Adsorption of random copolymers on disordered surfaces

Monte Carlo simulations are used to study adsorption of random heteropolymers on disordered substrates. The adsorbent surface is modelled as an impenetrable wall with the random distribution of sites characterised by short-ranged segment-specific interactions with the polymer. Spatial fluctuations in the interaction strength are described as a Gaussian process with zero mean and variance al which is proportional to the site/segment potential, and to the loading of sites on the surface. In all cases, a moderate depletion in the polymer density is observed at small surface loading. Upon increasing al, the polymer begins to adsorb on the surface. At a certain threshold loading, we observe a sharp second adsorption transition followed by gradual saturation. The transition is interpreted in terms of pattern matching; i.e. the heteropolymers accomodate themselves at surface domains with site distributions that match the configuration and the sequence of the chain when the sequence and surface site distributions are related in a special way. Distinct peaks in heat capacity and compressibility observed at the adsorption transition point to a first order process envisaged in earlier replica/mean-field analysis. These results suggest that random heteropolymers with designed sequence statistics can 'recognise' multifunctional disordered surfaces due to statistical pattern-matching. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.