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Abstract
This work reports the effect of dye on the photopolymerisation and electro-optical properties of polymer dispersed liquid crystal (PDLC) composite films. Dichroic PDLC (DPDLC) films based on a photocurable polymer and nematic liquid crystal (LC) with an azo dichroic dye were prepared by photopolymerisation-induced phase separation method. Polarising optical microscopy has been used for monitoring the phase separation kinetics and two-phase morphology evolution in the DPDLC system. LC domains with radial structures during initial period of phase separation adopted a resultant morphology of bipolar configuration over the course of polymerisation. The phase separation and morphology of LC domains was found to be dependent on the amount of dye used. Moreover, the addition of small amount of dye reduced the switching voltage, and enhanced the contrast ratio with improved switching time in the PDLC films. It was shown that, under the application of an electric field, the molecular orientation and absorbance of dichroic dye can be controlled in DPDLC to induce non-linearity and colour contrast without the use of polarisers.
Acknowledgements
The authors are grateful to Prof. K.K. Raina for helpful discussions and Dr. Pankaj Kumar for his technical assistance during the research work. We thank E. Merck, Japan for providing the LC material. One of the authors (Manoj Malik) would like to thank University Grants Commission (UGC), INDIA for financial assistance through UGC-SAP program. This work was supported by a grant from AICTE, INDIA (vide research grant no. 8023/BOR/RID/RPS-05/9/10).