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 (pHiep) with an increased ionic strength. All salts had an equal dependence on the ionic strength. The pHiep 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 (pHiep), particularly in high (10−1 M) and low (10−3 M) MF electrolyte dispersions. No clear trend could be found for the pHiep dependence on the anion HSAB scale.

Graphical abstractAlthough the effect of simple electrolytes on the ζ-potential is indistinguishable when plotted as a function of ionic strength, the relative effect of anions could be identified when the isoelectric point is plotted against the HSAB, Hofmeister, and Born scales, respectively. The influence of cations remained, however, unseparable.Figure optionsDownload full-size imageDownload as PowerPoint slide