Director field of birefringent stripes in liquid crystal/nanoparticle dispersions

Abstract

The thermal stability, alignment and electro-optic properties of liquid crystals can be fundamentally altered by dispersing small amounts of solid nanoparticles in a liquid crystal host. In the present study, the local alignment of the liquid crystal in such dispersions is studied by means of polarising optical microscopy and fluorescence confocal polarising microscopy. The results of two- and three-dimensional imaging indicate that birefringent stripes, which are induced by the presence of nanoparticles, correspond to twist disclinations that are located at the liquid crystal–substrate interface. The luminescence of dispersed semiconductor quantum dots shows that the ends of disclination threads are pinned to conglomerates of nanoparticles, which stabilise these line defects.

Keywords:

• liquid crystals
• nanocrystals
• disclinations
• fluorescence confocal polarising microscopy

Acknowledgements

The authors would like to thank Alexander Lorenz for his kind assistance with photography (Figure 1). Financial support by the Deutsche Forschungsgemeinschaft (DFG, KI 411), the European Science Foundation (ESF-EUROCORES, SONS II program, LCNANOP project), the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Technology Transfer Office (TTO) of the University of Manitoba for an IPM grant is gratefully acknowledged. BK would like to thank NSERC for an USRA.