592 research outputs found
Adsorption of Externally Stretched Two-Dimensional Flexible and Semi-flexible Polymers near an Attractive Wall
We study analytically a model of a two dimensional, partially directed,
flexible or semiflexible polymer, attached to an attractive wall which is
perpendicular to the preferred direction. In addition, the polymer is stretched
by an externally applied force. We find that the wall has a dramatic effect on
the polymer. For wall attraction smaller than the non-sequential nearest
neighbor attraction, the fraction of monomers at the wall is zero and the model
is the same as that of a polymer without a wall. However, for greater than, the
fraction of monomers at the wall undergoes a first order transition from unity
at low temperature and small force, to zero at higher temperatures and forces.
We present phase diagram for this transition. Our results are confirmed by
Monte-Carlo simulations.Comment: 15 pages, 6 figure
Hard colloidal rods near a soft wall: wetting, drying, and symmetry breaking
Within an Onsager-like density functional theory we explore the thermodynamic
and structural properties of an isotropic and nematic fluid of hard needle-like
colloids in contact with a hard substrate coated with a soft short-ranged
attractive or repulsive layer. As a function of the range and the strength of
the soft interactions we find wetting and drying transitions, a pre-drying
line, and a symmetry-breaking transition from uniaxial to biaxial in the
wetting and drying film.Comment: 7 pages, 2 figure
Monte-Carlo simulation of string-like colloidal assembly
We study structural phase transition of polymer-grafted colloidal particles
by Monte Carlo simulations on hard spherical particles. The interaction
potential, which has a weak repulsive step outside the hard core, was validated
with use of the self-consistent field calculations. With this potential,
canonical Monte Carlo simulations have been carried out in two and three
dimensions using the Metropolis algorithm. At low temperature and high density,
we find that the particles start to self-assemble and finally align in strings.
By analyzing the cluster size distribution and string length distribution, we
construct a phase diagram and find that this string-like assembly is related to
the percolation phenomena. The average string length diverges in the region
where the melting transition line and the percolation transition line cross,
which is similar to Ising spin systems where the percolation transition line
and the order-disorder line meet on the critical point.Comment: 7 pages, 6 figures, Accepted for Europhysics Letter
Effect of Adsorbing and Nonadsorbing Polymer on the Interaction Between Colloidal Particles
In this paper it is described how a recent theoretical model can be applied to a system of two colloidal particles in the presence of adsorbing and nonadsorbing polymer. It turns out that in the case of adsorption the most suitable boundary condition is restricted equilibrium, in which a constant amount of polymer is in local equilibrium inside the gap between two particles. At a low polymer dose the formation of bridges gives rise to bridging flocculation, at higher amounts of polymer steric stabilization occurs due to the mutual repulsion of two extended polymer layers. If the polymer does not adsorb on the particles, full equilibrium applies in which the chemical potentials of solvent and polymer in the gap are the same as in the equilibrium bulk solution, The depletion of polymer near the surface may lead to depletion flocculation in not too concentrated polymer solutions. In very concentrated systems the thickness of the depletion zone is relatively small, and the attraction between the particles becomes too weak to overcome the particle entropy, Then the system is restabilized
Irreversibility and Polymer Adsorption
Physisorption or chemisorption from dilute polymer solutions often entails
irreversible polymer-surface bonding. We present a theory of the
non-equilibrium layers which result. While the density profile and loop
distribution are the same as for equilibrium layers, the final layer comprises
a tightly bound inner part plus an outer part whose chains make only fN surface
contacts where N is chain length. The contact fractions f follow a broad
distribution, P(f) ~ f^{-4/5}, in rather close agreement with strong
physisorption experiments [H. M. Schneider et al, Langmuir v.12, p.994 (1996)].Comment: 4 pages, submitted to Phys. Rev. Let
Single polymer adsorption in shear: flattening versus hydrodynamic lift and corrugation effects
The adsorption of a single polymer to a flat surface in shear is investigated
using Brownian hydrodynamics simulations and scaling arguments. Competing
effects are disentangled: in the absence of hydrodynamic interactions, shear
drag flattens the chain and thus enhances adsorption. Hydrodynamic lift on the
other hand gives rise to long-ranged repulsion from the surface which preempts
the surface-adsorbed state via a discontinuous desorption transition, in
agreement with theoretical arguments. Chain flattening is dominated by
hydrodynamic lift, so overall, shear flow weakens the adsorption of flexible
polymers. Surface friction due to small-wavelength surface potential
corrugations is argued to weaken the surface attraction as well.Comment: 6 pages, 4 figure
Adsorption transition of a self-avoiding polymer chain onto a rigid rod
The subject of this work is the adsorption transition of a long flexible
self-avoiding polymer chain onto a rigid thin rod. The rod is represented by a
cylinder of radius R with a short-ranged attractive surface potential for the
chain monomers. General scaling results are obtained by using renormalization
group arguments in conjunction with available results for quantum field
theories with curved boundaries [McAvity and Osborn 1993 Nucl. Phys. B 394,
728]. Relevant critical exponents are identified and estimated using geometric
arguments.Comment: 19 pages, 4 figures. To appear in: J. Phys.: Condens. Matter, special
issue dedicated to Lothar Schaefer on the occasion of his 60th birthda
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