(317b) Fouling Resistant Temperature and Magnetic Field Responsive Nanofiltration Membranes

Nanofiltration membranes are finding increasing industrial applications.  Advantages over reverse osmosis membranes include much lower operating pressures yet significant rejection of multivalent ions.  However membrane fouling is a significant concern that frequently limits the commercial viability of nanofiltration membranes.  Here we have developed fouling resistant, self-cleaning nanofiltration membranes.  A method aimed at fouling mitigation and control, using stimuli-responsive polymer brushes attached to nanofiltration membranes is proposed and examined.

This study examines the effect of poly-N-isopropylacrylamide (PNIPAM) brushes attached to NF-270 membrane surface.  PNIPAM is a thermo-responsive polymer that has a lower critical solution temperature (LCST) of 32°C. Below the LCST PNIPAM brushes are in an expanded coil state and the intermolecular forces between the brushes and water are dominant - the polymer is hydrophilic. Above this temperature these grafted brushes form a collapsed dehydrated globular state as interactions between the brushes are more dominant.  By changing the temperature of the feed the grafted layer can switch between a more swollen (hydrophilic) and collapsed (hydrophobic) state leading to detachment of adsorbed foulants.

Changing the temperature of the bulk feed can be energy intensive.  We have developed a method to attach superparamagnetic nanoparticles to the ends of the grafted PNIPAM chains.  In an oscillating magnetic field heating of the superparamagnetic particles attached directly to the PNIPAM chains leads to collapse of the chains when the temperature is increased above the LCST of the grafted chains.  Thus we can change the conformation of the grafted chains without heating the bulk feed.  The effects of polymer grafting degree varying both the chain length and chain density are studied.  Our results indicate the importance of carefully tailoring the architecture of the grafted polymer chains in order to minimize membrane fouling.