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  • 1
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    Effects of polymer stiffness on surface tension and pressure in confinement (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-08-11
    Description: We study the effect of chain rigidity on the behavior of semiflexible polymers in the vicinity of flat walls in a slit, and of surfactants at the liquid-liquid interface between immiscible liquids. Using molecular dynamics simulations, it is demonstrated that the impact of bending angle forces is particularly strong within the depletion layer at the phase boundary whereas at distance R e away from the interface, where R e is the mean distance between the ends of a semiflexible chain, the contribution of these non-local triplet interactions to pressure tensor virtually disappears. The present study also demonstrates that growing stiffness of the macromolecules leads to an increase in surface tension and total pressure.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Semiflexible polymers under good solvent conditions interacting with repulsive walls (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-05-04
    Description: Solutions of semiflexible polymers confined by repulsive planar walls are studied by density functional theory and molecular dynamics simulations, to clarify the competition between the chain alignment favored by the wall and the depletion caused by the monomer-wall repulsion. A coarse-grained bead-spring model with a bond bending potential is studied, varying both the contour length and the persistence length of the polymers, as well as the monomer concentration in the solution (good solvent conditions are assumed throughout, and solvent molecules are not included explicitly). The profiles of monomer density and pressure tensor components near the wall are studied, and the surface tension of the solution is obtained. While the surface tension slightly decreases with chain length for flexible polymers, it clearly increases with chain length for stiff polymers. Thus, at fixed density and fixed chain length, the surface tension also increases with increasing persistence length. Chain ends always are enriched near the wall, but this effect is much larger for stiff polymers than for flexible ones. Also the profiles of the mean square gyration radius components near the wall and the nematic order parameter are studied to clarify the conditions where wall-induced nematic order occurs.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Anomalous Fluctuations of Nematic Order in Solutions of Semiflexible Polymers (2016)
    American Physical Society (APS)
    Details
    Publication Date: 2016-05-07
    Description: Author(s): Sergei A. Egorov, Andrey Milchev, and Kurt Binder The nematic ordering in semiflexible polymers with contour length L exceeding their persistence length ℓ p is described by a confinement of the polymers in a cylinder of radius r eff much larger than the radius r ρ expected from the respective concentration of the solution. Large-scale molecular dynami… [Phys. Rev. Lett. 116, 187801] Published Thu May 05, 2016
    Keywords: Polymer, Soft Matter, Biological, Climate, and Interdisciplinary Physics
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society (APS)
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  • 4
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    Structure and dynamics of polymer melt confined between two solid surfaces: A molecular dynamics study (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-07-31
    Description: Using large scale molecular dynamics simulations we investigate the static and dynamic properties of a linear polymer melt confined between two solid surfaces. One of the walls is repulsive and the other is attractive wall. The bottom attractive wall is characterized by different degrees of roughness which is tuned by an array of short perpendicular rigid pillars with variable grafting density. We demonstrate that the conformations of polymers at the interfaces do not depend on substrate-polymer interactions, rather they show similar conformations of a single end-grafted chain under critical adsorption condition, consistent with the Silberberg's hypothesis. This observation is found to be in a good agreement with the analysis of the size distributions of trains, loops, and tails of melt chains at the walls known from the theoretical prediction of the end-grafted single chains at critical adsorption. Furthermore, we find that the pressure of the melt P N decreases as P N − P ∞ ∝ N − 1 with growing length of the chains N (where P ∞ is the extrapolated pressure for N → ∞). Moreover, the surface tension γ near both walls is found to follow γ N ∝ N −2/3 . Eventually, the lateral dynamics near rough surface drops suddenly when the separation between the neighboring pillars becomes smaller than 2 R g , where R g is the bulk radius of gyration.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    Semiflexible Polymers in Spherical Confinement: Bipolar Orientational Order Versus Tennis Ball States (2017)
    American Physical Society (APS)
    Details
    Publication Date: 2017-05-27
    Description: Author(s): Arash Nikoubashman, Daniel A. Vega, Kurt Binder, and Andrey Milchev Densely packed semiflexible polymers with contour length L confined in spheres with radius R of the same order as L cannot exhibit uniform nematic order. Depending on the chain stiffness (which we vary over a wide range), highly distorted structures form with topological defects on the sphere surfac… [Phys. Rev. Lett. 118, 217803] Published Fri May 26, 2017
    Keywords: Polymer, Soft Matter, Biological, Climate, and Interdisciplinary Physics
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society (APS)
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  • 6
    Electronic Resource
    Electronic Resource
    Random Walk in Cellular Media (1994)
    s.l. : American Chemical Society
    Langmuir 10 (1994), S. 4698-4702 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00024a051
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  • 7
    Electronic Resource
    Electronic Resource
    A model for adsorption of O on Mo(110): Phase transitions with nonuniversal behavior (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3958-3973 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A lattice-gas model for the phase transitions of O monolayers on Mo(110) with interactions ranging up to fifth neighbors, and including a three-particle term, is studied by Bragg–Williams mean-field theory and finite-size scaling of data from Monte Carlo simulations and numerical transfer-matrix calculations. Attention is focused on the p(2×2) phase whose symmetry is that of an XY model with cubic anisotropy. The order–disorder transition lines are shown to exhibit the predicted nonuniversal behavior, and possess tricritical points. A phenomenological finite-size scaling theory for the Monte Carlo order-parameter data in the pertinent case of a third-order coupling in the Landau free energy is established. The order–order transition line between the p(2×2) and (2×1) phases is found to consist of two parts, a first-order line at low temperature, and a line at higher temperatures, along which the model has a pure Kosterlitz–Thouless phase. Good agreement is established with an experimental phase diagram based on low-energy electron diffraction (LEED) data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460673
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  • 8
    Electronic Resource
    Electronic Resource
    Polymer melt droplets adsorbed on a solid wall: A Monte Carlo simulation (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 8610-8618 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a coarse-grained bead-spring model of flexible polymers, we study the contact angle of polymer melt droplets sitting at a flat structureless wall, when the strength ε of the adsorption potential Vwall(z)=ε/z3 is varied. For this purpose, droplets containing 2048 or 4096 monomers for chain lengths N=16 and N=32 were carefully equilibrated at temperatures in the range from 74% to 82% of the Theta temperature, and the density profile of these droplets both in the z direction perpendicular to the substrate surface and in the radial direction was obtained. Beyond a critical value of ε we find that the contact angle vanishes, i.e., the droplets spread out and form a flat film. Such flat polymer films are also studied with considerably more polymers (up to 24 576 monomers contained in the simulation box). It is shown that the density profile ρ(z) is affected by the hard wall (exhibiting the characteristic layering oscillations) up to about z=5 (measuring lengths in units of the length of an effective bond), while at larger z the profile is flat and has the melt density at that temperature, with an interface to the "gas" at about z=20. Analyzing the capillary wave spectrum of the interfacial fluctuations, the surface tension of the polymer melt is extracted. Via the anisotropy of the local pressure near the wall, the wall excess free energy of the polymer melt is found as well, and the Young equation is tested. Thus methods have been developed that allow a systematic study of polymer–wall interactions and wetting vs dewetting behavior. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1362164
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  • 9
    Electronic Resource
    Electronic Resource
    Dewetting of thin polymer films adsorbed on solid substrates: A Monte Carlo simulation of the early stages (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 1978-1989 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using an off-lattice bead–spring model of flexible polymer chains containing N=32 beads under bad solvent conditions, thin films of polymer melts are simulated. The films are confined between two parallel plates, the upper plate being purely repulsive while the lower plate exerts a short range attraction on the polymer layer so that a dense thin film is adsorbed on this plate for large enough attraction strength ε. Then "quenching experiments'' are simulated by suddenly reducing |ε| at time t=0 and monitoring the time evolution of the polymer film. While for large enough final values of |ε| only the density in the film decreases somewhat, but the film stays laterally homogeneous, for |ε| less than a critical value |εc| it is found that the film breaks up into droplets. The early stages of the time evolution of this process in the framework of a dynamic Monte Carlo simulation are studied both by recording the time dependence of the adsorbed amount, the average thickness of the layer, the distribution function of meansquare displacements, and with the help of snapshot pictures of the system configurations. Also equilibrium properties of the films are investigated including both collective properties such as density profiles and radial distribution functions, and single-chain properties such as parallel and perpendicular parts of meansquare gyration radii, in dependence on the adhesive strength |ε| of the substrate. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473341
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  • 10
    Electronic Resource
    Electronic Resource
    Adsorption of living polymers on a solid surface: A Monte Carlo simulation (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9161-9168 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effects of surface segregation in a polydisperse system of "living polymers,'' confined between parallel solid surfaces, are studied by means of a lattice Monte Carlo (MC) simulation. For given density and temperature the system is characterized by exponential distribution of chain lengths established in the process of reversible equilibrium polymerization. The results of the calculations show that entropic effects cause a rearrangement of the species with different length into an "onion shell'' structure. Thus for flexible chains preferential presence of shorter chains in the vicinity of the surface takes place, in contrast to the case of semi-rigid chains, when shorter chains deplete the region around the solid surface. In the case of adsorbing walls this surface segregation is enhanced. The study also reveals that isotherms of the adsorbed coverage and adsorbed amount are strongly influenced by the degree of chain stiffness. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471448
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