T. Jimbo et al., Characterization of an amphoteric-charged layer grafted to the pore surface of a porous membrane, LANGMUIR, 14(25), 1998, pp. 7112-7118
Porous membranes having amphoteric charge groups were prepared by heterogen
eous graft polymerization from aqueous solution containing acrylic acid and
(N,N-dimethylamino)propyl acrylamide. The charging properties of the ampho
teric charge groups grafted to the pore surface were investigated by zeta p
otentials obtained from streaming potential measurements. Theoretical devel
opment in terms of the amphoteric pore surface was attempted by introducing
a site dissociation model of ps-dependent zeta potentials. The theoretical
model is based on the assumption that the surface charge arises only from
the protonation and deprotonation of the charged surface groups exposed to
electrolyte solution. Good fits between experimental results and theoretica
l equations were attained, and thereby the isoelectric point, dissociation
constant, apparent surface site density, and acid-to-base ratio of the amph
oteric pore surface were determined. Depending on the variation in the feed
monomer ratio for graft polymerization, these parameters correspondingly c
hanged. If we assumed that the acid-to-base ratio of the amphoteric pore su
rface corresponds to that in the whole membrane, the net charge density of
the membrane quantitatively obtained from the potentiometric titration gave
the respective charge densities of acidic and basic groups using the acid-
to-base ratio determined from the site dissociation model. Here we proposed
an approach to characterize the amphoteric-charged pore surface by the pH-
dependent zeta potential and its theoretical modeling.