Non-entropic theory of rubber elasticity: Flexible chains grafted on a rigid surface

The elastic response is studied of (i) a single flexible chain grafted on a rigid plane and (ii) an ensemble of non-interacting tethered chains. It is demonstrated that the entropic theory of rubber elasticity may lead to conclusions that disagree with experimental data. A modification of the conventional approach is proposed, where the end-to-end distribution function (treated as the governing variable) is replaced by the average energy of a chain. It is revealed that this refinement ensures an adequate description of the mechanical behavior of flexible chains. Results of numerical simulation are compared with observations on uniaxial compression of a layer of grafted chains, and an acceptable agreement is shown between predictions of the model and the experimental data. Based on the analysis of combined compression and shear, a novel micro-mechanism is proposed for the reduction of friction of polymer melts at rigid walls.