Search results for "Method"

Orientational ordering transitions of semiflexible polymers in thin films: A Monte Carlo simulation

2011

Athermal solutions (from dilute to concentrated) of semiflexible macromolecules confined in a film of thickness D between two hard walls are studied by means of grand-canonical lattice Monte Carlo simulation using the bond fluctuation model. This system exhibits two phase transitions as a function of the thickness of the film and polymer volume fraction. One of them is the bulk isotropic-nematic first-order transition, which ends in a critical point on decreasing the film thickness. The chemical potential at this transition decreases with decreasing film thickness ("capillary nematization"). The other transition is a continuous (or very weakly first-order) transition in the layers adjacent …

1995

Surfaces have a profound effect on the structure and related properties of multiphase polymeric materials, such as polymer mixtures and block copolymer mesophases. In particular, phase transitions in the bulk (unmixing, microphase separation, etc.) may be complemented by surface-induced transitions (formation of wetting layers, surface-directed spinodal decomposition, surface-induced ordering). This review gives a brief introduction to the phenomenological theories of such phenomena, emphasizing the simplest approach based on Flory—Huggins—de Gennes free energy functionals and associated Monte Carlo simulations. More sophisticated theories and recent experiments are mentioned briefly.

One- and two-component bottle-brush polymers: simulations compared to theoretical predictions

2007

Scaling predictions and results from self-consistent field calculations for bottle-brush polymers with a rigid backbone and flexible side chains under good solvent conditions are summarized and their validity and applicability is assessed by a comparison with Monte Carlo simulations of a simple lattice model. It is shown that under typical conditions, as they are also present in experiments, only a rather weak stretching of the side chains is realized, and then the scaling predictions based on the extension of the Daoud-Cotton blob picture are not applicable. Also two-component bottle brush polymers are considered, where two types (A,B) of side chains are grafted, assuming that monomers of …

Photocatalytic ozonation: Maximization of the reaction rate and control of undesired by-products

2015

Abstract In the so-called photocatalytic ozonation (PO) synergistic effects between photocatalysis and ozonation enhance the rate of oxidation of organic compounds, therefore this integrated process is very promising for use in water treatment. In the present work, it is demonstrated that the improvement that can be obtained by the integrated process in comparison with the uncoupled processes depends on the relative weight between photocatalysis and ozonation. In this respect, it has been found that a relatively low rate of photocatalysis (0.3 times the rate of ozonation) is sufficient to get the highest synergy and to maximize the performances in the oxidation of formate, the adopted model…

The intermediate coherent scattering function of entangled polymer melts: a Monte Carlo test of des Cloizeaux' theory

1994

Using the bond fluctuation model for flexible polymer chains in a dense melt the intermediate coherent scattering function for chains containing N=200 monomers is calculated and interpreted in terms of a recent theory of des Cloizeaux. The theory yields an explicit description for the crossover from the Rouse model to the regime where reptation prevails, for the limit N→∞. While the Monte Carlo data are qualitatively compatible with this description, an accurate estimation of the tube diameter is prevented due to the onset of a diffusive decay of the scattering function, not included in the theory. For a full quantitative analysis of the Monte Carlo data (as well as of experiments on chains…

Third virial coefficient for 4-arm and 6-arm star polymers

2008

We discuss the computation of the third virial coefficient in polymer systems, focusing on an additional contribution absent in the case of monoatomic fluids. We determine the interpenetration ratio and several quantities that involve the third virial coefficient for star polymers with 4 and 6 arms in the good-solvent regime, in the limit of a large degree of polymerization.

Phase transitions in a single polymer chain: A micro-canonical analysis of Wang–Landau simulations

2008

Abstract We present simulation results for the phase behavior of a single chain for a flexible lattice polymer model using the Wang–Landau sampling idea. Using the micro-canonical density of states obtained with this method we will discuss the ability of an analysis in the micro-canonical ensemble to locate the coil-globule (continuous) and liquid–solid (first-order) transitions found for this problem using a canonical analysis.

A Monte Carlo Study of Living Polymers in 2D: Effect of Small Chains on Static Properties

1996

A slithering snake algorithm is combined with a binding and breaking chain algorithm to simulate the static behavior of living polymers according to Cates' description. It is shown that this simple two-dimensional simulation on a square lattice gives good agreement with the mean field theory. However, the large amount of small contour length chains for small values of the mean average length 〈L 〉 appears to be one of the reasons for the discrepancies observed between the simulated results and the mean field theory. This finding could explain disagreements between experimental observation and theory. Also, the results are not in favor of a swelling of the greater chains by the smaller one.

KINETICS OF POLYMER EJECTION FROM CAPSID CONFINEMENT: SCALING CONSIDERATIONS AND COMPUTER EXPERIMENT

2012

We investigate the ejection dynamics of a flexible polymer chain out of confined environment by means of scaling considerations and Monte Carlo simulations. Situations of this kind arise in different physical contexts, including a flexible synthetic polymer partially confined in a nanopore and a viral genome partially ejected from its capsid. In the case of cylindric confinement the entropic driving force which pulls the chain out of the pore is argued to be constant once a few persistent lengths are out of the pore. We demonstrate that in this case the ejection dynamics follows a [Formula: see text]-law with elapsed time t. The mean ejection time τ depends nonmonotonically on chain length…

Pulling Single Adsorbed Bottle-Brush Polymers off a Flat Surface: A Monte Carlo Simulation

2013

Force versus extension behavior of flexible chains and semiflexible bottle-brush polymers adsorbed from a good solvent on a planar substrate is studied by Monte Carlo simulation of the bond fluctua...