Enhanced stability of the columnar matrix in a discotic liquid crystal by insertion of ZnO nanoparticles

Abstract

An experimental characterisation of dispersions of ZnO nanoparticles (NPs) in the columnar matrix of a discotic liquid crystal has been carried out. Thermophysical properties have been investigated by absorbance spectroscopy, differential scanning calorimetry, polarising optical microscopy, dielectric measurements, dc conductivity, X-ray diffraction and infrared (IR) dichroism technique. The experimental results show that inclusion of ZnO NPs into the columnar matrix enhances the orientational order in the columnar phase and does not affect the two-dimensional hexagonal lattice. The alignment in homeotropic samples is also found to be better with the addition of the NPs. The real (ϵ′) and imaginary parts (ϵ′′) of the permittivity increase by a small amount in the dispersions. The order parameter measured using the IR dichroism technique in the face-on geometry (homeotropic alignment) shows an enhancement for the composite system. The dc conductivity is also found to increase by an order of magnitude by addition of the NPs. These results suggest an improved stacking of the disc-like molecules within the columns by the insertion of the ZnO NPs possessing high charge mobility. Such composite systems would be highly beneficial for potential applications such as organic conductors.

Keywords:

• columnar phase
• liquid crystal–nanoparticle composites
• orientational order
• dielectric properties

Acknowledgements

The authors are very grateful to Professor V. Lakshminarayanan for providing the facility to measure dc conductivity of the samples and to Suvratha Krishnamurthy for resynthesising of the DLC.