Influence of the remanent polarisation on the liquid crystal alignment in composite films of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and a cyanobiphenyl-based liquid crystal

ABSTRACT

Polymer-dispersed liquid crystals (PDLCs) of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and nematic 4-cyano-4ʹ-n-hexylbiphenyl (6CB) or 4-cyano-4ʹ-n-pentylbiphenyl (5CB) were prepared to study the effect of the remanent polarisation of the polymer on the liquid crystal alignment. We measured the macroscopic alignment of the liquid crystal molecules in the thickness direction by means of Infrared Transition-Moment Orientational Analysis. Electrical poling at 100 V/µm caused an increased order parameter up to 0.15. After subsequent annealing above the nematic-to-isotropic phase-transition temperature, the order parameter was reduced to 0.02. Nevertheless, the order parameter was still higher than for non-poled film indicating a slight orientation in thickness direction. Both values are lower than those expected from model calculations. In agreement with dielectric measurements, we attribute this result to the shielding effect of mobile charge carriers within the liquid crystal inclusions.

GRAPHICAL ABSTRACT

KEYWORDS:

• Polymer-dispersed liquid crystal
• ferroelectric polymer
• remanent polarisation
• liquid crystal alignment

Acknowledgements

Financial support from the ‘Deutsche Forschungsgemeinschaft’ (DFG) within the project GE 945/9-1 is gratefully acknowledged. LH is indebted to Holger Müller (U Potsdam) for FTIR measurements. LH also thanks Monika Ehlert and Dr Peter Frübing (both U Potsdam) for their support with the DSC experiments. WK likes to thank ‘Build Mona – the Leipzig School of Natural Science’, the Sächsische Forschergruppe ‘FOR 877 From Local Constraints to Macroscopic Transport’ and the ‘Deutsche Forschungsgemeinschaft’ within the SFB TRR 102 for financial support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Deutsche Forschungsgemeinschaft [grant numbers GE 945/9-1, SFB TRR 102]; Sächsische Forschergruppe 877; Build Mona – the Leipzig School of Natural Science.