title: Effects of a protic ionic liquid on the reaction pathway during non-aqueous sol-gel synthesis of silica: a Raman spectroscopic investigation.
abstract: 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.
authors.affiliation: Department of Chemical and Biological Engineering, Chalmers University of Technology, Kemivägen 4, 41296 Göteborg, Sweden. anna.martinelli@chalmers.se.
authors.forename: Anna
authors.initials: A
authors.lastname: Martinelli
mesh_terms: D005782:Gels / Q000737:chemistry*; D006868:Hydrolysis; D052578:Ionic Liquids / Q000737:chemistry*; D012822:Silicon Dioxide / Q000138:chemical synthesis / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
chemical_list: D005782:Gels; D052578:Ionic Liquids; D012822:Silicon Dioxide
references.citation: Phys Rev Lett. 2005 Aug 12;95(7):075505
references.pmid: 16196794
references.citation: Chem Soc Rev. 2011 Feb;40(2):907-25
references.pmid: 21180731
references.citation: Phys Chem Chem Phys. 2012 Oct 14;14(38):13216-23
references.pmid: 22910853
references.citation: Langmuir. 2012 Dec 18;28(50):17477-93
references.pmid: 23214421
references.citation: Soft Matter. 2014 Aug 14;10(30):5618-27
references.pmid: 24965195
references.citation: J Phys Condens Matter. 2010 Jan 20;22(2):025401
references.pmid: 21386252
references.citation: Chem Rev. 2013 Aug 14;113(8):6592-620
references.pmid: 23782155