New photosensitive polymer composites based on oriented porous polyethylene filled with azobenzene‐containing LC mixture: reversible photomodulation of dichroism and birefringence

Abstract

A new type of polymer–liquid crystal (LC) composite with photovariable dichroism and birefringence is described. Porous stretched polyethylene (PE) films with pores size in the range 50–500 nm were used as polymer matrices. A photochromic cholesteric mixture based on a commercial nematic mixture doped with azobenzene and merocyanine dopants was prepared. Highly birefringent deeply coloured flexible films possessing strong dichroism were obtained by introduction of the photochromic LC mixture into the stretched PE films by capillary forces. UV irradiation leads to E–Z isomerisation of azobenzene‐containing molecules inside the composite films and results in a significant decrease of the dichroism almost down to zero due to isothermal transition from the mesophase to isotropic melt stimulated by the isomerisation process. This process is reversible and the visible light irradiation or annealing lead to a back transition to the uniaxial birefringent and dichroic state. The composite films show a high fatigue resistance during the alternating cycles of the UV–visible irradiation. These novel composites can be considered as promising materials for photonics and optical information processing.

Keywords:

• polymer–liquid crystal composite
• reversible photomodulation
• dichroism
• birefrigence

Acknowledgements

This research was supported by the Russian Foundation of Fundamental Research (08‐03‐00481) and Program COST‐D35.