Surfactants hexagonal array

The other type of porous glass that has cylindrical pores is mesoporous silicate (MPS) (14,15). The advantage of MPS is in its feasibility to make a small pore diameter, typically below 10 nm. A columnar-phase liquid crystal, formed from surfactant molecules with a long alkyl chain tail and silicate molecules, is calcined to remove hydrocarbons. At the end, a hexagonal array of straight and uniform cylindrical holes is created in a crystalline order. MPS is not available commercially either. 

Figure 4.4. Preparation of MTS materials. The diagram shows self assembly of the surfactant into micelles followed by condensation of silica around the micelles. The micelles arrange themselves into an approximately hexagonal array. After the formation of the silica around the micelles, the micelles are burnt out, leaving pores where the micelles were. The pores are an accnrate reflection of the size and shape of the micelles. This makes the pores uniformly sized and shaped.

Fig. 77. Schematic drawing of the liquid-crystal templating mechanism. Hexagonal arrays of cylindrical micelles form (possibly mediated by the presence of silicate ions), with the polar groups of the surfactants (light grey) to the outside. Silicate species (dark grey) then occupy the spaces between the cylinders. The final calcination step burns off the original organic material, leaving hollow cylinders of inorganic material [473]...

In summary, nanometer-sized mesoporous silica and alumina spheres with tunable diameters (80 - 900 nm) can be synthesized in organic solvent. Mesoporous silica spheres templated by cationic surfactant (CTAB) have hexagonal array with monodispersed pore size (-2.4 nm), high surface areas (-1020 m2/g), and pore volume (1.02 cm3/g). Mesoporous alumina spheres templated by amphiphilic triblock copolymer show a large disordered mesopore (10.0 nm) and high BET surface area (360 m2/g). 

The original reaction mechanism for the growth of M41S and MCM-41 materials was proposed by Mobil researchers. 1 This proposed mechansim involved formation of rod-like structures of micelles and concomitant formation of a hexagonal array of rods, after which an inorganic species would encapsulate the rods and surround the surfactant species. Calcination of these composite materials led to the... 

Q.S. Huo, R. Leon, P.M. Petroff, and G.D. Stucky, Mesostructure Design with Gemini Surfactants. - Supercage Formation in a 3-Dimensional Hexagonal Array. Science, 1995, 268, 1324-1327. 

Huo, Q. et al., Mesostructure design with gemini surfactants supercage formation in a three-dimensional hexagonal array. Science, 268, 1324, 1995. 

A hexagonal array of mesopores was observed, probably templated locally by the CTAB segregated from the surfactant mixture (see Figure 11.4, upper part). The calcined product (designated as ZSU-38) gave a BET surface area of 863 m g". ... 

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