38 research outputs found
Correlated and Decorrelated Positional and Orientational Order in the Nucleosomal Core Particle Mesophases
We investigate the orientational order of transverse polarization vectors of
long columns of nucleosomal core particles and their coupling to positional
order in high density mesophases discovered recently. Inhomogeneous polar
ordering of these columns precipitates crystalization of the 2D sections with
different orientations of the transverse polarization vector on each column in
the unit cell. We propose possible scenarios for going from the 2D hexagonal
phase into distorted lamellar and related phases observed experimentally.Comment: 4 pages and 2 figure
Re-entrant ferroelectricity in liquid crystals
The ferroelectric (Sm C) -- antiferroelectric (Sm C) -- reentrant
ferroelectric (re Sm C) phase temperature sequence was observed for system
with competing synclinic - anticlinic interactions. The basic properties of
this system are as follows (1) the Sm C phase is metastable in temperature
range of the Sm C stability (2) the double inversions of the helix
handedness at Sm C -- Sm C and Sm C% -- re-Sm C phase
transitions were found (3) the threshold electric field that is necessary to
induce synclinic ordering in the Sm C phase decreases near both Sm
C -- Sm C and Sm C -- re-Sm C phase boundaries, and it has
maximum in the middle of the Sm C stability region. All these properties
are properly described by simple Landau model that accounts for nearest
neighboring layer steric interactions and quadrupolar ordering only.Comment: 10 pages, 5 figures, submitted to PR
Flexoelectricity and piezoelectricity - reason for rich variety of phases in antiferroelectric liquid crystals
The free energy of antiferroelectric liquid crystal which takes into account
polar order explicitly is presented. Steric, van der Waals, piezoelectric and
flexoelectric interactions to the nearest layers and dipolar electrostatic
interactions to the nearest and to the next nearest layers induce indirect tilt
interactions with chiral and achiral properties, which extend to the third and
to the fourth nearest layers. Chiral indirect interactions between tilts can be
large and induce helicoidal modulations even in systems with negligible chiral
van der Waals interactions. If indirect chiral interactions compete with chiral
van der Waals interactions, the helix unwinding is possible. Although strength
of microscopic interactions change monotonically with decreasing temperature,
effective interlayer interactions change nonmonotonically and give rise to
nonmonotouous change of modulation period through various phases. Increased
enatiomeric excess i.e. increased chirality changes the phase sequence.Comment: 4 pages, 1 figur
Parameterization invariance and shape equations of elastic axisymmetric vesicles
The issue of different parameterizations of the axisymmetric vesicle shape
addressed by Hu Jian-Guo and Ou-Yang Zhong-Can [ Phys.Rev. E {\bf 47} (1993)
461 ] is reassesed, especially as it transpires through the corresponding Euler
- Lagrange equations of the associated elastic energy functional. It is argued
that for regular, smooth contours of vesicles with spherical topology,
different parameterizations of the surface are equivalent and that the
corresponding Euler - Lagrange equations are in essence the same. If, however,
one allows for discontinuous (higher) derivatives of the contour line at the
pole, the differently parameterized Euler - Lagrange equations cease to be
equivalent and describe different physical problems. It nevertheless appears to
be true that the elastic energy corresponding to smooth contours remains a
global minimum.Comment: 10 pages, latex, one figure include
The prolate-to-oblate shape transition of phospholipid vesicles in response to frequency variation of an AC electric field can be explained by the dielectric anisotropy of a phospholipid bilayer
The external electric field deforms flaccid phospholipid vesicles into
spheroidal bodies, with the rotational axis aligned with its direction.
Deformation is frequency dependent: in the low frequency range (~ 1 kHz), the
deformation is typically prolate, while increasing the frequency to the 10 kHz
range changes the deformation to oblate. We attempt to explain this behaviour
with a theoretical model, based on the minimization of the total free energy of
the vesicle. The energy terms taken into account include the membrane bending
energy and the energy of the electric field. The latter is calculated from the
electric field via the Maxwell stress tensor, where the membrane is modelled as
anisotropic lossy dielectric. Vesicle deformation in response to varying
frequency is calculated numerically. Using a series expansion, we also derive a
simplified expression for the deformation, which retains the frequency
dependence of the exact expression and may provide a better substitute for the
series expansion used by Winterhalter and Helfrich, which was found to be valid
only in the limit of low frequencies. The model with the anisotropic membrane
permittivity imposes two constraints on the values of material constants:
tangential component of dielectric permittivity tensor of the phospholipid
membrane must exceed its radial component by approximately a factor of 3; and
the membrane conductivity has to be relatively high, approximately one tenth of
the conductivity of the external aqueous medium.Comment: 17 pages, 6 figures; accepted for publication in J. Phys.: Condens.
Matte