A dynamic broadened reflection band was achieved when a weakly polymer stabilized cholesteric liquid crystal containing a negative dielectric anisotropy nematic was subjected to a low DC field (< 3V/�m). The broadening effect was significant as the notch bandwidth enlarged symmetrically up to 3 times from its original value. A seven fold increase in bandwidth was observed for 22 mm thick cells which contained LCs with small birefringence (~0.04). The broadening effect is proportional to the strength of the applied DC field and relaxes to the original bandwidth when the DC field is removed. Fields, greater than a critical value cause a blue shift of the broadened band. The cholesteric mixture consisted of the chiral dopant S811, the negative dielectric LC ZLI-2079, 5% LC diacrylate monomer RM257 and 0.05% of UV initiator Irgacure 369. The weakly polymer stabilized network was formed by UV curing. Monomer concentrations were varied from 2 to 10 percent by weight showing best performance at concentrations of about 5 percent. The response times were on the order of ~10 secs and the relaxation ~ 2 secs. Addition of small amounts of a less viscous chiral dopant Limonene significantly reduced the response times. Different mechanisms for the broadening effects will be discussed to experimental results.

Dynamic reflection notch broadening in polymer stabilized cholesteric liquid crystals

245th National Meeting (2013)

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