Modeling adsorption processes on the core-shell-like polymer structures: star and comb topologies

TL;DR

This study uses Monte Carlo simulations to compare adsorption capacities of star and comb-like branched polymers, revealing that comb-like structures have higher capacity but lower strength, influenced by their architecture and branch separation.

Contribution

It introduces a lattice Monte Carlo model to analyze adsorption on core-shell branched polymers, highlighting differences between star and comb architectures.

Findings

Comb-like polymers have higher adsorption capacity than star-like polymers.

Adsorption strength is lower in comb-like structures compared to star-like ones.

Increasing branch separation enhances the differences in adsorption behavior.

Abstract

Coagulation-flocculation of pollutants and chelation of heavy metal ions are two widely used techniques in wastewater purification. Despite the differences between their respective mechanisms and inherent length scales, they bear much similarity on a larger scale, and can both be treated as adsorption of obstacles on a polymer structure. In this regime, their adsorbing efficiency is predominantly affected by conformation statistics of involved polymers, and this approach has been used in our previous studies based on lattice polymer model for a linear polymer adsorbent. There is a strong experimental evidence that branched adsorbents are more efficient than their linear counterparts. In this study we focus on two simplest representatives of the core-shell branched architectures: the star-like (with zero-dimensional point-like core) and comb-like polymers (with one-dimensional rigid core) with various number of branches, $f$, branch lengths, $N$, and branches separations, $S$ (for the case of comb-like structure). The polymers are grown on a lattice using the Monte Carlo simulations with the pruned-enriched Rosenbluth algorithm. The quantitative estimates for adsorption capacity in terms of adsorbed obstacles per monomer and the average number of bonds per adsorbed particle (average adsorption strength) have been evaluated in a wide range of parameters $f$, $N$, and $S$. Both the case of implicit diffusion of obstacles (with averaging over different arrangements of immobilized obstacles) and explicit diffusion of obstacles (allowing to study dynamics of adsorption process) have been analyzed. We found that comb-like polymers display the higher adsorption capacity but lower adsorption strength, comparing to the star-like polymers, and these effects are more pronounced with increasing branches separations $S$.