A spin probe study of mesoporous silica formation via a neutral templating route

The structure of dodecylamine (DDA) aggregates acting as templates in the synthesis of mesoporous silica (in the DDA/water/ethanol/tetraethoxysilane (TEOS) system) has been studied via the EPR spectra of a variety of spin probes and of a spin-labeled silica precursor. Two recipes have been examined:  one, starting from a water-rich DDA solution, A0, reported to produce a silica with framework mesopores and textural pores comparable in volume, and another, starting from an ethanol-rich solution, B0 which yields a solid having practically only framework pores. For both compositions the relative positions of the spin probes in the aggregates have been determined, the local polarities expressed in terms of the Kosower scale and their motions examined. The aggregates formed have been characterized as emulsion droplets for A0 and micelles with radii <25 A for B0. After reaction of A0 and B0 with TEOS, all probes showed significantly hindered motion in the wet precipitates. In the solid B, precipitated from the ...