Conformational States of Ionic Liquid 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide in Bulk and Confined Silica Nanopores Probed by Crystallization Kinetics Study

Abstract

The nonaqueous sol-gel process has been used to synthesize the ionogels by confining ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; [EMIM][TFSI]) into silica gel matrices. The present study is concerned mainly with probing the conformational states of the IL ([EMIM][TFSI]) through crystallization kinetics study of the bulk and confined ionic liquid (IL) in nanopores of silica matrix. The crystallization kinetics has been studied by the isothermal method using differential scanning calorimetry (DSC). For bulk IL, DSC result shows three crystallization peaks due to different conformations of IL molecules. DSC results show that one of these crystallization peaks disappears upon confinement due to interaction of IL molecules with the silica pore wall surfaces. The crystallization kinetics of bulk and confined IL is quantified using the Avarami analysis. Confinement of IL results in a decrease of the Avarami exponent, indicating one-dimensional crystal growth. To support the results obtained from crystallization kinetics study, investigate the properties of confined IL, and to study the morphological properties of silica gel matrices, some other characterization techniques, viz. TGA, XPS, FTIR, BET, SEM, and TEM, have been used. The XPS and FTIR results show the change in the binding energy of constituents of IL molecule and vibrational bands related to IL, respectively. BET, SEM, and TEM analyses display the uniform pore structures in IL confined silica matrices. © 2015 American Chemical Society.