(386c) Remote Performance Modulation of Ultrafiltration Membranes By Magnetically and Thermally Responsive Polymer Chains

Stimuli responsive ultrafiltration membranes that respond to both an external magnetic field and the local temperature have been developed. Surface initiated activator generated electron transfer (AGET) atom transfer radical polymerization (ATRP) has been used to graft poly(N-isopropylacrylamide) (PNIPAm) from the surface of 300 kDa regenerated cellulose ultrafiltration membranes. A superparamagnetic nanoparticle was attached to the end of the polymer chain. The polymerization initiator was selectively attached to the entire membrane surface, only the outer membrane surface or only the inner pore surface. The DI water flux as well as the flux and rejection of bovine serum albumin (BSA) was investigated in the absence and presence of a 20 and 1000 Hz oscillating magnetic field.

In an oscillating magnetic field, the tethered superparamagnetic nanoparticles can cause movement of the grafted PNIPAm chains or induce heating. A 20 Hz oscillating magnetic field maximizes movement of the grafted PNIPAm chains. For PNIPAM chains grafted from the outer membrane surface movement of the grafted polymer chains leads to break up of the concentration polarization boundary layer. This results in an increase in the observed rejection of partially rejected BSA. A 1000 Hz oscillating magnetic field leads to greater induced heating. PNIPAm displays a lower critical solution temperature (LCST) at 32 °C. Since the heat is generated at the interface with the PNIPAm chains heating leads to dehydration and collapse of the PNIPAm chains above their LCST. For PNIPAm grafted from the inner pore surface an increase in water and BSA flux is observed as well as a decrease in BSA rejection due to collapse of the chains. This work highlights the versatility of selectively grafting polymer chains containing a superparamagnetic nanoparticle from specific membrane locations. Depending on the frequency of the oscillating external magnetic field membrane properties may be tuned for a specific separation.