Characterization of graft-modified porous polymer membranes

Porous poly(vinylidene fluoride) membranes were graft modified with acrylic acid by radiation-induced grafting utilizing electron beam. When the grafted membranes were characterized by the measurements of convective permeability, diffusion, and ion exchange properties, the membranes showed properties of variable permeability membranes with respect to the permeability of solvent and the ionic semipermeability. The permeability for the studied membranes (extent of grafting varied from 0 to 93 wt %) can be controlled by the ionic strength and pH of the permeate. The more grafted the membranes are the greater are the changes in the permeability; e.g., for the extent of grafting of 85 wt % the permeability increases ca. 4 orders of magnitude when the electrolyte concentration is increased from 10 mM to 1 M. The membranes with the extent of grafting of ca. 10 wt % or more appeared to have equal charge density on the pore walls resulting in the same cation transference number.