CHARACTERIZATION OF COLLOIDS BY MEASUREMENT OF THEIR MOBILITIES

The electrophoretic mobility of some colloids has been measured in var ious media, either by capillary electrophoresis or by laser Doppler ve locimetry. The two methods have first been tested on standard latex-po lystyrene solutions. They give comparable results, which show that the mobility of the polystyrene nanospheres depends essentially upon thei r charge/surface ratio. We have then determined the experimental condi tions leading to relatively stable suspensions of Th-3(PO4)(4) particl es. Under these conditions, difficulties arise in the separation of pa rticles from solution, and consequently in the solubility measurements of the thorium orthophosphate. Finally, the effects of the compositio n of the solution as well as of the colloid concentration on the chara cteristics (charge density, reactivity) of the colloidal species, have been outlined in the case of some mineral oxides of interest: SiO2, T iO2, Al2O3. Despite its higher selectivity, capillary electrophoresis appears less appropriate than Laser Doppler Velocimetry for characteri zing colloids in their natural medium, but can be useful as a compleme ntary method.