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  • 1
    Digitale Medien
    Digitale Medien
    The effect of attractions on the structure of fused sphere chains confined between surfaces (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1608-1614 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The effect of attractive interactions on the behavior of polymers between surfaces is studied using Monte Carlo simulations. The molecules are modeled as fused sphere freely rotating chains with fixed bond lengths and bond angles; wall–fluid and fluid–fluid site–site interaction potentials are of the hard sphere plus Yukawa form. For athermal chains the density at the surface (relative to the bulk) is depleted at low densities and enhanced at high densities. The introduction of a fluid–fluid attraction causes a reduction of site density at the surface, and an introduction of a wall–fluid attraction causes an enhancement of site density at the surface, compared to when these interactions are absent. When the wall–fluid and fluid–fluid attractions are of comparable strength, however, the depletion mechanism due to the fluid–fluid attraction dominates. The center of mass profiles show the same trends as the site density profiles. Near the surface, the parallel and the perpendicular components of chain dimensions are different, which is explained in terms of a reorientation of chains. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.479421
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  • 2
    Digitale Medien
    Digitale Medien
    Computer simulations and integral equation theory for the structure of salt-free rigid rod polyelectrolyte solutions: Explicit incorporation of counterions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11599-11607 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The static structure of salt-free solutions of rod-like polyelectrolyte solutions is studied using Monte Carlo simulations and integral equations. The polymer reference interaction site model theory with the reference Laria–Wu–Chandler closure is found to be in good agreement with the simulations for the polyion–polyion and counterion–counterion correlation functions, and in qualitative agreement with the simulations for the counterion–polyion correlation functions. The effect on the polyion concentration on the counterion distribution is found to be important at low concentrations and becomes more significant when the Bjerrum length or degree of polymerization are increased. The theory is in almost quantitative agreement with the simulations for the static structure factor. The theory predicts that all three partial structure factors display low angle peaks at roughly the same wave vectors. The position and intensity of the peak in the polyion structure factor is insensitive to the Bjerrum length. These predictions are consistent with recent experiments. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.479099
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  • 3
    Digitale Medien
    Digitale Medien
    Density functional theory of polymers: A Curtin-Ashcroft type weighted density approximation (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 3269-3275 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A density functional theory is presented that combines an exact expression for the ideal gas free energy functional with a weighted density approximation for the excess free energy functional. The weighting function required in the theory is obtained from the Curtin-Ashcroft recipe, with a bulk fluid direct correlation function from the polymer reference interaction site model integral equation theory. The theory is in quantitative agreement with computer simulations for the density profiles of freely jointed tangent sphere hard chains at a hard wall, about as accurate as the Curtin-Ashcroft theory is for hard spheres at a hard wall. For a more realistic fused-sphere chain model with fixed bond angles and bond lengths, the theory is in excellent agreement with simulations at low and intermediate densities but overestimates the magnitude of layering at high densities for short chains. The theory becomes more accurate as the chain length is increased. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.476918
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  • 4
    Digitale Medien
    Digitale Medien
    Monte Carlo simulations and self-consistent integral equation theory for polyelectrolyte solutions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 5437-5443 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The static structure and conformational properties of salt-free polyelectrolyte solutions are studied using many-chain Monte Carlo simulations and integral equations. The polymer molecules are modeled as freely jointed tangent sphere chains with a hard sphere plus screened Coulomb potential between the beads. Monte Carlo simulations are for the most part in agreement with previous molecular dynamics simulations of a related model of polymers but the present work facilitates an unambiguous comparison between theory and simulation. An integral equation theory is implemented where the properties of the polymer are obtained from a single chain simulation where the beads interact via the bare potential plus a self-consistently determined solvation potential. The theory overestimates the degree of liquidlike order and underestimates the size of the chains (when compared to many chain simulations) especially for long chains and high densities. A more approximate theory that employs a thread model for the polymers is actually more accurate. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.478439
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  • 5
    Digitale Medien
    Digitale Medien
    Theory for chain conformations and static structure of dilute and semidilute polyelectrolyte solutions (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 1184-1192 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A theory is presented for the conformational properties and static structure of polyelectrolyte solutions. The theory combines field theoretic methods with liquid-state theory, and incorporates screening from counterions and polyions through a self-consistently determined solvation potential. Predictions for the size of the polymer molecules and the static structure factor are in good agreement with molecular dynamics simulations over the entire concentration regime, with no adjustable parameters. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.475480
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  • 6
    Digitale Medien
    Digitale Medien
    Integral equation theory of solutions of rigid polyelectrolytes (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5706-5719 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The properties of dilute and semidilute solutions of rigid polyelectrolytes are investigated using integral equation theory. The theory predicts liquidlike structure on length scales of the order of the length of the molecules in dilute solution. This structure appears at concentrations much lower than the overlap threshold concentration, and disappears when the concentration is sufficiently high. Liquidlike order reappears at higher concentrations on a lengthscale of the order of the thickness of the rods. The predictions of the theory for the static structure factor in tobacco mosaic virus solutions are in good agreement with light scattering experiments in both dilute and semidilute solutions. The theory predicts that kmax∼ρν, where kmax is the position of the maximum in the structure factor and ρ is the concentration, with ν(approximate)1/3 and 1/2 in the dilute and semidilute regimes, respectively. These values are consistent with experimental results. Predictions are also presented for rigid starlike polymers. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.473590
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  • 7
    Digitale Medien
    Digitale Medien
    Forces between surfaces immersed in polyelectrolyte solutions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1797-1800 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A microscopic theory is presented for the behavior of polyelectrolyte solutions between surfaces. The theory predicts oscillatory forces between hydrophobic surfaces immersed in dilute salt-free polyelectrolyte solutions. The period of the oscillation, p, scales with concentration, ρ, as p∼ρ−1/3 and p∼ρ−1/2, in the dilute and semidilute solutions, respectively. With a small amount of excess salt, the oscillatory forces are replaced by a short-ranged, predominantly attractive force. Further addition of salt causes the force to become purely repulsive. These predictions can, in principle, be tested experimentally. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.479448
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  • 8
    Digitale Medien
    Digitale Medien
    Generalized van der Waals density functional theory for nonuniform polymers (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1579-1584 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A density functional theory is presented for the effect of attractions on the structure of polymers at surfaces. The theory treats the ideal gas functional exactly, and uses a weighted density approximation for the hard chain contribution to the excess free energy functional. The attractive interactions are treated using a van der Waals approximation. The theory is in good agreement with computer simulations for the density profiles at surfaces for a wide range of densities and temperatures, except for low polymer densities at low temperatures where it overestimates the depletion of chains from the surface. This deficiency is attributed to the neglect of liquid state correlations in the van der Waals term of the free energy functional. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.480706
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  • 9
    Digitale Medien
    Digitale Medien
    Conformational properties of isolated polyelectrolytes in poor solvents (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 676-681 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The conformational behavior of isolated polyelectrolytes in poor solvents is investigated using theory and computer simulation. DiMarzio's approach for the collapse transition in neutral polymers is extended to uniformly charged polymers [E. A. diMarzio, Macromolecules 17, 969 (1984)]. The theory predicts a discontinuous collapse transition with decreasing solvent quality in highly charged polymers. A discontinuous collapse transition is also observed when the charge fraction is decreased in very poor solvents. Monte Carlo simulations are reported for the collapse transition in a lattice model of polyelectrolytes. Under some conditions the distribution of polymer size is bimodal, consistent with the theory. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.478138
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  • 10
    Digitale Medien
    Digitale Medien
    Ion binding in tobacco mosaic virus solutions (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5162-5163 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The structure of salt-free solutions of tobacco mosaic virus particles is investigated using integral equations with the counterions incorporated explicitly. The results for the structure factor are identical to previous studies which used a Debye–Hückel approximation. The results are explained using a model of the particles as polyacids. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.477131
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