Submicron coating of SiO2 nanoparticles from electrophoretic deposition

Anodic electrophoretic deposition (EPD) of SiO2 nanoparticles is investigated for the formation of submicron coatings. The deposition yield is studied relative to the nature of the working electrode (platinum, silicon wafer) implying de facto some different applied voltage range, the deposition time and the nanoparticle concentration. The composition of the films and the thickness of the deposited material are analyzed by energy dispersive X-ray spectroscopy through X-film software. The kinetic deposition and also the deposition mechanisms are discussed. For short deposition times, the linear Hamaker relation fits the experimental results, which implies that the migration-coagulation step would be the initial deposit mechanism of the silica nanoparticles. For long deposition times, the thickness of the film reaches a saturation value that is dependent on the applied electric field. This phenomenon is mainly due to an increase in the deposit resistance. For low applied voltage, the adhesion and the cohesion of the film obtained by EPD are clearly enhanced by comparison with simple dip-coating. Thin solid films, nearly uniform and crack-free up to 300 nm of thickness, are obtained by optimization of the EPD parameters. For high applied voltages, some electrochemical reactions occur towards electrodes during EPD and disturb the deposition of nanoparticles, which limits the final thickness.