1,313 research outputs found
Charge Transport in Polymer Ion Conductors: a Monte Carlo Study
Diffusion of ions through a fluctuating polymeric host is studied both by
Monte Carlo simulation of the complete system dynamics and by dynamic bond
percolation (DBP) theory. Comparison of both methods suggests a multiscale-like
approach for calculating the diffusion coefficients of the ion
Dynamic percolation theory for particle diffusion in a polymer network
Tracer-diffusion of small molecules through dense systems of chain polymers
is studied within an athermal lattice model, where hard core interactions are
taken into account by means of the site exclusion principle. An approximate
mapping of this problem onto dynamic percolation theory is proposed. This
method is shown to yield quantitative results for the tracer correlation factor
of the molecules as a function of density and chain length provided the
non-Poisson character of temporal renewals in the disorder configurations is
properly taken into account
Capture numbers and islands size distributions in models of submonolayer surface growth
The capture numbers entering the rate equations (RE) for submonolayer film
growth are determined from extensive kinetic Monte Carlo (KMC) simulations for
simple representative growth models yielding point, compact, and fractal island
morphologies. The full dependence of the capture numbers on island size, and on
both the coverage and the D/F ratio between the adatom diffusion coefficient D
and deposition rate F is determined. Based on this information, the RE are
solved to give the RE island size distribution (RE-ISD). The RE-ISDs are shown
to agree well with the corresponding KMC-ISDs for all island morphologies. For
compact morphologies, however, this agreement is only present for coverages
smaller than about 5% due to a significantly increased coalescence rate
compared to fractal morphologies. As found earlier, the scaled KMC-ISDs as a
function of scaled island size approach, for fixed coverage, a limiting curve
for D/F going to infinity. Our findings provide evidence that the limiting
curve is independent of the coverage for point islands, while the results for
compact and fractal island morphologies indicate a dependence on the coverage.Comment: 13 pages, 12 figure
Melt viscosities of lattice polymers using a Kramers potential treatment
Kramers relaxation times and relaxation times and
for the end-to-end distances and for center of mass diffusion are
calculated for dense systems of athermal lattice chains. is defined
from the response of the radius of gyration to a Kramers potential which
approximately describes the effect of a stationary shear flow. It is shown that
within an intermediate range of chain lengths N the relaxation times
and exhibit the same scaling with N, suggesting that N-dependent
melt-viscosities for non-entangled chains can be obtained from the Kramers
equilibrium concept.Comment: submitted to: Journal of Chemical Physic
Loss of control in pattern-directed nucleation: a theoretical study
The properties of template-directed nucleation are studied close to the
transition where full nucleation control is lost and additional nucleation
occurs beyond the pre-patterned regions. First, kinetic Monte Carlo simulations
are performed to obtain information on a microscopic level. Here the
experimentally relevant cases of 1D stripe patterns and 2D square lattice
symmetry are considered. The nucleation properties in the transition region
depend in a complex way on the parameters of the system, i.e. the flux, the
surface diffusion constant, the geometric properties of the pattern and the
desorption rate. Second, the properties of the stationary concentration field
in the fully controlled case are studied to derive the remaining nucleation
probability and thus to characterize the loss of nucleation control. Using the
analytically accessible solution of a model system with purely radial symmetry,
some of the observed properties can be rationalized. A detailed comparison to
the Monte Carlo data is included
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