Mesopore constrictions derived from the substitutionally co-packed SBA-15

Abstract

A highly ordered, substitutionally co-packed, bimodal hexagonal mesoporous silica, ORK-1, with a dual mesopore/constriction size distribution has been synthesized successfully by the co-packing of two different copolymer micelles (amphiphilic triblock copolymer systems) in strong acid media. The materials have a similar but constricted channels (as shown by transmission electron microscopy, powder X-ray diffraction, TGA and N 2 adsorption isotherm (BET)) to those of SBA-15 materials. However, real-time UV–Vis absorbance spectra confirm the strongest intra-micellar interaction of two types of copolymer molecules in a binary system occurs when the molar content of these copolymers are equal, i.e. P123:P65 = 0.5:0.5. The stronger the interaction between these copolymers, the shorter the gelation (packing) time is. Both the size and the distribution of the mesopores/constrictions can be adjusted by varying the molar ratio between the surfactants. The size distribution of pores ‘templated’ by the surfactant micelles has been proved to depend on the relative concentrations of the two block copolymers. In particular, the higher the concentration fraction of one of the block copolymers in the solution the larger is the micelles formed there from and so the greater the diameter of the derived pore size in the bimodal porous structure. The lower the concentration fraction of the block copolymer, the smaller the micelles (associated with that copolymer) and the smaller the pore diameter. A mechanism for the formation of these materials is discussed. Evidence suggests that these interacted copolymer surfactants have significant influence on their sol–gel properties and the final mesostrucures.