PREPARATION OF MODEL POLYVINYL TOLUENE) LATTICES AND CHARACTERIZATION OF THEIR SURFACE-CHARGE BY TITRATION AND ELECTROPHORESIS

A set of monodisperse model poly(vinyl toluene) latices was prepared in the presence of sodium dodecyl sulfate as an emulsifier, with particle radii varying from 0.04 to 0.08 μm and with a constant surface charge density of about 0.5 to 0.6 μC/cm2 arising solely from the complete and pH-independent dissociation of strongly attached sulfate groups. Surface tension measurements indicated that the adopted purification procedure removed all the emulsifier from the continuous phase. A quick and novel microelectrophoretic technique used for the determination of the electrokinetic characteristics of these very small latices involved the determination of the electrophoretic mobilities of a strongly scattering substrate covered with a layer of adsorbed latices, as has been used for biomacromolecules. Results of such experiments were compared with those obtained from extremely time-consuming conventional moving-boundary experiments. Determinations of ψ0 ( eψ0 kT ∼ 2) of these latices by ion exchange and subsequent titration and of ψζ from electrophoresis show that for these model latices ψ0 ≈ ψζ, indicating the absence of a Stern layer. The low surface potential and the absence of a Stern layer indicate that the latex systems can be used as ideal Gouy-Chapman model colloids. © 1979.