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Electroconvection and Pattern Formation in Nematic Liquid Crystals

Acharya, Gyanu R.
http://rave.ohiolink.edu/etdc/view?acc_num=kent1239804049

Abstract Details

2009, PHD, Kent State University, College of Arts and Sciences / Department of Physics.
Electrohydrodynamic convection (EHC) in nematic liquid crystals is a crucial model system for the study of spontaneous, non-equilibrium pattern formation in anisotropic systems. To characterize the EHC patterns, I have utilized two nematic samples: 4-ethyl-2-fluoro-4'-[2-(trans-4-n-pentylcyclohexyl)-ethyl]-biphenyl (I52) and a mixture of 65 wt.-% p-butyl-p'-methoxy-azoxybenzene and 35 wt.-% p-ethyl-p'-methoxy-azoxybenzene (Phase 5), filled in standard planar cell. In I52, over certain range of the conductivity, the initial transition leads to two families of counter-propagating oblique modes that loose stability at onset. This is consistent with a stability analysis of the EHC equations, which predict a Hopf bifurcation with four oblique critical wave numbers. The critical voltage, the wave vectors and the Hopf frequencies are measured at different controlled parameters. These experimental observations are in agreement with the standard model and weak electrolyte model of electroconvection. Time evolution of spatial Fourier transform (FT) of a series of these images taken under same controlled parameters are studied using two-wave demodulation technique to extract envelopes. The temporal variation of the amplitudes of these envelopes is periodic between zig and zag modes which is consistent with the theoretical predictions. To study spatiotemporal chaos (STC), four-envelopes of the pattern are extracted by applying 2D spatial Fourier transform and 1D temporal Fourier transform. The temporal variation of the amplitudes of these envelopes is chaotic in space and time. Localized states called ‘worms’ are in existence for another set of parameters at higher frequencies in the conduction regime. In Phase 5, I observed oblique stationary (OS) modes at lower frequencies and normal traveling (NT) modes at higher frequencies during electroconvection. Discontinuous jump in the Hopf frequency is observed from zero to over 20 rad/s as the driving frequency is increased along the threshold curve in the conduction regime. Measurements of the wave vector components also exhibit an abrupt jump in their values at the OS to NT transition regime.
James Gleeson, Dr. (Committee Chair)
David Allender, Dr. (Committee Member)
Brett Ellman, Dr. (Committee Member)
Oleg Lavrentovich, Dr. (Committee Member)
229 p.
Fluid Dynamics; Physics
Nematic liquid crystals; Electroconvection; Hopf frequency; Spatiotemporal chaos; Four-wave demodulation

Recommended Citations

Citations

  • Acharya, G. R. (2009). Electroconvection and Pattern Formation in Nematic Liquid Crystals [Doctoral dissertation, Kent State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=kent1239804049

    APA Style (7th edition)

  • Acharya, Gyanu. Electroconvection and Pattern Formation in Nematic Liquid Crystals. 2009. Kent State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=kent1239804049.

    MLA Style (8th edition)

  • Acharya, Gyanu. "Electroconvection and Pattern Formation in Nematic Liquid Crystals." Doctoral dissertation, Kent State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1239804049

    Chicago Manual of Style (17th edition)

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© 2009, all rights reserved.
This open access ETD is published by Kent State University and OhioLINK.