Photo-responsive azo-functionalised flexible polymer substrate for liquid crystal alignment

ABSTRACT

An azobenzene derivative containing a dimethylchlorosilane end group was chemically attached to a flexible polymer substrate to create permanent photo alignment layer. The commercially obtained polymer substrate (overhead projector film) was characterised and found to contain cellulose acetate as the main component. Surface functionalization of the substrate was confirmed through X-ray photoelectron spectroscopy (XPS), attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy, water contact angle (CA) and atomic force microscopy (AFM) techniques. Photo-isomerisation behaviour of the azo-layer on the polymer substrate was additionally confirmed by UV-diffuse reflection spectroscopy (UV-DRS). Further, the azo-modified flexible substrate was analysed for the orientation of the bulk liquid crystal (LC) sample and tuning the LC orientation by utilising photo-switching behaviour of the azo-layer on the substrate.

Graphical abstract

KEYWORDS:

• Polymer substrate
• surface functionalisation
• azobenzene
• photo-isomerisation
• alignment
• homeotropic

Acknowledgments

S.U. acknowledges the Science and Engineering Research Board (SERB), Department of Science and Technology, New Delhi [Grant No.ECR/2015/000419] for funding through Early Career Research award. B.S. thanks SERB, New Delhi for financial support. K. M. acknowledges MHRD-RUSA 2.0 for the fellowship. Authors also thank MHRD-RUSA 2.0, Department of Education, New Delhi [Letter No. F. 24/51, 2014-U] and DST-PURSE-II, New Delhi for financial support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Science and Engineering Research Board (SERB), Department of Science and Technology, New Delhi [Grant No. ECR/2015/000419] for the financial support.