Transitions of tethered polymer chains: A simulation study with the bond fluctuation lattice model

TL;DR

This study uses Monte Carlo simulations with advanced sampling techniques to explore the phase transitions of tethered polymer chains under various solvent and surface conditions, revealing detailed behaviors of adsorption and collapse phenomena.

Contribution

It introduces a comprehensive simulation approach combining Wang-Landau and umbrella sampling for the bond-fluctuation model, providing new insights into polymer phase behavior.

Findings

Good agreement with Metropolis Monte Carlo for adsorption.

Collapse transition shows a two-step process on attractive surfaces.

Similar behavior observed between tethered and free chains during collapse.

Abstract

A polymer chain tethered to a surface may be compact or extended, adsorbed or desorbed, depending on interactions with the surface and the surrounding solvent. This leads to a rich phase diagram with a variety of transitions. To investigate these transitions we have performed Monte Carlo simulations of a bond-fluctuation model with Wang-Landau and umbrella sampling algorithms in a two-dimensional state space. The simulations' density of states results have been evaluated for interaction parameters spanning the range from good to poor solvent conditions and from repulsive to strongly attractive surfaces. In this work, we describe the simulation method and present results for the overall phase behavior and for some of the transitions. For adsorption in good solvent, we compare with Metropolis Monte Carlo data for the same model and find good agreement between the results. For the collapse transition, which occurs when the solvent quality changes from good to poor, we consider two situations corresponding to three-dimensional (hard surface) and two-dimensional (very attractive surface) chain conformations, respectively. For the hard surface, we compare tethered chains with free chains and find very similar behavior for both types of chains. For the very attractive surface, we find the two-dimensional chain collapse to be a two-step transition with the same sequence of transitions that is observed for three-dimensional chains: a coil-globule transition that changes the overall chain size is followed by a local rearrangement of chain segments.