Effect of high electric fields on the nematic to isotropictransition in a material exhibiting large negative dielectric anisotropy |
| |
Authors: | S. Dhara N. V. Madhusudana |
| |
Affiliation: | (1) School of Physics, University of Hyderabad, Hyderabad, 500046, India;(2) Raman Research Institute, C.V. Raman Avenue, Bangalore, 560080, India |
| |
Abstract: | We report the experimental high electric field phase diagram of a nematic liquid crystal which exhibits a large negative dielectric anisotropy. We measure simultaneously the birefringence (Δn) and the dielectric constant (epsilon⊥) at various applied fields as functions of the local temperature of an aligned sample. We also measure the higher harmonics of the electrical response of the medium. The following experimental results are noted: (i) enhancement of orientational order parameter S in the nematic phase due to both the Kerr effect and quenching of director fluctuations; (ii) enhancement in the paranematic to nematic transition temperature (TPN) with field; (iii) divergence of the order parameter susceptibility beyond the tricritical point as measured by third harmonic electrical signal; (iv) a small second harmonic electrical signal which also diverges near TPN, indicating the presence of polarised domains. Our measurements show that ΔTPN(= TPN(E)-TNI(0)) varies linearly with |E| whereas the Landau de Gennes theory predicts a dependence on E2. It is argued that the quenching of director fluctuations by the field makes the dominant contribution to all the observations, including the thermodynamics of the transition. |
| |
Keywords: | 64.70.Md Transitions in liquid crystals 61.30.Gd Orientational order of liquid crystals electric and magnetic field effects on order 61.30.Dk Continuum models and theories of liquid crystal structure |
本文献已被 PubMed SpringerLink 等数据库收录! |