pH-Tolerant Wet Adhesion of Catechol Analogs.

The need for improved wet adhesives has driven research on mussel-inspired materials incorporating dihydroxyphenylalanine (DOPA) and related analogs of the parent catechol, but their susceptibility to oxidation limits practical application of these functionalities. Here, we investigate the molecular-level adhesion of the catechol analogs dihydroxybenzamide (DHB) and hydroxypyridinone (HOPO) as a function of pH. We find that the molecular structure of the catechol analogs influences their susceptibility to oxidation in alkaline conditions, with HOPO emerging as a particularly promising candidate for pH-tolerant adhesives for diverse environmental conditions.

Ionic strength dependent forces between end-grafted Poly(sulfobetaine) films and mica.

The molecular surface properties of zwitterionic polymer coatings are central to their ultra-low fouling properties and effectiveness as steric stabilizers in concentrated salt solutions. Here, Surface Force Apparatus measurements quantified the molecular forces between end-grafted poly(sulfobetaine) methacrylate thin films and mica, as a function of the chain grafting density and ionic strength. These results demonstrate that, at the ionic strengths considered, end-grafted poly(sulfobetaine) films can be described by models for polymers in good solvent. Parameters determined from data fits to the Milner-Witten-Cates or Dolan and Edwards models for dense or dilute chains, respectively, varied with ionic strength, in ways that reflect poly(sulfobetaine) swelling and the increased excluded volume strength of chain segments. These force measurements provide new insight into how polymer coverage and salt cooperate to regulate repulsive poly(sulfobetaine) steric barriers. These findings have implications for the design of grafted poly(sulfobetaine) as colloidal stabilizers or nonfouling surface coatings.

Forces between mica and end-grafted statistical copolymers of sulfobetaine and oligoethylene glycol in aqueous electrolyte solutions.

This study quantified the interfacial forces associated with end-grafted, statistical (AB) co-polymers of sulfobetaine methacrylate (SBMA) and oligoethylene glycol methacrylate (OEGMA) (poly(SBMA-co-OEGMA)). Surface force apparatus measurements compared forces between mica and end-grafted copolymers containing 0, 40, or 80 mol% SBMA. Studies compared forces measured at low grafting density (weakly overlapping chains) and at high density (brushes). At high density, the range of repulsive forces did not change significantly with increasing SBMA content. By contrast, at low density, both the range and the amplitude of the repulsion increased with the percentage of SBMA in the chains. The ionic strength dependence of the film thickness and repulsive forces increased similarly with SBMA content, reflecting the increasing influence of charged monomers and their interactions with ions in solution. The forces could be described by models of simple polymers in good solvent. However, the forces and fitted model parameters change continuously with the SBMA content. The latter behavior suggests that ethyene glycol and sulfobetaine behave as non-interacting, miscible monomers that contribute independently to the interfacial forces. The results suggest that molecular scale properties of statistical poly (SBMA-co-OEGMA) films can be readily tuned by simple variation of the monomer ratios.