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Int. J. Mol. Sci. 2014, 15(4), 6488-6503;

Effects of a Protic Ionic Liquid on the Reaction Pathway during Non-Aqueous Sol–Gel Synthesis of Silica: A Raman Spectroscopic Investigation

Department of Chemical and Biological Engineering, Chalmers University of Technology, Kemivägen 4, 41296 Göteborg, Sweden
Received: 16 March 2014 / Revised: 25 March 2014 / Accepted: 31 March 2014 / Published: 16 April 2014
(This article belongs to the Special Issue Ionic Liquids 2014 & Selected Papers from ILMAT 2013)
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The reaction pathway during the formation of silica via a two-component “non-aqueou” sol-gel synthesis is studied by in situ time-resolved Raman spectroscopy. This synthetic route is followed with and without the addition of the protic ionic liquid 1-ethylimidazolium bis(trifluoromethanesulfonyl)imide (C2HImTFSI) in order to investigate its effect on the reaction pathway. We demonstrate that Raman spectroscopy is suitable to discriminate between different silica intermediates, which are produced and consumed at different rates with respect to the point of gelation. We find that half-way to gelation monomers and shorter chains are the most abundant silica species, while the formation of silica rings strongly correlates to the sol-to-gel transition. Thus, curling up of linear chains is here proposed as a plausible mechanism for the formation of small rings. These in turn act as nucleation sites for the condensation of larger rings and thus the formation of the open and polymeric silica network. We find that the protic ionic liquid does not change the reaction pathway per se, but accelerates the cyclization process, intermediated by the faster inclusion of monomeric species. View Full-Text
Keywords: ionic liquids; silica; ionogels; sol-gel; Raman spectroscopy ionic liquids; silica; ionogels; sol-gel; Raman spectroscopy

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Martinelli, A. Effects of a Protic Ionic Liquid on the Reaction Pathway during Non-Aqueous Sol–Gel Synthesis of Silica: A Raman Spectroscopic Investigation. Int. J. Mol. Sci. 2014, 15, 6488-6503.

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