Journal ArticleDOI
Nematic-Isotropic Transition: Thermal Hysteresis and Magnetic Field Effects
T Riste,L Dobrzynski +1 more
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Using neutron scattering, the effect of an applied magnetic field on the nematic-isotropic transition temperature in para-azoxy-anisole (PAA) is studied and data indicate that in zero field the transition may be of second order.Abstract:
Using neutron scattering, we have studied the effect of an applied magnetic field on the nematic-isotropic transition temperature ${T}_{c}$ in para-azoxy-anisole (PAA). We have, for the first time, been able to measure a thermal hysteresis width, $({T}_{+}^{*}{\ensuremath{-}T}_{\ensuremath{-}}^{*}){/T}_{c}$, and find a value $3.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ for a field-aligned sample, much lower than any previous estimate, and decreasing to zero for weaker fields. Also ${T}_{c}$ decreases with the field, as does the step ${Q}_{c}$ in the order parameter. The data at the lowest fields indicate that in zero field the transition may be of second order, and we correlate this with an observed increase of the director fluctuations.read more
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References
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Journal ArticleDOI
The characterization of order in nematic liquid crystals
R. Alben,J.R. McColl,C. S. Shih +2 more
TL;DR: In this paper, it was pointed out that the usual one-parameter approximation for the order parameter tensor in nematic liquid crystals is not always adequate, and that a twoparameter description is indicated by experiments, and it was shown that for p-azoxyanisole at 120°C, the two parameters have the values; S ¯ = 0.52, D ¯ =0.07, where S ¯ is the usual nematic order parameter and D ¯ describes the difference in the tendency of the two transverse molecular axes to be oriented along the average
Journal ArticleDOI
Investigation of nematic order by coherent neutron scattering
TL;DR: The mathematical relationship between the orientational order parameters and the coherent neutron scattering cross section for a nematic liquid crystal is given in this article, where the single-molecule part of the cross section is evaluated within the meanfield approximation and combined with experimental results to give information about molecular orientational ordering in terms of P2, P4, and P6.
Journal ArticleDOI
Nematic-isotropic phase transition: An extended mean field theory.
TL;DR: This work shows that not only does the presence of density change at the N-I transition argue for the necessary presence of the density-dependent, isotropic component of the intermolecular interaction in the nematic Hamiltonian, but the incorporation of that extra part also materially affects the character of the N -I transition.
Journal ArticleDOI
Nematic liquid crystals in high magnetic field: Quenching of the transverse fluctuations
B. Malraison,Y. Poggi,E. Guyon +2 more
TL;DR: In this paper, a detailed account of the IEB effect near a second-order smectic transition is connected quantitatively with the divergence of the bend elastic constant, where the increase of IEB is connected with the decrease of the elastic constants.
Journal ArticleDOI
Fractional Brownian motion of director fluctuations in nematic ordering.
TL;DR: Temporal director fluctuations in nematic ordering were studied by computer simulation on the Lebwohl-Lasher model as well as by neutron-scattering experiments on the nematogen d-PAA, finding a value of H≃1 for the nematic phase, characterizing fractional Brownian motion.