Macroinitiator-mediated photoreactive coating of membrane surfaces with antifouling hydrogel layers

Applying a hydrophilic layer to the membrane surface is one common strategy to control membrane fouling. This work focuses on hydrophilic membrane coating materials synthesized from poly(ethylene glycol) (PEG)-based hydrogels and application of thin hydrogel layers from such polymers on the surface of composite polyamide nanofiltration membranes. The approach of using macroinitiator-mediated synthesis cum anchoring of a hydrogel layer on the membrane was explored to reduce or avoid homopolymerization in bulk solution and prevent delamination of the antifouling layer from membrane surface. Cationic macroinitiators were based on poly(2-dimethylamino-ethyl methacrylate-co-2-hydroxyethyl methacrylate) obtained by radical copolymerization and comprised photoinitiator side groups linked to the poly(2-hydroxyethyl methacrylate) segments. Adsorption of the macroinitiator to the membrane surface and preparation of hydrogel coatings on polyamide composite membranes via photo-initiated in situ graft and cross-linking copolymerization were studied in detail. The modification degree and its effect on the membrane properties was characterized with respect to membrane chemistry by ATR-IR spectroscopy, surface charge by zeta potential, surface wettability by contact angle, and with respect to pure water permeability and salt rejection. The propensity to protein fouling was also investigated. The results indicate that hydrogel modified membranes have an improved fouling resistance compared to pristine membranes, and that this approach has the potential to become a generic approach for a controlled surface functionalization using a simple two-step protocol.