PEG-based hydrogel membrane coatings

As a first step towards preparing fouling-resistant coatings for water purification membranes, three series of copolymer hydrogel networks were synthesized using poly(ethylene glycol) diacrylate (PEGDA) as the crosslinker and acrylic acid (AA), 2-hydroxyethyl acrylate (HEA), or poly(ethylene glycol) acrylate (PEGA) as comonomers. Copolymers containing varying amounts of PEGDA with each of these comonomers were prepared. Glass transition temperatures obeyed the Fox equation. Crosslink density strongly influenced water uptake and water permeability for materials of constant chemical composition. For example, the volume fraction of water sorbed by a 100 mol% PEGDA hydrogel was 0.61. However, introducing comonomers into the network reduced hydrogel crosslink density, and in hydrogels having the same ethylene oxide content, water sorption increased as crosslink density decreased. The highest water volume fraction observed was 0.72, obtained in a copolymer containing 80 mol% PEGA and 20 mol% PEGDA. Water permeability increased systematically with increasing water sorption, and water permeability coefficients ranged from 10 to 26 L μm/(m2 h bar). NaCl partition coefficients ranged from 0.36 to 0.53 (g NaCl/cm3 hydrogel)/(g NaCl/cm3 solution). NaCl diffusion coefficients varied little with polymer composition; in this regard, diffusion coefficient values ranged from 4.3 × 10−6 to 7.4 × 10−6 cm2/s. Based on contact angle measurements using n-decane in water, oil exhibited a low affinity for the surfaces of these polymers, suggesting that coatings prepared from such materials might improve the fouling resistance of membranes towards oily wastewater.