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Article
Proton Nuclear Magnetic relaxation study of molecular dynamics in the
Ferroelectric Liquid Crystal Val.DOC
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João L Figueirinhas
o
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A. Ferraz
o
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A. C. Ribeiro
o
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H. T. Nguyen
o
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F. Noack
o
Ferroelectrics (Impact Factor: 0.47). 09/1993; 146(1):123-135. DOI: 10.1080/00150199308008533
ABSTRACT
Molecular dynamics studies were carried out in the SA and SC mesophases of the Ferroelectric Liquid Crystal
Val.DOC by means of longitudinal proton spin relaxation dispersion. Fast field-cycling and conventional Nuclear
Magnetic Resonance (NMR) techniques were used to obtain the frequency dependence of T1 covering frequencies
from 10 to 3 × 10 Hz at two different temperatures in each mesophase. The T dispersion in both mesophases could
be well modeled by the proposed dominant relaxation mechanisms, namely collective motions, molecular self
diffusion and local molecular rotations. A Soft mode contribution to the spin-lattice relaxation could not be singled out
from the contribution of other collective motions. The diffusion constant D⊥perpendicular to the director was obtained
at all temperatures studied and involves an activation energy of about 35 kJ/mol. Effective correlation times
characterizing the average molecular rotations around the long axis and fluctuations of this axis, respectively, were
evaluated; their temperature dependence agrees with an Arrhenius type law with activation energies of about 50
kJ/mol.
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Article: Molecular order in bilayer, anticlinic and ferroelectric smectic C mesophases
A. Carvalho · P.J. Sebastião · A. Ferraz · A.C. Ribeiro · H.T. Nguyen
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ABSTRACT: In this work we present a proton NMR comparative study of the molecular order in the smectic C2 (),
smectic C^* () and anticlinic smectic C phases ( and ) of two liquid crystalline compounds. The second moments of
the experimental proton NMR spectra are well explained taking into account two different molecular orientations
models. From the analysis of our experimental results it was possible to estimate the tilt angles for all the smectic C
phases studied in this work.
No preview · Article · Jul 2000 · The European Physical Journal E
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Article: Contribution of Proton NMR Relaxation to the Investigation of Molecular Dynamics and Molecular
Organisation in Liquid Crystalline Phases
AC Ribeiro · P. J. Sebastião · C. Cruz
[Show abstract] [Hide abstract]
ABSTRACT: We present in this paper some general remarks concerning proton Nuclear Magnetic Resonance
studies carried out in particular phases of calamitic, polycatenar and discotic molecules and we show how these
studies can be used to understand the molecular dynamics in different types of mesophases. We also illustrate how
these studies can contribute, in some cases, to test the validity of molecular organisation models proposed in the
literature to describe particular structures detected by X-ray diffraction.
No preview · Article · Jun 2001 · Molecular Crystals and Liquid Crystals
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