Temperature dependence in the synthesis of hexagonal MSU-3 type mesoporous silica synthesized with Pluronic P123 block copolymer

MSU-type mesoporous silica prepared with nonionic surfactants according to the two-step pathway, exhibits a specific feature that makes its structure sensitive to the synthesis temperature. Until now, this factor had been demonstrated to affect the pore structure in the mesoporous range, between 2 and 5 nm. We describe in the present report that this parameter affects drastically syntheses of MSU-3 silica made with the block copolymer Pluronic 123 within a temperature range of 5–75 °C. Depending on the synthesis temperature, the pore size can vary from microporous (below 2 nm) to mesoporous (close to 9 nm) in a steady-like evolution. However, two properties of block copolymers must be addressed for a full understanding of this evolution: the solubility limit of nonionic templates at higher temperatures, which prevents the formation of micelles because a too high hydrophobicity, and the Critical Micelle Temperature (CMT) at lower temperatures, which prevents the formation of micelles because a too high hydrophilicity. These results confirm that the assembly mechanism that leads to mesostructured materials requires a fine balance of interactions, not only between inorganic and organic reagents but also between the organic templates themselves. [Copyright &y& Elsevier]