See also:
Liquid crystalline phase of an imidazolium room-temperature ionic liquid
Nematic liquid crystalline phase of 5CB (35.4 C)
Room-temperature ionic liquids
Our work on room temperature ionic liquids (RTILs) is carried out in collaboration with a number of international research groups. At Glasgow University, we apply femtosecond optical Kerr effect (OKE) spectroscopy using two laser set-ups giving access to time delays from 15 fs to 8 ns. The time traces are Fourier transformed to produce reduced Raman spectra in a frequency range from 125 MHz (0.004 cm-1) to about 10-30 THz. No other research group has such a great range of frequencies combined with our signal dynamic range of about six orders of magnitude.
Dielectric spectra are assembled from three pieces. Our collaborators Richard Buchner (University of Regensburg, Germany) and Glenn Hefter (Murdoch University, Australia) take dielectric relaxation spectra from 200 MHz to about 100 GHz. Our collaborator Markus Walther (University of Freiburg, Germany) takes time-domain terahertz spectra (THz-TDS) from ~0.1 to 3 THz. Finally, we have used a far-infrared FTIR spectrometer to take spectra from 1 THz to 20 THz. These three types of spectra are bolted together using the Kramers-Kronig equation.
The Raman and dielectric spectra are in principle the same, that is, they have the same components but with different amplitudes. In RTILs, we have found that the spectra are significantly different. The cause of these differences is mesoscopic (supramolecular) structure in these liquids. In relatively recent work (JACS 131, 11140 (2009)), we demonstrated the presence of micellar like clusters in small alkyl tail 1,3-dialkylimidazolium-based RTILs. In our latest work we are observing subtly different structure in protic ionic liquids (Faraday Disc. in press).
We are now studying a range of RTILs in collaboration with Ken Seddon (Queen's University, Belfast) and his colleagues. The work now extends to RTILs with long tails that have liquid-crystalline and similar states.
Figure: OKE (black) and dielectric loss, ε" (red) data for ethylammonium nitrate (EAN) at 25 °C (the relative amplitude scaling is arbitrary). For more details, see "Structure and dynamics in protic ionic liquids: A combined optical Kerr-effect and dielectric relaxation spectroscopy study, Faraday Disc. in press.