High ionic strength electrokinetics of melamine-formaldehyde latex

The electrokinetic potential of melamine-formaldehyde latex at high ionic strengths was measured by means of two different instruments. The present study confirms that the zeta potentials in 1 M 1-1 electrolyte solutions can be as high as +/-20 mV. The IEP of latex at low ionic strengths was at pH 11. The increase in the electrolyte concentration induced a shift in the IEP to low pH for all studied salts, and this indicates specific adsorption of the anions. The magnitude of the shift depends chiefly on the nature of the anion and increases in the series Cl < NO(3) = Br < I, and the nature of the cation (Li, Na, K, Cs) plays a rather insignificant role.