6,226 research outputs found
A variational approach to necklaces formation in polyelectrolytes
By means of a variational approach we study the conditions under which a
polyelectrolyte in a bad solvent will undergo a transition from a rod-like
structure to a ``necklace'' structure in which the chain collapses into a
series of globules joined by stretched chain segments.Comment: 6 pages, 4 figures (unfortunately big). Requires revtex, eps
Collapse of Flexible Polyelectrolytes in Multivalent Salt Solutions
The collapse of flexible polyelectrolytes in a solution of multivalent
counterions is studied by means of a two state model. The states correspond to
rod-like and spherically collapsed conformations respectively. We focus on the
very dilute monomer concentration regime where the collapse transition is found
to occur when the charge of the multivalent salt is comparable (but smaller) to
that of the monomers. The main contribution to the free energy of the collapsed
conformation is linear in the number of monomers , since the internal state
of the collapsed polymer approaches that of an amorphous ionic solid. The free
energy of the rod-like state grows as , due to the electrostatic energy
associated with that shape. We show that practically all multivalent
counterions added to the system are condensed into the polymer chain, even
before the collapse.Comment: LaTeX-revtex, psfig file, 4 figure
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
- …