37,083 research outputs found
Inverted critical adsorption of polyelectrolytes in confinement
What are the fundamental laws for the adsorption of charged polymers onto
oppositely charged surfaces, for convex, planar, and concave geometries? This
question is at the heart of surface coating applications, various complex
formation phenomena, as well as in the context of cellular and viral
biophysics. It has been a long-standing challenge in theoretical polymer
physics; for realistic systems the quantitative understanding is however often
achievable only by computer simulations. In this study, we present the findings
of such extensive Monte-Carlo in silico experiments for polymer-surface
adsorption in confined domains. We study the inverted critical adsorption of
finite-length polyelectrolytes in three fundamental geometries: planar slit,
cylindrical pore, and spherical cavity. The scaling relations extracted from
simulations for the critical surface charge density -defining the
adsorption-desorption transition-are in excellent agreement with our analytical
calculations based on the ground-state analysis of the Edwards equation. In
particular, we confirm the magnitude and scaling of for the concave
interfaces versus the Debye screening length and the extent of
confinement for these three interfaces for small values. For
large the critical adsorption condition approaches the planar limit.
The transition between the two regimes takes place when the radius of surface
curvature or half of the slit thickness is of the order of . We
also rationalize how gets modified for semi-flexible versus
flexible chains under external confinement. We examine the implications of the
chain length onto critical adsorption-the effect often hard to tackle
theoretically-putting an emphasis on polymers inside attractive spherical
cavities.Comment: 12 pages, 10 figures, RevTe
Non-linear Poisson-Boltzmann Theory for Swollen Clays
The non-linear Poisson-Boltzmann equation for a circular, uniformly charged
platelet, confined together with co- and counter-ions to a cylindrical cell, is
solved semi-analytically by transforming it into an integral equation and
solving the latter iteratively. This method proves efficient, robust, and can
be readily generalized to other problems based on cell models, treated within
non-linear Poisson-like theory. The solution to the PB equation is computed
over a wide range of physical conditions, and the resulting osmotic equation of
state is shown to be in fair agreement with recent experimental data for
Laponite clay suspensions, in the concentrated gel phase.Comment: 13 pages, 4 postscript figure
Structure of trajectories of complex matrix eigenvalues in the Hermitian-non-Hermitian transition
The statistical properties of trajectories of eigenvalues of Gaussian complex
matrices whose Hermitian condition is progressively broken are investigated. It
is shown how the ordering on the real axis of the real eigenvalues is reflected
in the structure of the trajectories and also in the final distribution of the
eigenvalues in the complex plane.Comment: 12 pages, 3 figure
Critical adsorption of polyelectrolytes onto charged Janus nanospheres
Based on extensive Monte Carlo simulations and analytical considerations we
study the electrostatically driven adsorption of flexible polyelectrolyte
chains onto charged Janus nanospheres. These net-neutral colloids are composed
of two equally but oppositely charged hemispheres. The critical binding
conditions for polyelectrolyte chains are analysed as function of the radius of
the Janus particle and its surface charge density, as well as the salt
concentration in the ambient solution. Specifically for the adsorption of
finite-length polyelectrolyte chains onto Janus nanoparticles, we demonstrate
that the critical adsorption conditions drastically differ when the size of the
Janus particle or the screening length of the electrolyte are varied. We
compare the scaling laws obtained for the adsorption-desorption threshold to
the known results for uniformly charged spherical particles, observing
significant disparities. We also contrast the changes to the polyelectrolyte
chain conformations and the binding energy distributions close to the
adsorption-desorption transition for Janus nanoparticles to those for simple
spherical particles. Finally, we discuss experimentally relevant
physico-chemical systems for which our simulations results may become
important. In particular, we observe similar trends with polyelectrolyte
complexation with oppositely but heterogeneously charged proteins.Comment: 13 pages, 11 figures, RevTeX
The Role of Fermions in Bubble Nucleation
We present a study of the role of fermions in the decay of metastable states
of a scalar field via bubble nucleation. We analyze both one and
three-dimensional systems by using a gradient expansion for the calculation of
the fermionic determinant. The results of the one-dimensional case are compared
to the exact results of previous work.Comment: 15 pages, revtex, 9 figure
Power-law statistics and stellar rotational velocities in the Pleiades
In this paper we will show that, the non-gaussian statistics framework based
on the Kaniadakis statistics is more appropriate to fit the observed
distributions of projected rotational velocity measurements of stars in the
Pleiades open cluster. To this end, we compare the results from the
and -distributions with the Maxwellian.Comment: 13 pages, 3 figure
- …