Gemini surfactants material

The preparation of pure silica MCM-48, using cationic gemini surfactants, followed by a controlled extraction of the surfactant results in materials that have a more narrow pore size distribution than the ones in which the surfactant is removed by calcination. Since no calcination is needed, there is no unit cell contraction and the extraction surfactant can be recrystallized and re-used. 

Use of mixture of surfactant (e.g., C18-3-1 and CTAB for MCM-41, Gemini surfactant mixture for MCM-48) as template and post-synthesis hydrothermal treatment.[1] This method can give high-quality and large-pore mesoporous silica materials. 

The ability of siloxane surfactants to stabilize different chemical reactions allows the preparation of different nano-materials. For example, gemini surfactants containing a siloxane moiety have been used as templates for the preparation of mesopoious metal oxides sueh as zirconium, titanium, and vanadium oxides. The siloxane segment seems to play an important nano-propping role during the surfactant removal by direct calcination [105]. 

Arguably the most important parameter for any surfactant is the CMC value. This is because below this concentration the monomer level increases as more is dissolved, and hence the surfactant chemical potential (activity) also increases. Above the CMC, the monomer concentration and surfactant chemical potential are approximately constant, so surfactant absorption at interfaces and interfacial tensions show only small changes with composition under most conditions. For liquid crystal researchers, the CMC is the concentration at which the building blocks (micelles) of soluble surfactant mesophases appear. Moreover, with partially soluble surfactants it is the lowest concentration at which a liquid crystal dispersion in water appears. Fortunately there are well-established simple rules which describe how CMC values vary with chain length for linear, monoalkyl surfactants. From these, and a library of measured CMC values (35-38), it is possible to estimate the approximate CMC for branched alkyl chain and di- (or multi-) alkyl surfactants. Thus, most materials are covered. This includes the gemini surfactants, a new fashionable group where two conventional surfactant molecules are linked by a hydrophobic spacer of variable length (38). 

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