Search results for "Monte Carlo method"

Momentum-dependent interfacial tension in polymer solutions

2002

A model for the interface between a concentrated and a very dilute polymer solution is studied by Monte Carlo simulations at temperatures below the Theta temperature (in bad solvent conditions). The wave-number–dependent interfacial tension γ(q) is extracted from an analysis of the capillary wave amplitudes. It is shown that γ(q) decreases monotonically with q2, while no evidence is found for the predicted increase γ(q) ∝ κq2 with a positive bending rigidity κ of the interface at large q. Consequences for the interpretations of simulations and experiments on interfacial widths are briefly discussed.

‘Intrinsic’ profiles and capillary waves at interfaces between coexisting phases in polymer blends

2001

Abstract Lateral fluctuations in the local position of the center of the interface between coexisting phases in unmixed polymer blends lead to a broadening of interfacial widths; comparing self-consistent field predictions for the ‘intrinsic’ profile to simulations (or experiments), this ‘capillary wave’ broadening needs consideration. This problem has been studied by extensive Monte Carlo simulations of the bond fluctuation model for symmetrical polymer mixtures, both for free interfaces (between bulk phases) and for confined interfaces (in thin films between parallel walls). While the capillary wave predictions at large length scales are confirmed, the extraction of the ‘intrinsic’ profil…

Interfaces between coexisting phases of polymer mixtures: Comparison between Monte Carlo simulations and theoretical predictions

1997

Large scale Monte Carlo investigations of the interface between A-rich and B-rich phases of symmetric binary (AB) polymer mixtures are presented, using the bond fluctuation model of flexible chains with NA=NB=N=32 effective monomers. The temperature range studied, 0.144<T/Tc0.759, includes both the strong and the weak segregation limit. Interfacial free energy and interfacial structure are studied, and compared to predictions based on the selfconsistent field theory. Also the broadening of the interfacial width due to capillary waves is considered, and finite size effects due to the confinement of interfaces in thin films of polymer blends are discussed.

Monte Carlo simulation of the glass transition in polymeric systems: Recent developments

1995

Abstract The bond fluctuation model on square and s.c. lattices is used as a coarse-grained model for flexible polymers in dense melts. Using an energy that favours long bonds, a conflict is created between the tendency of the bonds to stretch at low temperatures and packing constraints. This simple concept of ‘geometric frustration’ leads to glass transition. Both static and dynamic properties of this model are investigated by Monte Carlo simulations, paying attention to effects found by varying the cooling rate and the chain length N of the polymers. In two and three spatial dimensions an effective (cooling-rate dependent) glass transition temperature T g can be defined, where the system …

Adsorption-induced polymer translocation through a nanopore: a Monte Carlo investigation

2005

Abstract We study the translocation of a coarse-grained flexible polymer through a nanopore in a membrane induced by its adsorption on the trans side of the membrane. Dramatic differences in the threading behavior are observed if the adhesion to the membrane wall, e w , is below or above the adsorption threshold e c r . For e w e c r (weak adsorption) the activation barrier for translocation is at c cis 0 ≈ N / 2 (in terms of the fraction of chain c cis = N cis / N before the pore), independent of chain length N. For e w > e c r this barrier is at a constant (vanishing) number of passed trans monomers for all N. The mean time of chain passage τ trans ∝ c cis 1.3 when c cis c cis 0 . It scal…

Surface anchoring on liquid crystalline polymer brushes

2002

We present a Monte Carlo study of the surface anchoring of a nematic fluid on swollen layers of grafted liquid crystalline chain molecules. The liquid crystalline particles are modeled by soft repulsive ellipsoids, and the chains are made of the same particles. An appropriately modified version of the configurational bias Monte Carlo algorithm is introduced, which removes and redistributes chain bonds rather than whole monomers. With this algorithm, a wide range of grafting densities could be studied. The substrate is chosen such that it favors a planar orientation (parallel to the surface). Depending on the grafting density, we find three anchoring regimes: planar, tilted, and perpendicula…

Dynamics of confined polymer melts: Recent Monte Carlo simulation results

2000

The dynamic behavior of thin polymer films is studied by Monte Carlo simulations of a simplified lattice model. The film geometry is realized by two opposite hard walls whose distance is varied in the simulations. In the films the dynamics is accelerated with respect to the bulk, leading to a decrease of the extrapolated glass transition temperature with decreasing film thickness.

Polymer solutions confined in slit-like pores with attractive walls: An off-lattice Monte Carlo study of static properties and chain dynamics

1996

Using a bead spring model of flexible polymer chains, the density profiles and chain configurational properties of polymer solutions confined between parallel plates were studied. A wide range of density ϕ, chain length N, and strength e of a short-range attractive wall potential was investigated. Both a temperature T in the good solvent regime (T > θ, θ being the Theta temperature where a chain in unconfined bulk three-dimensional solution would behave ideally) and a temperature in the bad solvent regime (T θ) show a crossover from two-dimensional excluded volume behavior (Rg ∝ N2ν with ν = 3/4) to ideal random walk behavior (ν = 1/2), the relaxation times show effective exponents Zeff (τ …

1988

Monte Carlo simulations are presented for binary (AB) symmetric polymer mixtures (chain lengths NANBN) for the case that an attractive interaction ϵ exists between monomers of the same kind, and the limiting case that one species (B) is very diluted. It is shown that with increasing interaction strength ϵ/(kB · T), T being the absolute temperature, the minority chains collapse to a very dense configuration, while the majority chains stay nearly Gaussian. Both chain radii, structure factors and numbers of nearest neighbour contacts are discussed.

Polymer Films in the Normal-Liquid and Supercooled State: A Review of Recent Monte Carlo Simulation Results

2000

This paper reviews recent Monte Carlo simulation studies of the glassy behavior in thin polymer films. The simulations employ a version of the bond-fluctuation lattice model, in which the glass transition is driven by the competition between a stiffening of the polymers and their dense packing in the melt. The melt is geometrically confined between two impenetrable walls separated by distances ranging from once to about fifteen times the bulk radius of gyration. The confinement influences static and dynamic properties of the films: Chains close to the wall preferentially orient parallel to it. This orientation tendency propagates through the film and leads to a layer structure at low temper…