Nonionic fluorinated surfactant:: Investigation of phase diagram and preparation of ordered mesoporous materials

The behavior of fluorinated surfactant F(CF2)(8)C2H4(OC2H4)(9)OH in water solution was investigated, and the preparation of mesoporous molecular sieves was achieved. A direct micellar phase (L-1) and a hexagonal (H-1) liquid crystal were found. Small-angle X-ray scattering measurements proved that the hydrophobic chains are completely extended and that the cross sectional area remains constant in H-1. At 80 degreesC, materials with a hexagonal array of their channel are prepared via a cooperative templating type mechanism in a wide range of surfactant concentrations (5-20 wt %). Decreasing the hydrothermal temperature leads to the formation of wormhole-like structure. In this case the channel arrangement is no longer governed by the surfactant behavior but by the silica condensation and polymerization. An increase of the mean pore diameter with heating temperature is noted. This result is associated with changes of aggregation number with temperature. A comparison of the characteristics of the materials obtained with both hydrogenated and fluorinated surfactants is also made.