The experimental part of this work was done in the laboratory of Dr. E. Görnitz at the Institute for Applied Polymer Research, Gölm (Germany). The vertical deposition technique [A.S. Dimitrov et al. Langmuir 12 (1996) 1303] [P. Jiang et al. Chem. Mater. 11 (1999) 2132] is based on the deposition of colloidal particles through capillarity when a contact line is moved along the substrate. We used the variant which consists in letting evaporate the continuous phase of the colloidal dispersion. We focused on improving the quality of crystal minimizing cracks by controlled sedimentation, evaporation and drying.

The experimental set-up is very simple and consists in a vial where the latex was put in, together with the substrate (glass). The whole system was placed in a temperature controlled device. The samples were obtained from latexes of various colloidal particles concentrations and at different temperatures.

In order to control sedimentation (for large particles at low temperatures), heavy water was added to the dispersion to obtain a better density matching between the colloidal particles and the continuous phase. It was observed in this case that the maximum average size of domains (in number of particles) lies on the same curve as the smaller particles do. On the other hand, to control evaporation we changed the volatility of the medium by adding ethanol to it. In that way we found the curve of average size of domain vs. ethanol fraction. Finally, we proved that the quality of crystals can be improved by adding water-miscible, but not volatile, liquids (as for example, glycerol) in small amounts. In that way, the colloidal crystal remains stable without drying completely, and thus avoiding the formation of cracks in the process.

• • M. Yoldi et al. Mat. Sci. Eng. C-Bio. S. 28 (2008) 1038.

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

We acknowledge to Dr. J. Wagner for fruitful discussions. We are indebted for technical support in polymerization to K. Schauer and to Dr. M. Pinnow for S.E.M. This work was partly supported by PIUNA, and by Spanish Ministry of Science (refs. BFM2002-02011, MAT2003-02369). M. Yoldi acknowledges MECD scholarship.