Crowding and salinity effects on the structure of PEG-containing brushes

Strongly hydrated polymers are used as coatings for biofouling prevention, and poly(ethylene glycol) (PEG) is a widely used example of this. Wider use of PEG is limited by insufficient stability but this can be improved by adding PEG sidechains to a more stable polymer backbone. However, this alters the structural properties in ways that can be difficult to predict. Here, we will explore the properties of polymer brushes with PEG sidechains from two aspects: i) These brushes show thickness-dependent antifouling performance, which has been associated to differences in hydration and crowding of the polymer with thickness, but further details about the structure, in particular qualitative and quantitative differences in the chain segment density distributions, would considerably improve our understanding and facilitate the development of these brushes into practical coatings. ii) Poor antifouling performance of PEG in solutions of high salinity is hypothesized to be an effect of the recently proposed charging of PEG in aqueous solutions due to adsorption of hydronium ions. If correct, this would imply some degree of polyelectrolyte properties, and subsequent structural changes at high salinity, which we will explore as well.