Characterization of a nematic mixture by reversed‐phase HPLC and UV spectroscopy: an application to phase behaviour studies in liquid crystal–CO₂ systems

Abstract

In the present work a simple but selective reversed‐phase high performance liquid chromatographic method (HPLC) was developed for the analysis of the nematic liquid crystal mixture E7 to determine precisely the composition of the liquid crystal mixture used in PDLC film preparation. Ultraviolet absorption spectrophotometry experiments were carried out to determine the HPLC detection wavelength and to characterize the absorptivity constants of E7 constituents. The technique developed is applied in the case of equilibrium solubility studies for E7 in supercritical carbon dioxide (scCO₂). The results indicate unambiguously that scCO₂ can fractionate the mixture towards the E7 components. The four single component peaks of the E7 mixture were distinctively separated by this method, which enabled the determination of the solubility of E7 constituents in the scCO₂.

Acknowledgements

This work was supported by Fundação para a Ciência e Tecnologia through the projects POCTI/CTM/37435/2001, POCTI/CTM/47363/2002 and grant SFRH/BPD/11665/2002, and by FEDER and FSE.