(263c) Responsive Membranes for Advanced Separations

Stimuli responsive membranes have been developed for many applications some of the original being controlled release of drugs.  Stimuli responsive membranes change their physical properties in response to changes in their environmental conditions such as pH, ionic strength and temperature or due to changes in external field due to photo-irradiation or changing electric and magnetic fields.  Changes in physical properties of the membrane in response to changed environmental conditions can lead to changes in the mass transfer and interfacial properties of the membrane.  Today stimuli responsive membranes find many potential applications.

Often, in membrane based separation processes the properties of the membrane surface that contact the feed stream can have a significant effect on membrane performance.  For example, membrane surface properties have been shown to affect the rate of fouling during processes such as microfiltration, ultrafiltration, nanofiltration and reverse osmosis.  Modifying just the membrane surface has the potential to retain the properties of the bulk membrane material but modify the interactions between components of the feed and the membrane surface.  Here we have developed responsive membranes by surface modification. Two examples will be discussed in this presentation

We have developed novel, magnetically responsive membranes.  Magnetically responsive nanobrushes have been grafted to the barrier surface of commercially available nanofiltation membranes.  In an oscillating magnetic field, movement of the magnetically responsive nanobrushes leads to suppression of concentration polarization resulting in higher permeate fluxes and better rejection during filtration.  In addition, we have grafted magnetically responsive nanorbrushes to the pore surface of track etched microfiltration membranes. Movement of the nanobrushes can lead to changes in pore size and hence change the rejection properties of the membrane.  These novel magnetically responsive membranes could lead to a new class of fouling resistant membranes for separation applications.

In the second example we have developed responsive membrane for hydrophobic interaction chromatography.  Poly N-vinylcaprolactam (PVCL) chains were grown from the surface of regenerated cellulose membranes using atom transfer radical polymerization (ATRP).  PVCL is a thermo-responsive polymer with a lower critical solution temperature (LCST) that depends on the concentration of salt ions present in solution. The LCST decreases below room temperature in buffer containing 1.8 M (NH₃)₂SO₄ where the polymer adopts a more hydrophobic/collapsed conformation.  At low ionic strength, the LCST remains above room temperature. Adsorption and desorption of bovine serum albumin (BSA) and immunoglobulin G (IgG) have been investigated.  Loading was conducted in high ionic strength buffer.  Elution was conducted in low ionic strength buffer.  By using a responsive ligand that changes its conformation during loading and elution, high protein recoveries were obtained.  Ligands that respond to solution ionic strength show promise for high performance hydrophobic interaction chromatography.