Dynamics of telechelic ionomers. Can polymers diffuse large distances without relaxing stress ?
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Abstract. -We consider dynamics of entangled telechelic ionomers in the limit of strong association, where there are no free chain ends. Stress relaxation occu s in such a system by an exchange between pairs of chain ends in the associated state. For complete relaxation of stress, an exchange went must take place on every entanglement strand. However, diffusion can occur on an arbitrarily shorter time scale, leading to the interesting result that chains can diffuse distances many times their coil size without relaxing stress. Due to the relation between stress and orientational correlations in polymers [I], there is a general belief that diffusion and stress relaxation are coiipled in polymer systems. There are examples where stress relaxation occurs much faster than diffusion, such as in a melt of star polymers [2], but the opposite case, where chains diffuse many times their sire without relaxing stress, is quite rare. One exception is semidilute solutions of disordered, rod-like polymers [I], for which translational diffusion is fast compared to rotational diffusion, which determines the time scale for stress relaxation. Due to the large aspect ratio of long rods, rotation through a small angle requires large translation. Another exception is a polydisperse system of flexible chains, where the measured diffusion coefficient reflects some average dominated by fast-moving (small) species, while the relaxation time is dictated by the slowest (largest) species. The question arises whether monodisperse flexible polymer chains can ever diffuse arbitrarily large distances without relaxing orientational correlations, and hence stress. The time scale for diffusion in polymers T is defined as the time it takes for a chain to diffuse a distance of order of its coil size, which we take to be its end-to-end distance R G hh’ " *, N being the number of monomers (Kuhn segments) and b being the monomer
