In vertical deposition of colloids, there are important parameters which need to be tuned in order to fabricate homogeneous colloidal crystals. Of many, the concentration is one of the most relevant; which is neither homogeneous nor constant along the whole experiment. Under certain conditions [M. Giuliani et al., Phys. Rev. E 79 (2009) 032401] [R. Shimmin et al., Langmuir 22 (2006) 6507], particles accumulate near the contact line in a region called particle pool zone (PPZ). The morphology formed depends on the local concentration in the PPZ, rather than on the initial concentration. M. Giuliani et al. [M. Giuliani et al., Phys. Rev. E 79 (2009) 032401] reported the dynamics of the contact line for diluted colloids in a vertical deposition configuration by measuring the characteristic speed of contact line. Also they explained the direct correlation between the obtained morphology (dried particles) and its corresponding speed of contact line.

In the research presented here, we characterized the effects that D.C. electric fields have in the vertical deposition of colloids. Our experimental way of proceeding is similar to previous experiments [M. Giuliani et al. Phys. Rev. E 79 (2009) 032401].

We applied a weak DC field to control the local region near the contact line (PPZ), comparing it to the previously studied case without electric fields [M. Giuliani et al., Phys. Rev. E 79 (2009) 032401]. We measure the speed of contact line as the fluid phase evaporates and the colloidal structure is deposited. The applied electric field has an influence on the colloidal dispersion via electrophoresis, which increases or decreases the particle concentration near the depositing zone. The effect induces a concentration gradient along the direction of the applied field which affects the morphology of the dried deposit of colloidal particles. As a result, the applied field has an effect on the receding contact line through morphological formation and its transition.

• • M. Giuliani & M. Pichumani et al. Eur. Phys. J. ST 192 (2011), 121.

  • M. Giuliani, Ph.D. thesis. Universidad de Navarra (2010)

  • M. Pichumani, Ph.D. thesis. Universidad de Navarra (2012)

This work was partly supported by the Spanish Government (ref. FIS2008-01126) and by Departamento de Educación (Gobierno de Navarra). M. Giuliani and M. Pichumani acknowledge partial financial support from the "Asociación de Amigos de la Universidad de Navarra".

Morphologies (summary) of the dried deposits of colloidal particles. A - Vertical sparse stripes (VSS) at 0.1%, B - Non compact morphology (NC) at 0.3%, C - Non compact dense morphology (NCD) at 0.5%, D - Compact monolayer (CM) at 0.5%, E - Multilayer (ML) followed by sparse deposit at 0.5%, F - Vertical column multilayer (VCM) at 0.5% (width of image is 6 mm). Scale bars are 25 μm and the magnifications are different:

Characteristic speeds of the contact line for each initial concentration at different applied voltages. For a given condition, in most cases, two characteristic speeds were measured (squares and circles):