Thermally stable core-shell star-shaped block copolymers for antifouling enhancement of water purification membranes
Star-shaped block copolymers (SPs), consisting of a hydrophobic core and hydrophilic arms, are a new material architecture introduced to the area of antifouling coatings for water filtration membranes. The unique self-assembly behavior of these SPs on hydrophobic membranes surface allows the formation of an ultrathin coating (less than 15 nm), rendering a highly hydrophilic antifouling membrane surface. Here, we have judiciously examined several important structural and process parameters, such as the chemical composition of SPs and surface properties (e.g., surface potential, coverage, and wettability) driven by a mono- or bi-layered assembly of SPs, to acquire a highly hydrophilic and thermally stable antifouling coating on a hydrophobic ultrafiltration (polysulfone, PSF) membrane for oil sands produced water treatment. Among three types of SPs (e.g., SP1 with 100% amine, SP2 with 55% amine/45% PEG, and SP3 with 35% carboxylic acid/65% PEG moieties in the arms) and their variable coating conditions, the bilayer coating comprised of SP3 top-layer and SP1 bottom-layer exhibited the best hydrophilicity and anti-oil fouling efficiency showing 2–4 times higher water flux compared to an unmodified PSF membrane during the filtration of synthetic oil-water emulsions conducted in both constant flux mode and constant pressure mode. Outstanding antifouling efficiency of the bilayer coating toward natural organic matters (NOMs) was also verified by using bovine serum albumin (BSA) and humic acid (HA) as the model foulants. The bilayer-coated membrane retained more than 80% and 90% (for nano and micron size oil emulsion, respectively) of its initial antifouling efficiency even after rigorous thermal treatment for an extended period (80 °C for 1 week), which demonstrates its feasibility for high-temperature membrane operation.