382 research outputs found
Electrostatic image effects for counter-ions between charged planar walls
We study the effect of dielectric inhomogeneities on the interaction between
two planparallel charged surfaces with oppositely charged mobile charges in
between. The dielectric constant between the surfaces is assumed to be
different from the dielectric constant of the two semiinfinite regions bounded
by the surfaces, giving rise to electrostatic image interactions. We show that
on the weak coupling level the image charge effects are generally small, making
their mark only in the second order fluctuation term. However, in the strong
coupling limit, the image effects are large and fundamental. They modify the
interactions between the two surfaces in an essential way. Our calculations are
particularly useful in the regime of parameters where computer simulations
would be difficult and extremely time consuming due to the complicated nature
of the long range image potentials.Comment: 21 pages, 8 figure
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
Positional, Reorientational and Bond Orientational Order in DNA Mesophases
We investigate the orientational order of transverse polarization vectors of
long, stiff polymer molecules and their coupling to bond orientational and
positional order in high density mesophases. Homogeneous ordering of transverse
polarization vector promotes distortions in the hexatic phase, whereas
inhomogeneous ordering precipitates crystalization of the 2D sections with
different orientations of the transverse polarization vector on each molecule
in the unit cell. We propose possible scenarios for going from the hexatic
phase, through the distorted hexatic phase to the crystalline phase with an
orthorhombic unit cell observed experimentally for the case of DNA.Comment: 4 pages, 2 figure
Van der Waals interactions across stratified media
Working at the Lifshitz level, we investigate the van der Waals interactions
across a series of layers with a periodic motif. We derive the complete form of
the van der Waals interaction as an explicit function of the number of periodic
layers. We then compare our result with an approximation based on an
anisotropic-continuum representation of the stratified medium. Satisfactory
agreement between discrete-layer and continuum models is reached only for
thicknesses of ten or more layers.Comment: 9 pages and 4 figure
Counterion-mediated Electrostatic Interactions between Helical Molecules
We study the interaction of two cylinders with helical charge distribution
mediated by neutralizing counterions, by analyzing the separation as well as
the azimuthal angle dependence of the interaction force in the weak and strong
coupling limit. While the azimuthal dependence of the interaction in the weak
coupling limit is overall small and mostly negligible, the strong coupling
limit leads to qualitatively new features of the interaction, among others also
to an orientationally dependent optimal configuration that is driven by angular
dependence of the correlation attraction. We investigate the properties of this
azimuthal ordering in detail and compare it to existing results.Comment: 11 pages, 12 figure
Exotic Electrostatics: Unusual Features of Electrostatic Interactions between Macroions
We present an overview of our understanding of electrostatic interactions
between charged macromolecular surfaces mediated by mobile counter- and coions.
The dichotomy between the weak and the strong coupling regimes is described in
detail and the way they engender repulsive and attractive interactions between
nominally equally charged macroions. We also introduce the concept of dressed
counterions in the case of many-component Coulomb fluids that are partially
weakly and partially strongly coupled to local electrostatic fields leading to
non-monotonic interactions between equally charged macroions. The effect of
quenched surface charge disorder on the counterion-mediated electrostatic
interactions is analyzed within the same conceptual framework and shown to lead
to unexpected and extraordinary electrostatic interactions between randomly
charged surfaces with equal mean surface charge densities or even between
effectively neutral macroion surfaces. As a result, these recent developments
challenge some cherished notions of pop culture.Comment: 18 pages, 5 figure
Coupling between Smectic and Twist Modes in Polymer Intercalated Smectics
We analyse the elastic energy of an intercalated smectic where
orientationally ordered polymers with an average orientation varying from layer
to layer are intercalated between smectic planes. The lowest order terms in the
coupling between polymer director and smectic layer curvature are added to the
smectic elastic energy. Integration over the smectic degrees of freedom leaves
an effective polymer twist energy that has to be included into the total
polymer elastic energy leading to a fluctuational renormalization of the
intercalated polymer twist modulus. If the polymers are chiral this in its turn
leads to a renormalization of the cholesteric pitch.Comment: 8 pages, 1 fig in ps available from [email protected] Replaced
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