Bent-core liquid crystal-functionalised flexible polymer substrates for liquid crystal alignment

ABSTRACT

A transparent flexible polymer film is chemically functionalised with a bent-core liquid crystal (BCLC) compound for effective alignment of the bulk BCLC sample at the substrate–LC interface. The surface attachment was achieved via a simple procedure which involved pre-treatment of the polymer film (commercial name: over head projector film) using piranha solution followed by chemically attaching the BCLC compound through silane condensation reaction. Surface characterisation of the unmodified and BC-modified flexible films was carried out through X-ray photoelectron spectroscopy (XPS), attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy, contact angle (CA) and atomic force microscopy (AFM) techniques. The BC-modified flexible substrates are analysed for their efficiency to orient the bulk LC sample. Remarkably, the chemically modified polymer substrates are highly efficient in vertically aligning both the BC and rod-like LC samples at the substrate–LC interface, in comparison to their unmodified counterparts. The described method is simple, reproducible, surface modified substrates are highly stable and more importantly reusable. The demonstrated method for the alignment of BCLCs advances a step forward towards the realisation of applications proposed for these fascinating compounds.

GRAPHICAL ABSTRACT

KEYWORDS:

• Flexible polymer substrate
• surface functionalisation
• bent-core
• nematic
• vertical alignment

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. 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. Special thanks to NIT, Trichy, India for helping with DSC and SASTRA Deemed University, Thanjavur, India for helping with XPS analysis.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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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.