A New Strategy for Ultralow Biofouling Membranes : Uniform and Ultrathin Hydrophilic Coatings Using Liquid Carbon Dioxide

Abstract

Highly stable, uniform and ultrathin hydrophilic polymer coatings on the surface as well as in the pores of a PVDF microfiltration (MF) membrane are obtained by coating a hydrophilic monomer in liquid carbon dioxide (l-CO2) followed by subsequent crosslinking reaction. Polyethylene glycol diacrylate (PEGDA, Mn ~258 g/mol) is used as the l-CO2 soluble hydrophilic monomer source and azobisisobutyronitrile (AIBN) was used as a radical initiator. The extremely low surface tension and the low viscosity of l-CO2 result in ultrathin and uniform PEG coatings on the hydrophobic polyvinylidene fluoride (PVDF) microfiltration membrane. The chemical composition, morphology, and the depth profiles of the PEGcoated membranes are characterized in detail using X-ray photoelectron spectroscopy, scanning electron microscopy, electron probe microanalysis and energy dispersive X-ray microanalysis. Long-term permeation flux test using a bovine serum albumin solution shows that the 1.0 wt% PEGDA-coated membrane using l-CO2 exhibits 1.34 times larger BSA solution flux than that of the uncoated PVDF membrane, and 1.3 times larger flux than that of a commercial hydrophilic membrane. Fouling resistance estimation shows that the 1 wt% PEGDA-coated membrane exhibits ~30% lower internal fouling resistance than the pristine membrane, and ~24% lower internal fouling resistance than the commercial hydrophilic membrane.