C. Filiâtre

Electrodeposition of particles at nickel electrode surface in a laminar flow cell

Abstract Electrodeposition of polystyrene particles on a nickel electrode was observed in the laminar flow cell. The efficiency (rate) of the electrodeposition was determined depending on flow intensity, electrode polarization vs. Ag/AgCl electrode and ionic strength of the solution. The negative polystyrene latex particles were turned positive by adsorption of cetyl trimethyl ammonium bromide (CTAB) and experiments were performed at fixed concentration of the surfactant. It was found that at the CTAB concentration 5×10−5 mol dm−3 mostly single particles were deposited. It was observed that during the experiment, particles were deposited at a constant rate, which well correlated with the electrode polarization and their zeta potential. When the experiments were performed at various flow conditions in the laminar flow cell, the rate of deposition was found only weakly dependent on the flow intensity. That indicated that the hydrodynamic blocking effects were negligible under conditions encountered in the experiment. It was confirmed by the simulation of the dependence of the hydrodynamic blocking on the shear rate in the simple shear flow. At higher concentration of CTAB 5×10−4 mol dm−3 and for the electrode polarization of −1.5 V (vs. Ag/AgCl), transient aggregation at the electrode surface was observed. Qualitative aspects of this aggregation are presented. When the electrode polarization was removed the aggregates moved away except the initial ones, which were firmly attached to the surface. The observed phenomena can be explained in terms of clustering of particles by electrokinetic flows.

Electrodeposition of latex particles in the presence of surfactant: Investigation of deposit morphology

The deposition of micrometric latex particles on a polarized nickel surface was investigated using a laminar flow cell equipped with a video assembly used to observe and record particle behavior near the electrode. The effects of the nature of the counterions and the concentrations of surfactants on the deposit structure were studied. Negative polystyrene latex particles were turned positive by adsorption of cetyltrimethylammonium in the form of different salts: bromide (CTAB), chloride (CTAC), and hydrogenosulfate (CTAHS). Image analysis was used to gain information on the mechanisms of particle deposition on the electrode. At CTAB concentration 5x10(-5)M, mostly single particles were deposited on the electrode and their adhesion was irreversible. The adsorption mechanism was shown to be dependent on the succession of electrophoretic migration and attractive particle-surface interactions. At a higher CTAB concentration (5x10(-4)M) a transient 3D aggregation was observed which was attributed to electroosmotic and electrohydrodynamic phenomena in the vicinity of the electrode. In the presence of CTAC, aggregates were formed on the electrode for both concentrations. In the case of CTAHS the deposition rate was very low in comparison with CTAB and CTAC. This result was explained by the lower zeta potential of the particles with respect to the other cases. The formation of the aggregates was reversible; furthermore, their morphologies were strongly dependent on the kind of counterion. The aggregates formed in CTAB solution were dense while more open structures were observed with CTAC.