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  • 1
    Electronic Resource
    Electronic Resource
    Lattice model of self-assembly (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5473-5485 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A microscopic lattice model of two-component mixtures of water and amphiphile is introduced. The model is defined on a simple cubic lattice, the vertices of which are occupied by Ising and Heisenberg degrees of freedom which model water- and amphiphile-filled cubes. The orientations of the lipid molecules are described by the directions of the Heisenberg spin–vectors. Microscopic interactions between two water-filled cubes, two lipid-filled cubes, or a water- and a lipid-filled cube are related to the coupling constants of the model. In this paper we discuss the zero-temperature states of the model and, for some parts of the parameter space, these are explicitly constructed from local octahedral clusters of the cubic lattice. We then introduce a mean-field theory that preserves the full symmetry of the Hamiltonian, and thereby construct the global phase diagrams for different choices of the coupling parameters. In the conclusions to our paper we comment on other theoretical methods of solution being applied to the present Hamiltonian.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458526
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  • 2
    Electronic Resource
    Electronic Resource
    A lattice model description of amphiphilic mixtures. I. Equilibrium properties (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3152-3169 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A three-component lattice model with unit-vector orientations at the lattice sites is presented. The model describes ternary mixtures of oil, water, and amphiphile, and in particular the microemulsion phase. The phase diagram of the model is derived using mean-field theory and simulation. It is shown that the results of Monte Carlo simulations of sufficiently large systems show remarkable agreement with experiment. In particular, the present model reproduces the mesoscopic order of the microemulsion phase. The structure of the microemulsion is understood in terms of the liquid-crystalline phases adjacent to it on the phase diagram and the nature of the phase transitions that occur between them. The behavior of the system when the ratio of oil to water is changed is investigated and the percolation threshold is described. A method for carrying out dynamical simulations is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461958
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  • 3
    Electronic Resource
    Electronic Resource
    Viscosity of self-assembled fluids (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7695-7698 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We consider a Hamiltonian for a complex fluid. The linear excess bulk viscosity due to a spatially varying order parameter is investigated. We calculate the dependence of the excess viscosity Δη, on the fundamental parameters d and ξ, everywhere within the disordered phase (d being the domain size of water or oil and ξ being the correlation length between domains). It is found that there is a crossover region in the isotropic disordered phase of this model. More specifically, in the structured region of the isotropic disordered phase Δη grows as ξ3 in the vicinity of disordered-lamellar transition. This is quite distinct from the behavior of the excess viscosity in the unstructured region where Δη grows as ξ in the vicinity of the order-disorder transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463489
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  • 4
    Electronic Resource
    Electronic Resource
    A mean field approach to the structure of polyelectrolytes (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5352-5361 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe a variational mean field study of polyelectrolyte expansion based on the application of the Gibbs–Bogoliubov inequality and a generalized Gaussian trial Hamiltonian. The screened electrostatic interactions among the charged beads on the polyion are approximated by a pairwise additive Yukawa potential while we treat the excluded volume effects in terms of the Dirac δ function in the way usual in studies of neutral polymers. Expressing the Hamiltonian in terms of Fourier components, the variational procedure yields a set of Euler equations that are analyzed by the method of dominant balance to study the scaling regimes in various limiting situations. The method predicts correct scaling laws for weakly screened polyelectrolytes, dominated by long-ranged Coulombic repulsions. At strong screening or low degrees of ionization, when the polymer resembles a self-avoiding walk, the calculations overestimate the scaling exponent, the value of ∼4/3 replacing the Flory value, a deficiency known from earlier applications of the theory to nonionic macromolecules. The numerical solution to the Euler equations is used to calculate the mean square distances between monomer pairs in cyclic polyions as functions of the relative distance along the polymer backbone. Effects of the degree of polymerization and electrolyte screening are studied and the difficulties in providing a general numerical solution to the variational problem are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465979
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis of dynamic light scattering of poly(N-isopropylacrylamide) across the collapse transition (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 711-720 
    Details
    ISSN: 0392-6737
    Keywords: Polymer reactions and polymerization ; Brillouin and Rayleigh scattering ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We analyse data from the dynamic light scattering of poly(N-isopropylacrilamide) in water solution as we cross the collapse transition. Experimental data are interpreted by the Gaussian self-consistent Zimm model that takes into account two- and three-body excluded-volume effects, and Oseen hydrodynamic interactions, as well as by the standard cumulant and Contin analyses. By fitting the dynamic structure factor we extract the temperature dependence of the diffusion coefficientD and the first relaxation time τ1 across the collapse transition for a range of scattering angles. The relaxation time τ1 possesses a characteristic peak at about 32.4 °C due to slowing of the internal motions of the polymer at the theta-point, and a minimum at 33.4 °C. We interpret this as a combination of collapse closely followed by the growth of critical correlations. At large scattering angles we reach the universalk 3 regime, and observe that this behaviour vanishes at the onset of collapse transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456716
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  • 6
    Electronic Resource
    Electronic Resource
    Novel approaches to parallelism in soft-matter problems (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 831-834 
    Details
    ISSN: 0392-6737
    Keywords: Renormalization-group, fractal and percolation studies of phase transitions ; Chemical kinetics: Computational modelling: simulation ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We outline a novel method of exploiting distributed computational resources to study problems in soft-matter science. We have applied our method to simulations of polymers, including hydrodynamic effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456731
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical and experimental approaches to kinetics at the collapse transition of a homopolymer (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 675-687 
    Details
    ISSN: 0392-6737
    Keywords: Polymers, elastomers, and plastics ; Polymer reactions and polymerization ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We discuss some recent theoretical studies of the kinetics of the collapse transition in homopolymers. An isolated polymer is modelled using computer simulation, and a time-dependent mean-field theory. The mean-field theory is analysed analytically for early stages, and for short polymers the equations are studied numerically. The results of simulation and theory are compared yielding, we argue, a consistent physical picture. Quantitative comparisons are not yet given, but seem relatively promising.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456712
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  • 8
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    Universal nature of the nematic-to-isotropic transition in solutions of discotic micelles (1991)
    American Physical Society
    Details
    Publication Date: 1991-06-03
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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  • 9
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    Dynamical lattice-model simulation (1993)
    American Physical Society
    Details
    Publication Date: 1993-05-01
    Print ISSN: 1063-651X
    Electronic ISSN: 1095-3787
    Topics: Physics
    Published by American Physical Society
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  • 10
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    Sine-Gordon renormalization of the orientational roughening transition (1990)
    American Physical Society
    Details
    Publication Date: 1990-09-01
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Physical Society
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