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Abstract
The decrease in Goldstone mode relaxation frequency with applied dc electric field in a deformed helix ferroelectric liquid crystal (DHFLC) is observed at room temperature. This decrement in relaxation frequency is observed at very low dc electric fields (below the threshold voltage, i.e. around 2 V). This behaviour is compared with that of conventional ferroelectric liquid crystals (FLCs) where the relaxation frequency increases with the applied dc electric field. It is observed that a low dc electric field is insufficient to unwind the helix completely due to the higher rotational viscosity of the DHFLC material. Moreover, the DHFLC molecules take more time in the winding (Smectic C–Smectic C∗) process, compared to the FLC molecules, which take comparatively less helix winding time because of their low viscosity. The decrease in relaxation frequency in DHFLCs with bias has been attributed to the critical balancing amongst the electric torque, elastic constraints and rotational viscosity in a certain regime of the electric field not exceeding the threshold field.
Acknowledgements
The authors sincerely thank Dr Vikram Kumar, Director, National Physical Laboratory, for continuous encouragement and interest in this work. We sincerely thank Dr S.S. Bawa, Dr Indrani Coondoo, Mr Amit Choudhary and Ms Anu Malik for fruitful discussions. We are grateful to Dr Poonam Silotia of the University of Delhi, India for useful discussions. The authors AK and JP are grateful to UGC, New Delhi and CSIR, New Delhi, respectively, for financial assistance.