Electrophoretic behavior of bare and polymer-coated latices

Polymer-stabilized latex dispersions find many applications but our underst anding of such suspensions is limited; data on well-characterized systems c an furnish needed insight. To provide this information, the behavior of bar e particles and particles coated with adsorbed poly(ethylene oxide) was inv estigated using electrophoretic mobility and photon correlation spectroscop y measurements. Bare particles show the typical maximum in mobility as a fu nction of salt concentration; adsorbed neutral polymer reduces the mobility and suppresses the features. Hydrodynamic size measurements indicate that the polymer layers are rather thick and almost completely occlude the diffu se charge. Nevertheless, the particles retain a significant electrophoretic mobility, indicating that the electrokinetic shear plane is located somewh ere inside the polymer layer. Comparing experimental results with those fi om an approximate theory for fuzzy particles indicates that the layer's pri ncipal effect is hydrodynamic.