Binding of ionic surfactants to charged polymer brushes grafted onto porous substrates

A polymer brush containing a sulfonic acid group was appended onto the pore surface of a porous hollow-fiber membrane about 1 mm thick. During the permeation of a N-alkylpyridinium chloride (CnPyCl; n=4, 12, and 16) solution, the feed concentration of which ranged from 0.10 to 500 mM, through the pores at a constant transmembrane pressure of 0.2 MPa, C12PyCl was bound to the charged polymer brush. Prepermeation of a magnesium chloride solution through the pores was effective in regaining the liquid permeability via ionic crosslinking of the charged groups with the magnesium ion at a degree of crosslinking of 54%. The charged polymer brush captured C12PyCl without releasing the magnesium ion. At a surfactant concentration of about 70% of its critical micelle concentration, the equilibrium binding capacity of the charged polymer brush started to decrease due to micelle formation. In contrast, C4PyCl and PyCl without micelle formation increased the equilibrium binding capacity with increasing concentration while expelling the magnesium ion.