The increase in dissolution rate brought about by the addition of salt
to alkaline developers is caused by the difference in the diffusiviti
es of the OH- ions of the base and the anions of the salt. Adding salt
increases the flux of cations into the film, allowing the flux of ani
ons to increase too. The faster OH- ions, which alone control the diss
olution of the resin film, benefit more from this opportunity than the
salt anions. The base ions appear to diffuse about 5-10 times faster
than the other anions, which suggests that OH- ions do not migrate by
free volume diffusion but rather by a Grotthus-type proton transfer me
chanism. The retardation-of-dissolution effects that set in at high sa
lt concentrations can be understood in terms of a competition of ions
for the available percolation sites.