In this experiment we focused on the technique of electrophoresis mediated sedimentation, which has revealed to be useful in better structuring than simple gravitational sedimentation. This is due to the fact that electrophoresis both speeds up the process and diminishes the appearance of defects through mesoscopic electrohydrodynamics [M. Böhmer. Langmuir 12 (1996) 5747] [M. Trau et al. Langmuir 13 (1997) 6375] [Y. Solomentsev et al. Langmuir 13 (1997) 6058] [W.D. Ristenpart et al. Phys. Rev. E 69 (2004) 021405]. The interesting novelty we put in, was based on the following hypothesis: A more or less laminar macroscopic flow in the deposition cell could (in some experimental conditions) improve the quality of the deposited colloidal crystals.

Our experimental set-up was designed in order to get a von Kármán-like flow. The one we obtained was some kind of a swirling flow which dampens as approaches the deposition substrate (due to the viscous boundary layer). This allows the colloidal particles to better adjust to a site.

The main experimental problem concerned to the elimination of the continuous phase of the colloidal dispersion. Even though we applied a high potential to fix the particles to their positions, partially (during the application of the high voltage) more particles deposited. Also, when the liquid was removed, could be some rearrangements of particles as well as in the drying stage.

Summarizing, we observe an improvement of the colloidal crystals quality. The success is related on the fact of having more than one privileged direction in the deposition process. The primary direction is perpendicular to the substrate (gravity and electrophoresis), while the secondary ones promote the ordered arrangement of the colloidal particles

• • M. Yoldi et al. Proceedings of 6^th ICTON, 1 (2004) 330

  • M. Yoldi et al. J. Mater. Sci. 41 (2006) 2965

  • M. Yoldi. Ph.D. thesis. Universidad de Navarra (2008)

  • M.C. Arcos. Ph.D. thesis. Universidad de Navarra (2008)

This work was partly supported by PIUNA, and by Spanish Ministry of Science (refs. BFM2002-02011, MAT2003-02369). M. Yoldi acknowledges MECD scholarship and M.C. Arcos acknowledges "Gob. de Navarra" scholarship