Swelling of Polyelectrolyte and Polyzwitterion Brushes by Humid Vapors

Swelling behavior of polyelectrolyte and polyzwitterion brushes derived from poly­(2-(dimethylamino)­ethyl methacrylate) (PDMAEMA) in water vapor is investigated using a combination of neutron and X-ray reflectivity and spectroscopic ellipsometry over a wide range of relative humidity (RH) levels. The extent of swelling depends strongly on the nature of the side-chain chemistry. For parent PDMAEMA, there is an apparent enrichment of water vapor at the polymer/air interface. Despite extensive swelling at high humidity level, no evidence of charge repulsion is found in weak or strong polyelectrolyte brushes. Polyzwitterionic brushes swell to a greater extent than the quaternized brushes studied. However, for RH levels beyond 70%, the polyzwitterionic brushes take up less water molecules, leading to a decline in water volume fraction from the maximum of ∼0.30 down to ∼0.10. Using a gradient in polymer chain grafting density (σ), we provide evidence that this behavior stems from the formation of inter- and intramolecular zwitterionic complexes

Reconstruction of Surfaces from Mixed Hydrocarbon and PEG Components in Water: Responsive Surfaces Aid Fouling Release

Coatings derived from surface active block copolymers (SABCs) having a combination of hydrophobic aliphatic (linear hydrocarbon or propylene oxide-derived groups) and hydrophilic poly­(ethlyene glycol) (PEG) side chains have been developed. The coatings demonstrate superior performance against protein adsorption as well as resistance to biofouling, providing an alternative to coatings containing fluorinated side chains as the hydrophobe, thus reducing the potential environmental impact. The surfaces were examined using dynamic water contact angle, captive air-bubble contact angle, atomic force microscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure analysis. The PS_8K-<i>b</i>-P­(E/B)_25K-<i>b</i>-PI_10K triblock copolymer precursor (K3) initially dominated the dry surface. In contrast to previous studies with mixed fluorinated/PEG surfaces, these new materials displayed significant surface changes after exposure to water that allowed fouling resistant behavior. PEG groups buried several nanometers below the surface in the dry state were able to occupy the coating surface after placement in water. The resulting surface exhibits a very low contact angle and good antifouling properties that are very different from those of K3. The surfaces are strongly resistant to protein adsorption using bovine serum albumin as a standard protein challenge. Biofouling assays with sporelings of the green alga <i>Ulva</i> and cells of the diatom <i>Navicula</i> showed the level of adhesion was significantly reduced relative to that of a PDMS standard and that of the triblock copolymer precursor of the SABCs