Search results for "soft"
showing 10 items of 9809 documents
Structure and dynamics of thin polymer films: a case study with the bond-fluctuation model
2002
Abstract This paper reports Monte Carlo simulation results of a polymer melt of short, non-entangled chains which are embedded between two impenetrable walls. The melt is simulated by the bond-fluctuation lattice model under athermal conditions, i.e. only excluded volume interactions between the monomers and between the monomers and the walls are taken into account. In the simulations, the wall separation is varied from about one to about 15 times the bulk radius of gyration R g . The confinement influences both static and dynamic properties of the films: Chains close to the walls preferentially orient parallel to it. This parallel orientation decays with increasing distances from the wall …
Anomalous diffusion in polymer melts
2002
Abstract We present a study of the anomalous diffusion regimes in polymer melt dynamics performing a Monte Carlo (MC) simulation of the bond-fluctuation lattice model. Special emphasis is laid on the crossover from a Rouse-like motion to the behavior predicted by reptation theory. For the longest chains of N=400 the high statistical accuracy of the data allows for clear identification of the subdiffusive regimes in the center of mass motion and the monomer displacement. They are well compatible with those predicted by reptation theory. Furthermore a detailed analysis of the different short time anomalous diffusion regimes in the melt dynamics of polymer chains is presented and it is shown t…
Interfaces in immiscible polymer blends: A Monte Carlo simulation approach on the CRAY T3E
1999
Polymeric materials pose a challenge for Monte Carlo simulations because of the widely spread length and time scales involved. Using large scale computer simulations we investigate the interfacial structure in a partially compatible polymer mixture. The problem is studied in the framework of a coarse grained lattice model - the bond fluctuation model on the simple cubic lattice, choosing N = 32 and lattice linear dimensions L × L × D up to 512 × 512 × 64. We employ a two dimensional geometric decomposition scheme to implement this algorithm on the CRAY T3E. The algorithm scales very well with the number of processors. The structure of polymer coils near interfaces between coexisting phases …
Unified Thermodynamic Modeling of Polymer Solutions: Polyelectrolytes, Proteins, and Chain Molecules
2013
The thermodynamic description of the systems specified in the title requires in general dissimilar theories. This contribution presents an approach that is capable of modeling all of them with a maximum of three adjustable parameters. The Ansatz starts from the Flory–Huggins theory and extends it in a 2-fold manner: The number of segments assigned to the solvent is no longer one but treated as an adjustable parameter to account for the differences in the molecular geometries and in the free volumes of the components. Furthermore, the modeling allows for effects resulting from ternary contacts of the solvent/polymer/polymer type. Examination of the acquired thermodynamic expressions by means…
Structure and dynamics of grafted polymer layers: A Monte Carlo simulation
1991
The bond fluctuation model of polymer chains on lattices is used to study layers of polymers anchored with one end at a hard wall, assuming good solvent conditions and repulsive interactions between the monomers and the wall. Chain lengths from N=10 to N=80 and grafting densities σ from 0.025 to 0.20 are considered, both for the ‘‘quenched’’ case, where the anchor points are kept fixed at randomly chosen surface sites, and the ‘‘annealed’’ case, where lateral diffusion of the anchored ends at the wall is considered. Profiles of monomer density and free end density, chain linear dimensions parallel and perpendicular to the wall, as well as corresponding mean square displacements of inner and…
Monte Carlo simulations of chain dynamics in polymer brushes
1994
The bond-fluctuation model of polymer chains has been used to study layers of end-grafted polymers anchoring at repulsive walls for a broad range of chain length, grafting densities and solvent quality. The dynamics of monomers and associated relaxation times are investigated and interpreted by phenomenological theories and scaling arguments. The case is also considered where a chain is cut off from its anchor point and the chain is subsequently expelled from the brush. Both the velocity with which the chain leaves the brush and the associated conformational changes (chain contraction etc.) are analysed and interpreted in terms of recent theoretical concepts.
A comparison of neutron scattering studies and computer simulations of polymer melts
2000
Abstract Neutron scattering and computer simulations are powerful tools for studying structural and dynamical properties of condensed matter systems in general and of polymer melts in particular. When neutron scattering studies and quantitative atomistic molecular dynamics simulations of the same material are combined, synergy between the methods can result in exciting new insights into polymer melts not obtainable from either method separately. We present here an overview of our recent efforts to combine neutron scattering and atomistic simulations in the study of melt dynamics of polyethylene and polybutadiene. Looking at polymer segmental motion on a picosecond time scale, we show how at…
Fractal calibration in size-exclusion chromatography
2003
Abstract The elution behaviour of different polymer–solvent systems in three types of organic columns for SEC has been compared and interpreted. The experimental data show that the classical universal calibration is not accomplished. Deviations from a unique curve are observed due to the binary and ternary interactions between the components of the system (solvent, polymer and gel) which results on secondary mechanisms accompanying the main pure or “ideal” SEC separation mechanism. Both, enthalpic and entropic effects are interpreted in terms of the swelling and crosslinking degrees of the gel packings, and are also related with the fractal characteristics of their surfaces, such as the fra…
Osmotic pressure of catenanes in solution
1989
We propose a nonuniversal scaling for the osmotic pressure in the case of concatenating ring polymers. The size exponent depends on the molecular weight of the catenans. The effect is more significant the shorter and the stiffer the molecules are.
Energy-stable linear schemes for polymer-solvent phase field models
2017
We present new linear energy-stable numerical schemes for numerical simulation of complex polymer-solvent mixtures. The mathematical model proposed by Zhou, Zhang and E (Physical Review E 73, 2006) consists of the Cahn-Hilliard equation which describes dynamics of the interface that separates polymer and solvent and the Oldroyd-B equations for the hydrodynamics of polymeric mixtures. The model is thermodynamically consistent and dissipates free energy. Our main goal in this paper is to derive numerical schemes for the polymer-solvent mixture model that are energy dissipative and efficient in time. To this end we will propose several problem-suited time discretizations yielding linear scheme…