Crystallization kinetics behavior of ionic liquid [EMIM][BF4] confined in mesoporous silica matrices

Abstract

The crystallization kinetics behavior of pure ionic liquid (IL) (1-ethyl-3-methylimidazolium tetrafluoro borate; EMIMBF₄) as well as IL confined in mesoporous silica matrices (termed as ionogel) is the concern of our present study. The ionogels (IGs) were synthesized by a non-hydrolytic sol–gel process. DSC was employed to investigate the isothermal crystallization kinetics behavior of IL in bulk as well as in confinement. Isothermal crystallization temperatures were chosen a few °C above the onset crystallization temperature of IL in bulk and in confinement. Crystallization kinetic parameters such as relative crystallinity (α), crystallization half time (t_1/2), crystallization rate constant (K) and Avrami exponents (n) have been determined by an isothermal technique using DSC. Crystallization kinetic parameters have been found to be dependent on the amount of IL and the crystallization isothermal temperatures. The experimental data based on the isothermal method show that confinement of the IL results in (i) delayed crystallization and (ii) reduced dimensionality of the crystallization kinetics from 3D (for bulk IL) to 1D. X-ray photoelectron spectroscopy (XPS) and transient plane source (TPS) studies have been used to explain the delayed crystallization.