In Situ Small‐Angle X‐ray Scattering Investigation of the Formation of Dual‐Mesoporous Materials

Abstract

The formation of a 2D-hexagonal (p6m) silica-based hybrid dual-mesoporous material is investigated in situ by using synchrotron time-resolved small-angle X-ray scattering (SAXS). The material is synthesized from a mixed micellar solution of a nonionic fluorinated surfactant, R(F) 8 (EO)9 (EO=ethylene oxide) and a nonionic triblock copolymer, P123. Both mesoporous networks, with pore dimensions of 3.3 and 8.5 nm respectively, are observed by nitrogen sorption, transmission electron microscopy (TEM), and SAXS. The in situ SAXS experiments reveal that mesophase formation occurs in two steps. First the nucleation and growth of a primary 2D-hexagonal network (N1), associated with mixed micelles containing P123, then subsequent formation of a second network (N2), associated with micelles of pure R(F) 8 (EO)9 . The data obtained from SAXS and TEM suggest that the N1 network is used as a nucleation center for the formation of the N2 network, which would result in the formation of a grain with two mesopore sizes. Understanding the mechanism of the formation of such materials is an important step towards the synthesis of more-complex materials by fine tuning the porosity.

Thermal and Hydrothermal Stability of Hierarchical Porous Silica Materials

“…The SAXS patterns show the presence of 3 peaks for the un‐calcined dual‐mesoporous material. As reported previously, the first (11.2 nm) and second (6.2 nm) peaks correspond to the (100) and (110) reflections, respectively of the hexagonal structure of the matrix that is templated by the P123‐riched micelles and the third peak corresponds to the (100) reflection of the hexagonal structure of the matrix templated by the fluorinated‐rich micelles , . It should be noted that this peak and the (200) reflection of the network induced by the P123‐riched micelles overlaps.…”