Journal of the Electrochemical Society vol:154 issue:11 pages:D598-D611
The incorporation of particles in electrodeposited coatings strongly depends on the surface properties of these particles. It is shown that hydrophilic particles do not incorporate due the presence of a hydration layer on their surface. This hydration layer prevents
hydrophilic particles from making “real” contact with the electrode and hence particles and electrode remain separated by a small gap. During metal deposition, metal ions diffuse into this gap and are reduced on the electrode underneath the particle. This causes the particles to be pushed up by the moving metal/electrolyte interface, instead of incorporating in the growing metal deposit. This phenomenon is called “riding” and the extent to which particles ride depends on the hydrophilicity of the particles and on parameters which govern the diffusion of metal ions in the gap. It is shown that riding of hydrophilic particles can be suppressed by applying an external pressure on the hydration layer which destabilizes this layer. However, even in absence of an external pressure, destabilization of the hydration layer occurs if the metal grows more or less conformally around the particle. This is due
to the increase of attractive surface forces with metal deposit thickness. Atomic force microscopy pull-off measurements of
partially incorporated particles show that a critical deposit thickness is needed to incorporate a particle irreversibly. The critical deposit thickness decreases with increasing hydrophobicity of the particle.