ABSTRACT
Chain molecules resist deformation or confinement, owing to elasticity and excluded volume. Chain conformations can be perturbed by the presence of a surface. For polymers that are tethered to an impenetrable surface, the free ends tend not to be at the surface but terminate at a distance proportional to away from the surface. Confining a chain molecule to small spaces leads to a reduction in the number of available conformations. So there is a free energy that opposes the entrance of polymer chains into confined spaces. After stretching in shear flow, polymers retract, causing elasticity in solutions, called viscoelasticity. The Rouse–Zimm theory explains the dependence of the relaxation time on the polymer molecular weight in dilute solutions. For longer chains at higher concentrations, or in gels, the relaxation and diffusional motions have been modeled in terms of snakelike reptation processes.
