Pressure-driven transport of dilute electrolytes in microporous membranes containing terminally-anchored charged poly(amino acids) (PAA) has been investigated through both experimental characterization and model evaluation. The membrane pore structure was modified via single-point covalent attachment of either negatively (poly(L-glutamic acid) or PLGA) or positively-charged polypeptides (poly(L-arginine) or PLA and poly(L-lysine) or PLL) allowing for separations using microporous materials (i.e. cellulosic, silica/polyethylene composites). Thus, efficient exclusion of ionic species can be achieved in open membrane platforms with considerably lower pressure requirements than conventional NF. For instance, the solute rejection of 0.5 mM solutions of environmentally-toxic species, such as divalent oxyanions of As(V) and Cr(VI), using a PLGA functionalized silica support (pore size ∼100 nm) was >80% at 0.7 bar. The effects of solute type, concentration, pH, polypeptide loading and pore coverage of the attached macromolecule on the observed solute rejection and hydraulic permeability have been examined. In addition, immobilization of PLGA allows for conformation-based alteration of membrane separation properties upon changes in pH. These morphological transitions were investigated through application of permeability data to a two-region pore model describing solvent transport. This allows for theoretical evaluation of the effective thickness of the polypeptide-containing pore region. Ion transport was then modeled using a two-dimensional approach based on the extended-Nernst Planck equations coupled with Donnan equilibrium principles. The required parameters are the effective membrane surface charge density and the PAA pore coverage as determined through permeability studies. This analysis allows for evaluation of the fixed membrane charge density based on solute rejection data, as well as, estimation of the electrostatic properties of the immobilized poly(amino acids) (i.e. pK a shifts, pH dependent thickness of polymer containing pore region).
|Number of pages||15|
|Journal||Journal of Membrane Science|
|State||Published - Aug 1 2004|
Bibliographical noteFunding Information:
The authors recognize the NSF-IGERT program for the partial support of this research work. Thanks are also due to the US EPA STAR Nanotechnology Program for additional funding of this project.
- bacterial cellulose
- poly(L-glutamic acid)
- poly(amino acid)
ASJC Scopus subject areas
- Materials Science (all)
- Physical and Theoretical Chemistry
- Filtration and Separation