6,367 research outputs found
Surface-induced layer formation in polyelectrolytes
We analyze, by means of an RPA calculation, the conditions under which a
mixture of oppositely charged polyelectrolytes can micro-segregate in the
neighborhood of a charged surface creating a layered structure. A number of
stable layers can be formed if the surface is sufficiently strongly charged
even at temperatures at which the bulk of the mixture is homogeneous.Comment: 6 pages, 3 figures, revtex, epsf, psfi
Competing Interactions among Supramolecular Structures on Surfaces
A simple model was constructed to describe the polar ordering of
non-centrosymmetric supramolecular aggregates formed by self assembling
triblock rodcoil polymers. The aggregates are modeled as dipoles in a lattice
with an Ising-like penalty associated with reversing the orientation of nearest
neighbor dipoles. The choice of the potentials is based on experimental results
and structural features of the supramolecular objects. For films of finite
thickness, we find a periodic structure along an arbitrary direction
perpendicular to the substrate normal, where the repeat unit is composed of two
equal width domains with dipole up and dipole down configuration. When a short
range interaction between the surface and the dipoles is included the balance
between the up and down dipole domains is broken. Our results suggest that due
to surface effects, films of finite thickness have a none zero macroscopic
polarization, and that the polarization per unit volume appears to be a
function of film thickness.Comment: 3 pages, 3 eps figure
Synchronization of the Frenet-Serret linear system with a chaotic nonlinear system by feedback of states
A synchronization procedure of the generalized type in the sense of Rulkov et
al [Phys. Rev. E 51, 980 (1995)] is used to impose a nonlinear Malasoma chaotic
motion on the Frenet-Serret system of vectors in the differential geometry of
space curves. This could have applications to the mesoscopic motion of
biological filamentsComment: 12 pages, 7 figures, accepted at Int. J. Theor. Phy
Charge reversal of colloidal particles
A theory is presented for the effective charge of colloidal particles in
suspensions containing multivalent counterions. It is shown that if colloids
are sufficiently strongly charged, the number of condensed multivalent
counterion can exceed the bare colloidal charge leading to charge reversal.
Charge renormalization in suspensions with multivalent counterions depends on a
subtle interplay between the solvation energies of the multivalent counterions
in the bulk and near the colloidal surface. We find that the effective charge
is {\it not} a monotonically decreasing function of the multivalent salt
concentration. Furthermore, contrary to the previous theories, it is found that
except at very low concentrations, monovalent salt hinders the charge reversal.
This conclusion is in agreement with the recent experiments and simulations
Polyelectrolyte Multilayering on a Charged Planar Surface
The adsorption of highly \textit{oppositely} charged flexible
polyelectrolytes (PEs) on a charged planar substrate is investigated by means
of Monte Carlo (MC) simulations. We study in detail the equilibrium structure
of the first few PE layers. The influence of the chain length and of a (extra)
non-electrostatic short range attraction between the polycations and the
negatively charged substrate is considered. We show that the stability as well
as the microstructure of the PE layers are especially sensitive to the strength
of this latter interaction. Qualitative agreement is reached with some recent
experiments.Comment: 28 pages; 11 (main) Figs - Revtex4 - Higher resolution Figs can be
obtained upon request. To appear in Macromolecule
Stability of additive-free water-in-oil emulsions
We calculate ion distributions near a planar oil-water interface within
non-linear Poisson-Boltzmann theory, taking into account the Born self-energy
of the ions in the two media. For unequal self-energies of cations and anions,
a spontaneous charge separation is found such that the water and oil phase
become oppositely charged, in slabs with a typical thickness of the Debye
screening length in the two media. From the analytical solutions, the
corresponding interfacial charge density and the contribution to the
interfacial tension is derived, together with an estimate for the
Yukawa-potential between two spherical water droplets in oil. The parameter
regime is explored where the plasma coupling parameter exceeds the
crystallization threshold, i.e. where the droplets are expected to form
crystalline structures due to a strong Yukawa repulsion, as recently observed
experimentally. Extensions of the theory that we discuss briefly include
numerical calculations on spherical water droplets in oil, and analytical
calculations of the linear PB-equation for a finite oil-water interfacial
width.Comment: 9 pages, 4 figures, accepted by JPCM for proceedings of LMC
The mean-field theory for attraction between like-charged macromolecules
A mean-field theory based on Gibbs-Bogoliubov inequality is constructed to
study the interactions between two like-charged polyions. It is shown that
contrary to the previously established paradigm, a properly constructed
mean-field theory can quantitatively account for the attractive interactions
between two like-charged rods.Comment: 5 pages, 2 figures, elsart.sty neede
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