Formation Mechanism of Mesostructure Liquid-crystal Template and Cooperative Self-assembly

2 Formation Mechanism of Mesostructure Liquid-crystal Template and Cooperative Self-assembly 

Establishing a mechanistic understanding is needed for better control of the synthesis process. A better understanding of the formation mechanism via combined characterization techniques and modeling may lead to a more rational approach for tuning the pore structure of mesoporous materials. 

The main difference between the synthesis of MCM-41 mesoporous material and traditional synthesis of zeolite or silica molecular sieve is the use of different templates. An individual organic molecule or metal cation is used for the traditional synthesis of silica microporous molecular sieve. For example, the typical template for ZSM-5 synthesis is tetrapropylammonium ion the crystal is formed through the condensation of silicate species around the template molecule, while for the formation of MCM-41, the typical template is the assembly of large molecules containing one hydrophobic chain with more than 10 carbons. 

The formation of lyotropic liquid-crystal mesophase depends on the structure and properties of surfactant, solvent, and reaction conditions. Although studies on lyotropical liquid crystals have been carried out for many years, the structure and properties of some mesophases are still not very clear. Since lyotropic liquid crystals rely on a subtle balance of intermolecular interactions, it is difficult to analyse their structures and properties, the boundary in the phase diagram may be not accurate and the minor phase may be missed. 

However, there are different ways to describe the details of the cooperative self-assembly of the surfactant and the silicate species. The two mechanisms proposed by Davis[61,66] and Stucky[8] are most noteworthy. 

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