Adsorption of symmetric random copolymer onto symmetric random surface: the annealed case

TL;DR

This study models the adsorption behavior of symmetric random copolymers on symmetric random surfaces using an annealed approximation, revealing that composition remains constant while rearrangements enhance adsorption, with symmetry violations causing component interconversion.

Contribution

It introduces a two-dimensional partially directed walk model to analyze symmetric copolymer-surface adsorption in the annealed case, highlighting composition stability and rearrangement effects.

Findings

A posteriori compositions match a priori probabilities and remain unchanged with temperature.

Rearrangements of monomers and sites improve matching and adsorption.

Symmetry violations lead to component interconversion and altered adsorption behavior.

Abstract

Adsorption of a symmetric (AB) random copolymer (RC) onto a symmetric (ab) random heterogeneous surface (RS) is studied in the annealed approximation by using a two-dimensional partially directed walk model of the polymer. We show that in the symmetric case, the expected a posteriori compositions of the RC and the RS have correct values (corresponding to their a priori probabilities) and do not change with the temperature, whereas second moments of monomers and sites distributions in the RC and RS change. This indicates that monomers and sites do not interconvert but only rearrange in order to provide better matching between them and, as a result, a stronger adsorption of the RC on the RS. However, any violation of the system symmetry shifts equilibrium towards the major component and/or more favorable contacts and leads to interconversion of monomers and sites.