The role of the ionic liquid C₆C₁ImTFSI in the sol–gel synthesis of silica studied using in situ SAXS and Raman spectroscopy

Abstract

The sol-gel synthesis of a silica based ionogel using the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C6C1ImTFSI) as the solvent has been followed in situ by combined μ-focused X-ray scattering and μ-Raman spectroscopy. By covering the momentum transfer range 0.2 < q < 30 nm(-1) we probe the evolution of the characteristic peaks of the ionic liquid, associated with the existence of polar and non-polar domains, as a function of reaction time. Our detailed analysis of the small angle X-ray scattered (SAXS) pattern reveals that the nano-structure of the ionic liquid is partially retained during the sol-gel synthesis, as indicated by the broader yet distinguishable SAXS signatures. We also observe that the signature associated with the non-polar and polar domains shift to higher and lower q-values, respectively. Interestingly, this behavior correlates with the evolution of the chemical composition of the sol as probed by Raman spectroscopy. More precisely, we observe that both the nano-structural changes and the production of polar molecules arrest at the point of gelation. This is rationalized by the tendency of the reagents and products of the sol-gel reaction to locate in different portions of the nano-structure of the ionic liquid.

Sol-gel synthesis pathway and electrochemical performance of ionogels: A deeper look into the importance of alkoxysilane precursor

“…The weak bands appearing at 854 and 739 cm -1 in the MTMS spectrum correspond to the rocking vibrations of CH3 group in Si−CH3 29 . The Raman bands associated with FA (shown here in Figure 1e) have been reported in the past 16,30,31 . Similar to the Raman spectra of the alkoxides discussed earlier, the weak band at 2958 cm -1 in FA Raman spectrum is assigned to the C−H stretching vibration.…”

“…The stretching vibrations of C−O in methyl formate (located at 909 cm -1 ) and O−CH3 in methanol (located at 1020 cm -1 ) are undetectable in the TMOS and MTMS-based ionogels' spectra. Depletion of various Raman peaks in the 1350-1450 cm -1 and 1600-1800 cm -1 regions are partially related to the consumption of FA as a result of carboxylation and esterification reactions 22,30,31 . In addition, the bending vibrations of C−H bonds present in methyl formate contribute to the Raman peaks in the 1440-1470 cm -1 region 22 .…”

First examples of organosilica-based ionogels: synthesis and electrochemical behavior

“…This is close to the conductivity of the pristine IL indicating that the confinement of the IL into a matrix does not significantly affect the conductivity [11,16–17]. Again using the same IL, Martinelli and coworkers have provided a set of interesting studies on how the ion flexibility and dynamics affect the conductivity in silica nanoparticle-based IGs and related systems [18–22]. Horowitz and Panzer synthesized mechanically compliant silica-based IGs.…”

“…These parameters enable the tuning of the IL loading, the IL/matrix ratio, and in some cases also the tuning of the IL behavior by tailoring the interactions of the IL with the wall of the silica [36,57]. Indeed, several research groups have provided different approaches towards silica-based IGs [11,16–18 22,24–25]. The main issue with most of these materials is that they cannot withstand mechanical stress and there is thus a need for stabilizing silica IGs for, e.g., flexible devices.…”

Facile Preparation of Biocompatible and Transparent Silica Aerogels as Ionogels Using Choline Dihydrogen Phosphate Ionic Liquid

“…Further, the silica gel matrix consists of agglomerated silica nanoparticles [84]. The increase in scattering intensity of the peak in the lower q range is due to the formation of more silica networks with respect to ionic liquid content [85].…”