Pressure-induced ionic liquid crystal in 1-dodecyl-3-methylimidazolium tetrafluoroborate

Abstract

The phase behaviors of 1-dodecyl-3-methylimidazolium tetrafluoroborate ([C12MIM][BF4]) had been investigated by means of Raman spectroscopy and polarized optical microscopy under pressure values up to 2.0 GPa at the temperature of 80.0 °C. Upon compression, change in the ratio of peak heights of symmetric and asymmetric CH2 stretching modes of Raman spectra in [C12MIM][BF4] (r(CH2)ss/(CH2)as) indicated that it might experience two successive phase transitions. The structure evolution of the sample, which was investigated through the image analysis from polarized optical microscopy, was found to share many of the known quantitative properties of the smectic A phase of [C12MIM][BF4]. These facts were suggestive of ionic liquid crystal induced by compression in [C12MIM][BF4] under the pressure between 0.25 GPa to 0.60 GPa, which was similar to ionic liquid crystal upon cooling from its melt.