Kinetics of Formation of Micelle-Templated Silica Mesophases Monitored by Electron Paramagnetic Resonance

Time-Resolved in Situ Raman and Small-Angle X-ray Diffraction Experiments: From Silica-Precursor Hydrolysis to Development of Mesoscopic Order in SBA-3 Surfactant-Templated Silica

“…In addition, experimental synthesis conditions must be adapted to meet EPR apparatus requirements: use of either flat cells or tubes imply smaller reaction volumes where no stirring is available making this setup unsuitable for a number of established experiments. In some cases 15 , this aspect does not seem to really matter since stirring is replaced by temperature effect on material formation, as it occurs in material synthesis under hydrothermal conditions. DLS: dynamic light scattering is seldom used to follow evolution of overall micellar size during self-assembly process, as ref.…”

“…Such technique, extensively used by the groups of Goldfarb 14 and Galarneau-Ottaviani, 15 can be considered as being truly time-resolved due to its very high sensitivity even with a low amount of paramagnetic species. As far as in-situ approach is concerned, introduction of an external probe with a paramagnetic center brings an extra parameter to take into account.…”

“…Later in the '90s, several interesting studies put in evidence a self-assembling phenomenon between silicates and surfactant micelles and this was possible using in situ techniques, but after preventing the silicate species from extensive condensation. Firouzi et al 28 used NMR and neutron scattering techniques to show the formation of cylindrical micelles from spherical one upon silicate addition to the starting solution; Galarneau et al 15 used EPR in presence of well-chosen paramagnetic probes to prove that an exchange between silicate anions and surfactant counter-ion occurs at the micelle double layer interface while Frasch et al 17 , by mean of fluorescent techniques showed that ion exchange is quite limited at the micellar double layer interface but it is rather enhanced when the surfactant molecule is alone in solution. Micelles only play a role of surfactant reservoirs rather than "building blocks" of the whole structure.…”

Molecular Dynamics Simulation of the Early Stages of the Synthesis of Periodic Mesoporous Silica

“…Using Cryo-TEM, Regev 16 observed a sphere-to-rod transition upon addition of silica, eventually leading to the formation of clusters of cylindrical micelles. On the other hand, Galarneau et al 17 concluded that silicates promoted the formation of irregular aggregates of spherical micelles. They suggested that a gradual transition from spheres to cylinders took place within those aggregates by an Ostwald ripening process, eventually forming a hexagonal liquid crystal.…”

Ordered Porous Nanomaterials: The Merit of Small

“…Despite the large variety of mechanisms that have been proposed to explain the formation of these materials, and even from numerous recent experiments carried out by Electronic Paramagnetic Resonance [179,180] and measurements made with probe molecules [181], it has become clear that, as it happened with zeolites, the interaction between the inorganic precursor and the template molecule is the key factor to control the mesostructure of the final material. Nevertheless, the exact stage at which these interactions come into play is still under debate and seems to largely depend on the synthesis conditions.…”