Surface-Tethered Zwitterionic Ultrathin Antifouling Coatings on Reverse Osmosis Membranes by Initiated Chemical Vapor Deposition

Poly[2-(dimethylamino)ethyl methacrylate-co-ethylene glycol dimethacry late] (PDE) thin films were synthesized via initiated chemical vapor deposition (iCVD) and reacted with 1,3-propane sultone to obtain the zwitterionic structure. The cross-linker ethylene glycol dimethacrylate (EGDMA) was utilized to make the copolymer insoluble in water. The composition of the copolymer was tuned by varying the flow rates of precursors and calculated from Fourier transform infrared spectroscopy (FTIR) spectra. The zwitterionic coatings were covalently grafted on to reverse osmosis (RO) membranes, and surface characterizations were carried out. Scanning electron microscope (SEM) and atomic force microscope (AFM) revealed that the iCVD zwitterionic coatings were conformal and smooth over the RO membrane, and the coating thickness can be measured by using ellipsometry. Salt rejection was not impaired by the coating. Permeation tests were carried out under different feed pressures, film thicknesses, and film compositions, showing a 15% to 43% reduction in permeation. Cell adhesion tests were carried out using Escherichia coli, and the coated RO membranes showed superior antifouling performance compared with the bare RO membrane. This is the first time that the library of iCVD functional groups has been extended to charged zwitterionic moieties, and the zwitterionic coatings have been applied on delicate substrates, such as RO membranes.