Study of dipole dynamics and pre-transitional effects at isotropic to nematic phase transition by low-frequency dielectric relaxation measurements

A. K. George, Mariam Al-Hinai, D. M. Potukuchi, S. H. Al-Harthi, C. Carboni

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Abstract

Thermal microscopy (TM) as well as low-frequency (LF) dielectric relaxation studies are carried out on a nematic liquid crystal (NLC), viz E7 (Merck Ltd, UK). The isotropic to nematic (IN) transition temperature TIN determined by TM and LF-dielectric permittivity measurements agrees with the available data. Dielectric loss studies in the frequency region of 5-10 MHz indicate a relaxation (in the kHz region) akin to Debye type off-centered dispersion. The observed nematic relaxation is found to correspond to reorientation (about the short axis) of the nematic dipole to the external field. The temperature variation of the nematic relaxation frequency fR is found to follow an Arrhenius shift, with an activation energy of 1.7eV. Temperature variation of the dielectric strength (Δε = ε0) and the distribution parameter α in the nematic phase are discussed. The dynamic response of the nematic dipoles and growth of pre-transitional fluctuations are found to be nonlinear in the vicinity of the IN transition. The value of the exponent αeff= 0.072 indicates weak growth of transitional fluctuations across the IN transition.

Original languageEnglish
Pages (from-to)1037-1045
Number of pages9
JournalPhase Transitions
Volume76
Issue number12
DOIs
Publication statusPublished - 2003

Fingerprint

Dielectric relaxation
Microscopic examination
Phase transitions
Permittivity measurement
dipoles
low frequencies
Nematic liquid crystals
Dielectric losses
Superconducting transition temperature
Dynamic response
Activation energy
microscopy
Temperature
dynamic response
dielectric loss
retraining
transition temperature
liquid crystals
exponents
permittivity

Keywords

  • Dielectric permittivity
  • Dielectric relaxation
  • Nematic liquid crystal

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electronic, Optical and Magnetic Materials

Cite this

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abstract = "Thermal microscopy (TM) as well as low-frequency (LF) dielectric relaxation studies are carried out on a nematic liquid crystal (NLC), viz E7 (Merck Ltd, UK). The isotropic to nematic (IN) transition temperature TIN determined by TM and LF-dielectric permittivity measurements agrees with the available data. Dielectric loss studies in the frequency region of 5-10 MHz indicate a relaxation (in the kHz region) akin to Debye type off-centered dispersion. The observed nematic relaxation is found to correspond to reorientation (about the short axis) of the nematic dipole to the external field. The temperature variation of the nematic relaxation frequency fR is found to follow an Arrhenius shift, with an activation energy of 1.7eV. Temperature variation of the dielectric strength (Δε = ε0 -ε∞) and the distribution parameter α in the nematic phase are discussed. The dynamic response of the nematic dipoles and growth of pre-transitional fluctuations are found to be nonlinear in the vicinity of the IN transition. The value of the exponent αeff= 0.072 indicates weak growth of transitional fluctuations across the IN transition.",
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TY - JOUR

T1 - Study of dipole dynamics and pre-transitional effects at isotropic to nematic phase transition by low-frequency dielectric relaxation measurements

AU - George, A. K.

AU - Al-Hinai, Mariam

AU - Potukuchi, D. M.

AU - Al-Harthi, S. H.

AU - Carboni, C.

PY - 2003

Y1 - 2003

N2 - Thermal microscopy (TM) as well as low-frequency (LF) dielectric relaxation studies are carried out on a nematic liquid crystal (NLC), viz E7 (Merck Ltd, UK). The isotropic to nematic (IN) transition temperature TIN determined by TM and LF-dielectric permittivity measurements agrees with the available data. Dielectric loss studies in the frequency region of 5-10 MHz indicate a relaxation (in the kHz region) akin to Debye type off-centered dispersion. The observed nematic relaxation is found to correspond to reorientation (about the short axis) of the nematic dipole to the external field. The temperature variation of the nematic relaxation frequency fR is found to follow an Arrhenius shift, with an activation energy of 1.7eV. Temperature variation of the dielectric strength (Δε = ε0 -ε∞) and the distribution parameter α in the nematic phase are discussed. The dynamic response of the nematic dipoles and growth of pre-transitional fluctuations are found to be nonlinear in the vicinity of the IN transition. The value of the exponent αeff= 0.072 indicates weak growth of transitional fluctuations across the IN transition.

AB - Thermal microscopy (TM) as well as low-frequency (LF) dielectric relaxation studies are carried out on a nematic liquid crystal (NLC), viz E7 (Merck Ltd, UK). The isotropic to nematic (IN) transition temperature TIN determined by TM and LF-dielectric permittivity measurements agrees with the available data. Dielectric loss studies in the frequency region of 5-10 MHz indicate a relaxation (in the kHz region) akin to Debye type off-centered dispersion. The observed nematic relaxation is found to correspond to reorientation (about the short axis) of the nematic dipole to the external field. The temperature variation of the nematic relaxation frequency fR is found to follow an Arrhenius shift, with an activation energy of 1.7eV. Temperature variation of the dielectric strength (Δε = ε0 -ε∞) and the distribution parameter α in the nematic phase are discussed. The dynamic response of the nematic dipoles and growth of pre-transitional fluctuations are found to be nonlinear in the vicinity of the IN transition. The value of the exponent αeff= 0.072 indicates weak growth of transitional fluctuations across the IN transition.

KW - Dielectric permittivity

KW - Dielectric relaxation

KW - Nematic liquid crystal

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