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Author: Müser, Martin H. × DDC: 530 × WGL Institute: INM ×

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Now showing 1 - 4 of 4
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    Force microscopy of layering and friction in an ionic liquid
    (Bristol : IOP Publishing, 2014) Hoth, Judith; Hausen, Florian; Müser, Martin H.; Bennewitz, Roland
    The mechanical properties of the ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py1,4][FAP]) in confinement between a SiOx and a Au(1 1 1) surface are investigated by means of atomic force microscopy (AFM) under electrochemical control. Up to 12 layers of ion pairs can be detected through force measurements while approaching the tip of the AFM to the surface. The particular shape of the force versus distance curve is explained by a model for the interaction between tip, gold surface and ionic liquid, which assumes an exponentially decaying oscillatory force originating from bulk liquid density correlations. Jumps in the tip–sample distance upon approach correspond to jumps of the compliant force sensor between branches of the oscillatory force curve. Frictional force between the laterally moving tip and the surface is detected only after partial penetration of the last double layer between tip and surface.
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    On the viscous dissipation caused by randomly rough indenters in smooth sliding motion
    (Amsterdam : Elsevier, 2021) Sukhomlinov, Sergey; Müser, Martin H.
    The viscous dissipation between rigid, randomly rough indenters and linearly elastic counter bodies sliding past them is investigated using Green’s function molecular dynamics. The study encompasses a variety of models differing in the height spectra properties of the rigid indenter, in the viscoelasticity of the elastomer, and in their interaction. All systems reveal the expected damping linear in sliding velocity at small and a pronounced maximum at intermediate . Persson’s theory of rubber friction, which is adopted to the studied model systems, reflects all observed trends. However, close quantitative agreement is only found up to intermediate sliding velocities. Relative errors in the friction force become significant once the contact area is substantially reduced by sliding.
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    Significance of Elastic Coupling for Stresses and Leakage in Frictional Contacts
    ([Ithaca, NY] : Arxiv.org, 2023) Müller, Christian; Müser, Martin H.; Carbone, Giuseppe; Menga, Nicola
    We study how the commonly neglected coupling of normal and in-plane elastic response affects tribological properties when Hertzian or randomly rough indenters slide past an elastic body. Compressibility-induced coupling is found to substantially increase maximum tensile stresses, which cause materials to fail, and to decrease friction such that Amontons law is violated macroscopically even when it holds microscopically. Confinement-induced coupling increases friction and enlarges domains of high tension. Moreover, both types of coupling affect the gap topography and thereby leakage. Thus, coupling can be much more than a minor perturbation of a mechanical contact.
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    Analytical and numerical results for the elasticity and adhesion of elastic films with arbitrary Poisson’s ratio and confinement
    (London [u.a.] : Taylor & Francis, 2022) Müller, Christian; Müser, Martin H.
    We present an approximate, analytical treatment for the linearly elastic response of a film with arbitrary Poisson's ratio (Formula presented.), which is indented by a flat cylindrical punch while resting on a rigid foundation. Our approach is based on a simple scaling argument allowing the vast changes of the elastomer’s effective modulus (Formula presented.) with the ratio of film height (Formula presented.) and indenter radius (Formula presented.) to be described with a compact, analytical expression. This yields exact asymptotics for large and small reduced film heights (Formula presented.), whereby it also reproduces the observation that (Formula presented.) has a pronounced minimum for (Formula presented.) at (Formula presented.). Using Green’s function molecular dynamics (GFMD), we demonstrate that the predictions for (Formula presented.) are reasonably correct and generate accurate reference data for effective modulus and pull-off force. GFMD also reveals that the nature of surface instabilities occurring during stable crack growth as well as the crack initiation itself depend sensitively on the way how continuum mechanics is terminated at small scales, that is, on parameters beyond the two dimensionless numbers (Formula presented.) and (Formula presented.) defining the continuum problem.