Self-consistent field theory for the distal ordering of adsorbed polymer: comparison with the Scheutjens-Fleer model

TL;DR

This paper compares a self-consistent field theory for adsorbed polymers with the Scheutjens-Fleer model, showing good agreement for various solvent conditions and extending the theory to account for non-local interactions.

Contribution

It provides a detailed comparison between a weak adsorption model and the Scheutjens-Fleer model, extending the former to include non-local interactions for better accuracy.

Findings

Quantitative agreement in segment density profiles for good solvents.

Extension of the model to theta and poor solvents.

Accurate description of transition from oscillatory to monotonic decay.

Abstract

In a previous article [E.M. Blokhuis, K.I. Skau, and J.B. Avalos, J. Chem. Phys. 119, 3483 (2003)], a self-consistent field formalism was derived for weakly adsorbing polymers, valid for any chain length. It was shown that the presence of a solid wall induces an ordering of the polymers on the scale of the radius of gyration far away from the surface (the distal region). These oscillations in the polymer concentration profile were first noted in work by Semenov et al., and later observed in numerical solutions of the Scheutjens and Fleer self-consistent field model. In the present paper, we compare the weak adsorption model in more detail with the numerical results from the Scheutjens and Fleer model. Quantitative agreement is obtained for the polymer segment density profile in a good (athermal) solvent. For theta solvent and poor solvent conditions, it is necessary to extend the weak adsorption model to take the non-local character of the polymer-solvent interaction into account. Again, quantitative agreement is obtained for the polymer segment density profile, in particular for the transition from an oscillatory decaying profile to a monotonically decaying profile when the bulk polymer density is below a certain threshold value.