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.