Electrostatic Fields Stimulate Absorption of Small Neutral Molecules in Gradient Polyelectrolyte Brushes

Molecules can partition from a solution into a polymer coating, leading to a local enrichment. If one can control this enrichment via external stimuli, one can implement such coatings in novel separation technologies. Unfortunately, these coatings are often resource intensive as they require stimuli in the form changes of bulk solvent conditions such as acidity, temperature, or ionic strength. Electrically driven separation technology may provide an appealing alternative, as this will allow local, surface-bound stimuli instead of system-wide bulk stimuli to induce responsiveness. Therefore, we investigate via coarse grained molecular dynamics simulations the possibility of using coatings with charged moieties, specifically gradient polyelectrolyte brushes, to control the enrichment of the neutral target molecules near the surface with applied electric fields. We find that targets which interact more strongly with the brush show both more absorption and a larger modulation by electric fields. For the strongest interactions evaluated in this work, we obtained absorption changes of over 300 % between the collapsed and extended state of the coating.