Friction in strongly confined polymer melts: Effect of polymer bridges

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Abstract
We propose a molecular theory of friction in confined polymer melts between atomically smooth surfaces, taking polymer bridges between the surfaces into account. Using the activation friction model, we consider the bridge adsorption-desorption dynamics and calculate the macroscopic friction force (the tangential stress) in the system as a function of the imposed velocity. We show that the bridges result in the regime where the friction force decreases with the increase of the imposed velocity. The friction force passes through maximum and minimum values in the crossover range between linear and nonlinear regimes. We also investigate the stability of sliding in the regime with decreasing friction force.