Design of Composite Polymer Brushes for Absorption of Contaminants from Water

Polymer brushes designed for environmental clean-up have emerged as a promising solution for addressing water contamination. Key design considerations include optimizing the brush density and thickness to maximize surface area and adsorption capacity, as well as the careful selection of functional groups and embedded absorbent materials tailored to target specific contaminants. The embedding of external adsorbent media (e.g., metal and metal oxide nanoparticles) within the brush is influenced by the configurations of both the brush and the particles, making the final structure prediction challenging. In this work, we employ coarse-grained molecular dynamics simulations with the MARTINI Force Field to explore the impact of grafting density and degree of polymerization on brush thickness and swelling dynamics, as well as the effects of ligands, particle size, and brush-particle interactions on diffusion within the brush. We systemize the conformational changes of dry polyethylene glycol (PEG) brushes and the resulting surface patterns, highlighting favorable chain lengths (within the range of 100-500 monomers) and grafting densities (up to 1 chain/nm²) required for desired surface coverage. Furthermore, by controlling nanoparticle diffusion into hydrated brushes through tuning size, ligand length and density, and mimicking different ligand chemistries by adjusting the strength of polymer-ligand interactions, we establish suitable configurations for each of the three interaction regimes: repulsion, surface rolling, and mixing. These findings lay the foundation for a novel class of adsorptive materials designed to capture harmful pollutants from aqueous environments, thereby contributing to environmental sustainability.