The localized phase of disordered copolymers with adsorption

G. Giacomin, F. L. Toninelli

Published 2005-10-03, updated 2006-03-29Version 2

We analyze the localized phase of a general model of a directed polymer in the proximity of an interface that separates two solvents. Each monomer unit carries a charge, $\omega_n$, that determines the type (attractive or repulsive) and the strength of its interaction with the solvents. In addition, there is a polymer--interface interaction and we want to model the case in which there are impurities $\tilde\omega_n$, that we call again charges, at the interface. The charges are distributed in an in--homogeneous fashion along the chain and at the interface: more precisely the model we consider is of quenched disordered type. It is well known that such a model undergoes a localization/delocalization transition. We focus on the localized phase, where the polymer sticks to the interface. Our new results include estimates on the exponential decay of averaged correlations and the proof that the free energy is infinitely differentiable away from the transition. Other results we prove, instead, generalize earlier works that typically deal either with the case of copolymers near an homogeneous interface ($\tilde\omega\equiv 0$) or with the case of disordered pinning, where the only polymer--environment interaction is at the interface ($\omega\equiv 0$). Moreover, with respect to most of the previous literature, we work with rather general distributions of charges (we will assume only a suitable concentration inequality).