Electrokinetic behavior of melamine-formaldehyde latex particles at moderate electrolyte concentration

The electrokinetic behavior of micrometer-sized melamine-formaldehyde latex particles in 10^-3-10^-1 M monovalent electrolyte dispersions was investigated by electrophoresis and electroacoustics. Specific adsorption of the electrolytes was identified as a shift of the isoelectric point (pH_iep) with an increased ionic strength. All salts had an equal dependence on the ionic strength. The pH_iep was correlated with the anion sequence predicted by the hard-soft acid-base (HSAB) principle, Hofmeister series, and Born charging. The Born and the Hofmeister anion scale were successful in producing a systematic dependency of the isoelectric point (pH_iep), particularly in high (10^-1 M) and low (10^-3 M) MF electrolyte dispersions. No clear trend could be found for the pH_iep dependence on the anion HSAB scale.