154 research outputs found
The Crumpling Transition of Dynamically Triangulated Random Surfaces
We present the crumpling transition in three-dimensional Euclidian space of
dynamically triangulated random surfaces with edge extrinsic curvature and
fixed topology of a sphere as well as simulations of a dynamically triangulated
torus. We used longer runs than previous simulations and give new and more
accurate estimates of critical exponents. Our data indicate a cusp singularity
in the specific heat. The transition temperature, as well as the exponents are
topology dependent.Comment: 11pages (PostScript figures are not included. Request author
directly.), LaTeX, TPHD-93020
Structural Properties of Two-Dimensional Polymers
We present structural properties of two-dimensional polymers as far as they
can be described by percolation theory. The percolation threshold, critical
exponents and fractal dimensions of clusters are determined by computer
simulation and compared to the results of percolation theory. We also describe
the dependence of the typical cluster structures on the reaction rate.Comment: 7 pages, LaTeX with RevTeX and epsf styles and PostScript figures
included (uuencoded shell archive), TVP-93051
Deformation of polymer films by bending forces
We study the deformation of nano--scale polymer films which are subject to
external bending forces by means of computer simulation. The polymer is
represented by a generalized bead--spring--model, intended to reproduce
characteristic features of n--alkanes. The film is loaded by the action of a
prismatic blade which is pressed into the polymer bulk from above and a pair of
columns which support the film from below. The interaction between blade and
support columns and the polymer is modelled by the repulsive part of a
Lennard-Jones potential. For different system sizes as well as for different
chainlengths, this nano--scale experiment is simulated by molecular dynamics
methods. Our results allow us to give a first characterization of deformed
states for such films. We resolve the kinetic and the dynamic stage of the
deformation process in time and access the length scale between discrete
particle and continuum mechanics behaviour. For the chainlengths considered
here, we find that the deformation process is dominated by shear. We observe
strangling effects for the film and deformation fluctuations in the steady
state.Comment: 15 pages, 8 figure
Reconstruction of the Free Energy in the Metastable Region using the Path Ensemble
By quenching into the metastable region of the three-dimensional Ising model,
we investigate the paths that the magnetization (energy) takes as a function of
time. We accumulate the magnetization (energy) paths into time-dependent
distributions from which we reconstruct the free energy as a function of the
magnetic field, temperature and system size. From the reconstructed free
energy, we obtain the free energy barrier that is associated with the
transition from a metastable state to the stable equilibrium state. Although
mean-field theory predicts a sharp transition between the metastable and the
unstable region where the free energy barrier is zero, the results for the
nearest-neighbour Ising model show that the free energy barrier does not go
zero
Structure of Polymer Brushes in Cylindrical Tubes: A Molecular Dynamics Simulation
Molecular Dynamics simulations of a coarse-grained bead-spring model of
flexible macromolecules tethered with one end to the surface of a cylindrical
pore are presented. Chain length and grafting density are varied
over a wide range and the crossover from ``mushroom'' to ``brush'' behavior is
studied for three pore diameters. The monomer density profile and the
distribution of the free chain ends are computed and compared to the
corresponding model of polymer brushes at flat substrates. It is found that
there exists a regime of and for large enough pore diameter where
the brush height in the pore exceeds the brush height on the flat substrate,
while for large enough and (and small enough pore diameters) the
opposite behavior occurs, i.e. the brush is compressed by confinement. These
findings are used to discuss the corresponding theories on polymer brushes at
concave substrates.Comment: 11 figure
Monte Carlo simulations reveal the straightening up of an end-grafted flexible chain with a rigid side chain
We have studied the conformational properties of a flexible end-grafted chain
(length ) with a rigid side chain (length ) by means of Monte Carlo
simulations. Depending on the lengths and and the branching site, ,
we observe a considerable straightening of the flexible backbone as quantified
via the gyration tensor. For , i.e. when attaching the side chain to the
free end of the flexible backbone, the effect was strongest
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