Low density ionogels obtained by rapid gellification of tetraethyl orthosilane assisted by ionic liquids

Abstract

A non-hydrolytic one pot sol-gel method has been used to synthesize mesoporous silica ionogels with the confined ionic liquid (IL) 1-ethyl 3-methyl imidazolium tetra fluoro-borate [EMIM][BF 4]. The precursor for obtaining the SiO 2 matrix was tetraethyl orthosilicate (TEOS) and formic acid was used as a catalyst. These ionogels have been characterized by density measurements, TEM, BET, DSC, TGA and FTIR. The incorporation of the ionic liquid [EMIM][BF 4] enhances the gellification rate which results in the ionogels having very low density (∼0.3 g cm -3). The low density has been explained on the basis of the creation of 'blind embedded pores' in the matrix (apart from open pores) due to very rapid gellification (∼1 min). Morphological studies provide experimental evidence for the presence of blind pores/voids inside the ionogel ingots. We have also shown that the IL entrapped in nanopores (∼7-8 nm pore size) of the SiO 2 matrix has different physical properties than the bulk IL viz. (a) the phase transition temperatures (T g, T c and T m) of the IL change upon confinement, (b) the thermal stability reduces upon confinement, and (c) the pore wall interaction with the IL results in changes in the C-H vibrations of the imidazolium ring and alkyl chain (the former increasing) which is also indicated in our DFT-calculation. © 2012 The Royal Society of Chemistry.