Search results for "Gyration"
showing 10 items of 118 documents
Comb-Branched Polymers: Monte Carlo Simulation and Scaling
1996
The Monte Carlo simulation technique (the bond fluctuation model) has been used for the study of the equilibrium conformations of comb-branched polymers consisting of a long flexible main chain and side chains grafted at a regular separation onto the main chain. The solvent has been supposed to be good (athermal) for the main and side chains. The global conformation and the gyration radius of the polymer, as well as the local conformational structure of the comb, have been analyzed as functions of the length of the side chains and spacers. The effect of induced rigidity of the comb due to the interaction between side chains has been observed. We have found the results of the simulation to b…
Frictional Drag Mechanisms between Polymer-Bearing Surfaces
2001
The fundamental features of friction between two polymer-bearing surfaces in relative sliding motion are investigated by molecular dynamics simulation. Adsorbed and grafted polymers are considered in good and bad solutions. The solvent is not treated explicitly but indirectly in terms of a Langevin thermostat. In both systems, we observe shear thinning that is attributed to an orientation of the radius of gyration along the sliding direction. This effect is particularly strong for surfaces bearing polymer brushes. In this case, the shear stresses are mainly determined by the degree of the interpenetration of brushes.
Polymer brushes in solvents of variable quality: Molecular dynamics simulations using explicit solvent
2007
The structure and thermodynamic properties of a system of end-grafted flexible polymer chains grafted to a flat substrate and exposed to a solvent of variable quality are studied by molecular dynamics methods. The macromolecules are described by a coarse-grained bead-spring model, and the solvent molecules by pointlike particles, assuming Lennard-Jones-type interactions between pairs of monomers (epsilon(pp)), solvent molecules (epsilon(ss)), and solvent monomer (epsilon(ps)), respectively. Varying the grafting density sigma(g) and some of these energy parameters, we obtain density profiles of solvent particles and monomers, study structural properties of the chain (gyration radius componen…
Interfacial properties of glassy polymer melts: A Monte Carlo study
1996
The properties of the interface between a polymer melt and a solid wall are studied over a wide range of temperatures by dynamic Monte Carlo simulations. It is shown that in the supercooled state near the glass transition of the melt an “interphase” forms, the structure of which is influenced by the wall. The thickness of this interphase is determined from the monomer density profile near the surface and is strongly temperature dependent. At low glass-like temperatures it is larger than the bulk radius of gyration of the chains.
Conformational studies of bottle-brush polymers absorbed on a flat solid surface.
2010
The adsorption of a bottle-brush polymer end-grafted with one chain end of its backbone to a flat substrate surface is studied by Monte Carlo simulation of a coarse-grained model, that previously has been characterized in the bulk, assuming a dilute solution under good solvent conditions. Applying the bond fluctuation model on the simple cubic lattice, we vary the backbone chain length $N_b$ from $N_b=67$ to $N_b = 259$ effective monomeric units, the side chain length $N$ from N=6 to N=48, and the grafting density $\sigma=1$, i.e., parameters that correspond well to the experimentally accessible range. When the adsorption energy strength $\epsilon$ is varied, we find that the adsorption tra…
Chain linear dimensions in the surface-enriched layer of polymer mixtures
1992
We calculate the mean-square end-to-end distances and mean-square gyration radii using the bond fluctuation model for a binary polymer blend in the presence of a wall by Monte Carlo simulation. In the bulk, the size of the minority, low-concentration polymer species is compressed compared to the majority one. In the vicinity of the wall, where the minority polymer concentration is enriched due to attraction from the wall, the dimensions of the two types of polymers are approximately equal and are essentially the same as in an athermal polymer melt. Thus, the geometric constraint is more important to the structure of the polymers than the polymer-polymer and polymer-wall interactions.
Reibungsverhalten und Trägheitsradien von oligomeren Polypropylenglykolen
1971
Die Ergebnisse von Viskositats- und Diffusionsmessungen an oligomeren Propylenglykolen in Aceton und Benzol werden benutzt, um nach den verschiedenen Theorien die viskosimetrischen und Reibungstragheitsradien zu ermitteln. Ein Vergleich mit direkt durch Streuversuche mit der Rontgenkleinwinkelmethode gefundenen Tragheitsradien zeigt die Gultigkeit der klassischen Viskositatstheorien, wahrend die gleichen Theorien bei der Reibung versagen. Aus [f] = 16,4 · R erhalt man jedoch wie bei Hochpolymeren auch fur Oligomere vernunftige Tragheitsradien. Results of viscometric and frictional measurements on oligomeric propylene glycols in acetone and benzene have been used to calculate the values of v…
Stratification in Drying Polymer–Polymer and Colloid–Polymer Mixtures
2017
Drying polymer-polymer and colloid-polymer mixtures were studied using Langevin dynamics computer simulations. Polymer-polymer mixtures vertically stratified into layers, with the shorter polymers enriched near the drying interface and the longer polymers pushed down toward the substrate. Colloid-polymer mixtures stratified into a polymer-on-top structure when the polymer radius of gyration was comparable to or smaller than the colloid diameter, and a colloid-on-top structure otherwise. We also developed a theoretical model for the drying mixtures based on dynamical density functional theory, which gave excellent quantitative agreement with the simulations for the polymer-polymer mixtures a…
Acrylic Graft Copolymers Via Macromonomers
1995
Comb-shaped poly(methyl methacrylate) (PMMA) and PMMA grafted with poly(nbutyl acrylate) (PnBuA) were prepared by radical copolymerisation of ω-methacryloyl-PMMA with MMA and nBuA, respectively. The comb-shaped PMMA is characterised with respect to radius of gyration by using GPC equipped with a multi-angle laser light scattering detector. The radical copolymerisation of the macromonomer with nBuA in toluene follows complex kinetics. The dependence of the relative reactivity of the macromonomer on absolute concentration and on the ratio of comonomers may be explained by preferential solvation of comonomers by segments of their own kind (“bootstrap effect”) or even micelle formation. However…
Herstellung, charakterisierung und lösungseigenschaften von einheitlichen styrol-α-methylstyrol block-copolymeren
1977
An improved anionic polymerization technique for the preparation of highly uniform styrene/α-methylstyrene linear two-block copolymers is described. Three sets of samples with molecular weights M were prepared under equal experimental conditions, namely polystyrenes (2 · 105 < M < 3 · 106), poly(α-methylstyrene)s (7 · 104 < M < 4 · 106), and block copolymers (2 · 105 < M < 2,5 · 106). Ultracentrifugation in a density-gradient does not show any chemical heterogeneities in the block copolymers. The molecular polydispersity U = Mw/Mn–1 is U = 0,03 or less as estimated from GPC-measurements. The high molecular and chemical homogeneity of the block copolymers and the optical similarity of the tw…