Friction mechanisms at polymer–solid interfaces (original) (raw)
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Sliding Friction at a Rubber/Brush Interface
Langmuir, 2004
We study the friction of a poly(dimethylsiloxane) (PDMS) rubber network sliding, at low velocity, on a substrate on which PDMS chains are end-tethered. We thus clearly evidence the contribution to friction of the pull-out mechanism of chain-ends that penetrate into the network. This interfacial dissipative process is systematically investigated by probing the velocity dependence of the friction stress and its variations with the grafting density and molecular weight of the tethered chains. This allows us to confirm semi-quantitatively the picture of arm retraction relaxation of the grafted chains proposed in models of slippage at a network/brush interface.
Europhysics Letters (EPL), 2005
We study the friction between a flat solid surface where polymer chains have been end-grafted and a cross-linked elastomer at low sliding velocity. The contribution of isolated grafted chains' penetration in the sliding elastomer has been early identified as a weakly velocity dependent pull-out force. Recent experiments have shown that the interactions between the grafted chains at high grafting density modify the friction force by grafted chain. We develop here a simple model that takes into account those interactions and gives a limit grafting density σ l beyond which the friction no longer increases with the grafting density, in good agreement with the experimental data.
Incidence of the molecular organization on friction at soft polymer interfaces
Soft Matter, 2011
Polymer molecules strongly anchored to a solid substrate and interdigitated into bulk crosslinked elastomer have been shown recently to efficiently promote adhesion and friction between substrate and elastomer. Concerning friction, the regime of low surface coverage in surface anchored chains has been fully and quantitatively accounted for by the pull off mechanisms, where individual chains are dynamically extracted from the elastomer. Then, the stretching energy of these chains dominates the friction losses. We focus here on the dense surface coverage regime. We present systematic experiments performed on the polydimethylsiloxane (PDMS) -silica system, and determine molecular weight and sliding velocity dependences of the friction stress. We show that the friction is dominated by the shear thinning of the grafted layer confined between the elastomer and the substrate, and responding to the shear solicitation like a melt, but with very long relaxation times. We also show that the friction stress appears highly sensitive to the molecular organization inside the surface anchored polymer layer, comparing end grafted and strongly adsorbed layers having otherwise the same molecular characteristics (molecular weight of the chains, and thickness of the surface anchored layer).
Solid-like friction of a polymer chain
The European Physical Journal E, 2000
We propose a simple friction model for isolated polymer chains on a solid substrate. The chains are pulled at constant velocity by one end, the other end can be trapped on the solid substrate on localised sites. We focus on the energy dissipation due to the traps. This simple model leads to non trivial friction laws, depending on the velocity and the distance between traps. Some refinements of the model such as the effect of thermal fluctuations are also reported.
We present a model for the steady dynamic friction of a block of an elastomer, sliding steadily on a hard surface. The model uses population balance of the bonds between the hard surface and the polymer chains of the elastomer to estimate the force of friction. Although the basic premises of the present model are the same as those of the Schallamach model for dynamic friction (1963), the present formulation is a clearer representation of the phenomena involved. Moreover, the model is not based on the ergodic hypothesis and is therefore more versatile. It also allows us to correct the error in the expression for the force of friction in the Schallamach model. The present model exhibits the same qualitative trends as the Schallamach model. However, there are significant quantitative differences between the two models. We also show that our expression for the force of friction is equivalent to that obtained by the Chernyak and Leonov (1986) model, which is based on the ergodic hypothesis. The model is further modified to account for both the non-Hookean extension of the bonded chains and the viscous retardation effect. The model is validated using the experimental data of Vorvolakos and Chaudhury (2003) on sliding of crosslinked PDMS solid on silane coated silicon wafer. From this analysis, scaling laws, which relate the model parameters to the molecular weight of the polymer chains and the temperature, are derived and justified.
A molecular theory of adhesive rubber friction
Journal of Physics A: Mathematical and General, 1975
A theory of adhesive rubber friction is proposed where the final expression for the coefficient of friction obeys the Williams-Landel-Ferry transform and correlates with the viscoelastic shear loss modulus, as shown by Grosch and others. Our approach is based on the beadspring model for polymer chains of Rouse.
Interfacial friction between semiflexible polymers and crystalline surfaces
The Journal of Chemical Physics, 2012
The results obtained from molecular dynamics simulations of the friction at an interface between polymer melts and weakly attractive crystalline surfaces are reported. We consider a coarse-grained bead-spring model of linear chains with adjustable intrinsic stiffness. The structure and relaxation dynamics of polymer chains near interfaces are quantified by the radius of gyration and decay of the time autocorrelation function of the first normal mode. We found that the friction coefficient at small slip velocities exhibits a distinct maximum which appears due to shear-induced alignment of semiflexible chain segments in contact with solid walls. At large slip velocities the decay of the friction coefficient is independent of the chain stiffness. The data for the friction coefficient and shear viscosity are used to elucidate main trends in the nonlinear shear rate dependence of the slip length. The influence of chain stiffness on the relationship between the friction coefficient and the structure factor in the first fluid layer is discussed.
Polymer-polymer friction: Adhesion dependence
Journal of Synthetic Lubrication, 1995
The friction of pure polyethylene and acrylate grafed films or mixtures of polyethylene and a polyiethylene-butylacrylate-maleic anhydride) terpolymer is examined at low speed for sliding on a poly(methylmethacry1ate) (PMMA) or polyvinylchloride (PVC) substrate. In all cases, the friction coefficient p at equilibrium is proportional to the adhesion energy of the same films as determined by a peel test. This study shows how much for smooth surjimes, interjiacial and mechanical properties intervene simultaneously in polymer-polymer friction.