Polymer desorption under pulling: a novel dichotomic phase transition

TL;DR

This paper presents a theoretical and simulation study of a self-avoiding polymer on an adhesive substrate under pulling, revealing a first-order dichotomic phase transition with new insights into the critical adsorption exponent.

Contribution

It introduces an analytical GCE approach to describe polymer detachment and clarifies the nature of the phase transition and the critical exponent dependence on loop interactions.

Findings

Detachment transition is first order and dichotomic.

Critical adsorption exponent depends on loop interactions.

Theoretical predictions are confirmed by Monte Carlo simulations.

Abstract

We show that the structural properties and phase behavior of a self-avoiding polymer chain on adhesive substrate, subject to pulling at the chain end, can be obtained by means of a Grand Canonical Ensemble (GCE) approach. We derive analytical expressions for the mean length of the basic structural units of adsorbed polymer, such as loops and tails, in terms of the adhesive potential and detachment force, and determine values of the universal exponents which govern their probability distributions. Most notably, the hitherto controversial value of the critical adsorption exponent $\phi$ is found to depend essentially on the interaction between different loops. The chain detachment transition turns out to be of the first order, albeit dichotomic, i.e., no coexistence of different phase states exists. These novel theoretical predictions and the suggested phase diagram of the adsorption-desorption transformation under external pulling force are verified by means of extensive Monte Carlo simulations.