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Understanding the Dynamics of Unentangled Associating Polymers by Means of Molecular Simulations

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Associating polymers are a family of macromolecules that have sticky groups that can create intermolecular reversible bonds with energies on the order of a few tens of kT. These bonds can associate and dissociate easily at room temperature and, above the percolation threshold, associating polymers form transient solid soft materials. These materials have many applications as sacrificial components in tough physical double networks, synthetic matrices for tissue engineering, injectable biomaterials for minimally invasive surgery or self-healing soft materials. In all cases, it is very important to understand and predict both the dynamical response of the material (i.e. its mechanical properties or the diffusion of the network forming constituents). Recent experiments have revealed that a variety of unentangled associative polymers with different architectures and different nature of the associating interactions exhibit an unexpected diffusion behavior, with a phenomenological superdiffusive scaling at length-scales and time-scales much longer than the molecular size and relaxation time. In this talk, I will discuss a new coarse-grained molecular model of unentangled associating polymers that successfully explains the observed anomalous behavior and reveals three basic mechanisms of molecular diffusion: caging dynamics, walking diffusion and molecular hopping, all of which depend very strongly on polymer concentration, length of the segments between stickers and the association/dissociation kinetics. The apparent superdiffusive scaling results primarily from molecular hopping, which dominates the dynamics at long times if the kinetics of attachment are much slower than the relaxation time of polymer strands between stickers and the formation of loops is favourable. Finally, I will discuss how the molecular parameters affect the diffusivity and relaxation modulus, as well as the non-linear flow behaviour, and how to confirm other predictions of the model experimentally and by means of Molecular Dynamics simulations.

This talk is part of the Theory - Chemistry Research Interest Group series.

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