Percolation View of Novolak Dissolution. 7. The Effect of Salts

The increase in dissolution rate brought about by the addition of salt to alkaline developers is caused by the difference in the diffusivities 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 anions to increase too. The faster OH- ions, which alone control the dissolution 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 mechanism. The retardation-of-dissolution effects that set in at high salt concentrations can be understood in terms of a competition of ions for the available percolation sites.