dept. of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.
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Arcifa
†Lab. for Surface Science and Technology, Dept. of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.|‡Dipartimento di Scienze Chimiche e Geologiche, Università di Cagliari, S.S. 554 Bivio per Sestu, 09042 Cagliari, Italy.
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Rossi
†Lab. for Surface Science and Technology, Dept. of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.
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Spencer
crackling noise systems; friction; ionic liquids; nanoconfined liquids; stick−slip; surface forces apparatus; water