Knot localization in adsorbing polymer rings.

We study by Monte Carlo simulations a model of a knotted polymer ring adsorbing onto an impenetrable, attractive wall. The polymer is described by a self-avoiding polygon on the cubic lattice. We find that the adsorption transition temperature, the crossover exponent phi, and the metric exponent nu are the same as in the model where the topology of the ring is unrestricted. By measuring the average length of the knotted portion of the ring, we are able to show that adsorbed knots are localized. This knot localization transition is triggered by the adsorption transition but is accompanied by a less sharp variation of the exponent related to the degree of localization. Indeed, for a whole interval below the adsorption transition, one can not exclude a continuous variation with temperature of this exponent. Deep into the adsorbed phase we are able to verify that knot localization is strong and well described in terms of the flat knot model.