Study of the Initial Formation Stages of the Mesoporous Material SBA-15 Using Spin-Labeled Block Co-polymer Templates

Abstract

The hexagonal, silica-based, mesoporous material SBA-15 is prepared using poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) block co-polymer (Pluronic P123, PEO20−PPO70−PEO20) as a template and tetramethyl orthosilicate (TMOS) as a silica source. This work focuses on the investigation of its formation on the molecular level, with emphasis on the early stages of the reaction, when the interaction between silica precursors and the Pluronic micelles occurs. This was achieved using in situ X-band electron paramagnetic resonance (EPR) spectroscopy, in combination with electron spin−echo envelope modulation (ESEEM) experiments of Pluronic spin probes with different PEO and PPO chain lengths. In these Pluronic spin probes, the nitroxide spin label is located at the end of the PEO chain, which places them at different regions of the micelles. In the Pluronic micelles, the PPO chains define a hydrophobic region that is referenced as the core, whereas the more-hydrophilic PEO chains form the corona re...