Electric field driven assembly of hybrid micelles for shaping of porous silica films

Abstract

The technological impact of porous structures in catalytic applications has stepped up the search for innovative shaping tools. A new approach to shape porous structures based on the assembly of hybrid micelles under the influence of a directional driving force, such as the electric field, is proposed in this work. The growth of silica porous coatings induced by electrophoresis has been explored. The electrophoretic deposition (EPD) of different cetyltrimethylammonium bromide (CTAB) solutions, a silica sol (SiO₂) and a hybrid sol (CTAB+SiO₂) has been studied in terms of the solution/sol conductivity, the electrophoretic mobility of the suspended species and the applied electric field and time. After the optimisation of the sol composition for EPD, the growth behaviour of the deposit has been determined by atomic force microscopy. Results evidence the assembly of hybrid micelles as a consequence of the synergism of two phenomena: the increase in the concentration of the micelles at the substrate surroundings and the silica sol gelling. Crack free silica porous films (0·4 mg cm⁻²) with a deposited mass per unit area one order of magnitude higher than those prepared by dip coating can be produced by EPD.

Keywords:

• Electrophoretic deposition
• Micelles
• Sol–gel
• Mesoporous silica
• Atomic force microscopy

Acknowledgments

This work has been supported by MINECO Spain under contract nos. MAT2009-14448-C02-01 and MAT2012-38650-C02-02. Authors acknowledge D. Sanchez for his useful help.