Azo-Containing Polymer Brushes: Photoalignment and Application as Command Surfaces

Abstract

A brush polymer containing photosensitive mesogenic side chains has been directly synthesized on glass substrates by a grafting method involving polymerization of a metacrylic azobenzenic monomer under Atomic Transfer Radical Polymerization (ATRP) conditions. Brush polymer surfaces, with respect to more traditional films, are resistant to solvents and to high temperatures due to the covalent bonds between chain and substrate, which stabilizes the film morphology. The peculiar characteristics of the present polymeric brushes, namely the intrinsic in-plane orientation of the mesogenic units located in the side chains, together with the possibility of a fine control on the structure, make them very attractive for application as command surfaces.

We then employed such brushes as photo-controllable command surfaces in twisted/planar switchable cells filled with a low molecular weight liquid crystal and we characterized the molecular order at interface by means of confocal polarized Raman microscopy.

Keywords:

• ATRP
• azobenzene
• confocal polarized Raman spectroscopy
• optical command surface
• polymeric brush
• polymeric liquid crystals

Acknowledgments

This work has been financially supported by MIUR (PRIN 2007) and University of Bologna (CLUSTERCAT-Strategic project 2006).