Controlled permeability and ion exclusion in microporous membranes functionalized with poly(L-glutamic acid)

The functionalization of materials with polyamino acids provides opportunities where electrostatic and conformational properties can be utilized for selective separations and controlled transport applications. The influence of covalently attached poly(L-glutamic acid) (PLGA) on the performance characteristics of a microporous cellulosic support has been investigated to determine its effect on the transport of water and charged solutes. The presence of these charged multifunctional groups promotes electrostatic interactions with ionic species far removed from the pore surface. This allows for nonsteric ion exclusion involving membrane materials that offer less resistance to solvent (water) transport. In addition, the helix-coil transitions of this polypeptide and "core leakage" effects have been shown to affect both the permeability and solute retention in a reversible fashion upon variations in the solution pH. Following PLGA attachment, the permeability could be adjusted from 50 to 90% of the value of the base support matrix (∼3-6 × 10^-4 cm³/cm²s bar). Experiments were performed on single and mixed electrolyte systems using model inorganic and organic solutes. Solute rejection values as high as 73% were reported for dilute Na₂SO₄ solutions using membranes with pore sizes ranging from 0.05 to 0.21 μm.