Fine silica powder modified with quaternary ammonium groups 2. The influence of electrolyte and pH

Abstract The zeta potential and the mean particle size of fine silica powder modified with quaternary ammonium groups having alkyl chains of various lengths (-N + (C m H 2m + 1)(CH 3 ) 2 , m =4, 6, and 8 were measured as a function of pH or electrolyte concentration in suspensions. The zeta potentials of the modified fine silica powder as a function of pH constantly showed positive values at pH 2–10. XN4–8 did not show any isoelectric point. The zeta potentials were independent of while the mean particle sizes were dependent on the number of carbon atoms in the alkyl chains. In the presence of various electrolytes, the coagulation concentration increased in the following order: Fe(CN) 6 3− 4 2− 3 − − Further, the dispersion-coagulation of the modified fine silica powder was analyzed using Derjaguin-Landau-Verwey-Overbeek (DLVO) theory.