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We study the adhesion between differently processed glass and filled bromobutyl rubber in dry conditions, in water, and in silicone oil. The boundary line between contact and non-contact in adhesion experiments can be considered as a mode I crack, and we show that viscoelastic energy dissipation, close to the opening (or closing) crack tip and surface roughness, strongly affects the work of adhesion. We observe strong adhesion hysteresis and, in contrast to the Johnson–Kendall–Roberts theory prediction for elastic solids, this results in a pull-off force (and work of adhesion) which depends on the loading force and contact time. In particular, for the system immersed in water and silicone oil, we register very weak adhesive bonding. For glass ball with baked-on silicone oil, the pull-off force is nearly independent of the contact time, but this is not observed for the unprocessed glass surface. This is the authors’ accepted and refereed manuscript to the article. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in The Journal of Chemical Physics and may be found at https://aip.scitation.org/doi/10.1063/1.5025605.

We study the influence of surface roughness on the adhesion of elastic plates. Most real surfaces have roughness on many different length scales, and this fact is taken into account in our analysis. We consider in detail the case when the surface roughness can be described as a self-affine fractal, and study the plate-substrate pull-off force as a function of the surface roughness. Based on the theoretical results we discuss adhesion in biological systems, focusing on the adhesive pads of lizards. (C) 2003 American Institute of Physics.

The dynamics of expulsion of the last liquidlike monolayer of molecules confined between two surfaces (measured recently for the first time [J. Chem. Phys. 114, 1831 (2001)]) has been analyzed by solving the two-dimensional Navier-Stokes equation combined with kinetic Monte Carlo simulations. Instabilities in the boundary line of the expelled film produce a rough boundary for all length scales above a critical value. The squeeze-out of liquid is shown to result from the 2D-pressure gradient in the lubrication film in the contact area. The Monte Carlo simulations agrees well with experiments, reproducing most qualitative and quantitative features. In particular it shows the formation of small islands, which (in the absence of pinning mechanism) drift slowly to the periphery of the contact area. We calculate the drift velocity analytically as a function of the distance of the island to the periphery of the contact area. Experiments indicate that some kind of pinning mechanism prevails, trapping fluid pockets for very long times. When including such pinning areas in the simulations, three distinct squeeze phases and time scales were observed: (1) initial fast squeeze of most of the fluid; (2) slower squeeze of unpinned fluid pockets; (3) long term pinning of fluid pockets. We also show that a distribution of small pinning areas may produce a synergistic effect, slowing down the second phase of the squeeze, compared to a small number of big pinning areas. The paper presents a new stochastic numerical approach to problems of moving boundaries which naturally accounts for thermal fluctuations and their effect in unstable dynamics. (C) 2001 American Institute of Physics.

When rubber slides on a hard, rough substrate, the surface asperities of the substrate exert oscillating forces on the rubber surface leading to energy “dissipation” via the internal friction of the rubber. I present a discussion of how the resulting friction force depends on the nature of the substrate surface roughness and on the sliding velocity. I consider in detail the case when the substrate surface has a self affine fractal structure. I also present a theory for the area of real contact, both for stationary and sliding bodies, with elastic or elastoplastic properties. The theoretical results are in good agreement with experimental observation.

We calculate the electronic friction force acting on physisorbed molecules sliding on metal surfaces, where the metal is treated within the jellium model. We find that the contribution to the friction from the repulsive (Pauli repulsion) and attractive (van der Waals) adsorbate–substrate interactions are of similar magnitude. For small inert molecules and atoms such as C2H6 and Xe the calculated electronic friction (η∼108 s−1) is in good agreement with those deduced from surface resistivity and quartz crystal microbalance measurements. We discuss recent inelastic helium–atom scattering measurements for saturated hydrocarbons (hexane, octane and decane) on Cu(100) and show that the damping of the parallel adsorbate vibrations is dominated by the electronic friction while the phononic friction dominates for the perpendicular vibrations.

We generalize the Persson contact mechanics and rubber friction theory to the case where both surfaces have surface roughness. The solids can be rigid, elastic, or viscoelastic and can be homogeneous or layered. We calculate the contact area, the viscoelastic contribution to the friction force, and the average interface separation as a function of the sliding speed and the nominal contact pressure. We illustrate the theory with numerical results for the classical case of a rubber block sliding on a road surface. We find that with increasing sliding speed, the influence of the roughness on the rubber block decreases to the extent that only the roughness of the stiff counter face needs to be considered.

The exchange model of vibrational phase relaxation is studied. The vibrational line profile is obtained analytically in various limiting cases such as high temperature and large friction. Expressions for the first and second moments of the line profile are also presented.

We present a qualitative discussion of the nature and nonradiative decay of electronically excited states at metal surfaces. Within an Anderson–Newns type of Hamiltonian, we calculate, using the memory function formalism, the effect of the substrate on the energy and shape of the optical absorption or electron energy loss spectra and present illustrative numerical results. The theory is compared with experimental data for excited noble gas atoms on noble metal surfaces.