Abstrait

Broad temperature range blue phases in polymer dispersed cholesteric liquid crystals

Anita Kanwar, Sureshchandra J.Gupta

‘Blue phasesÂ’ (BP) in liquid crystal are three-dimensional cubic defect structures normally observed in chiral liquid crystals. These phases exist for very short duration of temperature from0.5°C to2°C. It is because of this restriction their practical usability is limitedwhich is proved both theoretically and experimentally. There are three well-known thermodynamically stable blue phases, BP III, BP II and BP I. BP III is amorphous with a local cubic lattice structure in the director field, whereas BP II and BP I have a fluid threedimensional periodic structure in the director field with simple cubic and body-centred cubic symmetry, respectively[1]. We have made polymer dispersed cholesteric liquid crystals (PDCLCs) with different concentrations of nematic and cholesteric liquid crystals in our lab using thermally induced phase separationmethod.We are reporting presence of broad temperature range blue phases in PDCLCs. Their presence is confirmed by various techniques viz. fabry parot scattering studies (FPSS), optical polarising microscope (OPM) and differential thermal analysis (DTA).We propose that the unusual behaviour of these blue phase materials is due to the addition of polymer to the cholesteric liquid crystals making them polymer dispersed cholesteric liquid crystals (PDCLCs)[2].