The influences of the spacer of gemini surfactants on the structure of silicic mesoporous materials

Gemini surfactants, with two quaternary ammonium head groups separated by a spacer with variable configurations and with each head group attached to a same or different hydrophobic tail, can be used to control the packing parameter and the organic polycharge centers. By this means, the structure of mesoporous material prepared using surfactant template can be considerably controlled by changing the structures of Gemini surfactant, especially the characteristics of the spacer. The flexibility and the hydrophilicity of the spacer can be changed by varying the length of methylene chain of spacers from 3C to 12C, or adopting phenyl and hydroxyl radicals. These deduced successful synthesis of series of ordered mesoporous structure. When the length of methylene spacer chain of template was between 4C similar to 8C, hexagonal mesoporous materials were produced, while cubic mesoporous materials were obtained when the length of spacer chain was 10C similar to 12C. It is shown that the GEM16-6-16 and GEM16-12-16 were effective templates for highly ordered MCM-41 and MCM-48 respectively. The GEM16-3(OH)-16, which introduced a hydrophilic flexible hydroxyl radical to the spacer, produced less ordered sandwich structure. The GEM16-(1-Ar-1)-16, with a hydrophobic rigid spacer of p-xylyl, was hard to dissolved in water. When ethanol was used as cosolvent, hollow sphere materials were produced. The samples were characterized by XRD, TEM, and N-2 adsorption-desorpotion.