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  • American Institute of Physics  (26)
  • American Institute of Physics (AIP)  (21)
  • American Chemical Society  (4)
  • Canadian Science Publishing  (2)
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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
    Microscopic model of amphiphilic assembly (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6393-6403 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A microscopic model of lyotropic systems is presented. Amphiphile and water molecules are described by simple intermolecular potentials which correctly include important excluded volume effects and the relative energy scales in the system. The present model represents an attempt to bridge the gap between more primitive lattice models and highly complex all-atom descriptions of amphiphilic systems. A constant-temperature molecular dynamics study in which the divergence of the pressure tensor is constrained to zero is discussed. Preliminary calculations on the phase diagram, order parameters, and dynamical observables of the model are reported. Some comments on improvements to the model and the theoretical techniques used to study it are made in the final section of the paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457407
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  • 3
    Electronic Resource
    Electronic Resource
    Phase diagram of a lattice microemulsion model (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5149-5156 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We derive the phase diagram of a recently proposed model of microemulsions. The model is equivalent to an Ising model with nearest-neighbor interaction parameter J, diagonal-neighbor interaction parameter 2M, and further-neighbor interaction parameter M. We find the regions of stability of the various phases in the j(=J/kT), m(=M/kT) plane, both by solution of the mean-field equations at finite j and m and by an exact analysis at T=0(m→−∞, j→±∞). The disordered (paramagnetic) region is bounded by an ellipse and two of its tangents. We concentrate our attention on the phases of periodic structure near the paramagnetic boundary, on the low-temperature phases, and on the connections between them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454669
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Effects of subgrain structures on the optical homogeneity of Tl3AsSe3 single crystals (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 827-830 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Studies of subgrain structures in Tl3AsSe3 have been performed by x-ray topography. Birefringent interference patterns show that a direct correlation exists between the subgrain structures and the optical homogeneity of the crystals. A quantitative measurement of lattice misorientation was performed from the interference patterns and compared with x-ray rocking measurements. The origin of the subgrains is also discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341932
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  • 8
    Electronic Resource
    Electronic Resource
    Kinetic laws at the collapse transition of a homopolymer (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3338-3347 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results from numerical analysis of the equations derived in the Gaussian self-consistent method for kinetics at the collapse transition of a homopolymer in dilute solution. The kinetic laws are obtained with and without hydrodynamics for different quench depths and viscosities of the solvent. Some of our earlier analytical estimates are confirmed, and new ones generated. Thus the first kinetic stage for small quenches is described by a power law decrease in time of the squared radius of gyration with the universal exponent αi=9/11 (7/11) with (without) hydrodynamics. We find the scaling laws of the characteristic time of the coarsening stage, τm∼Nγm, and the final relaxation time, τf∼Nγf, as a function of the degree of polymerization N. These exponents are equal to γm=3/2, γf=1 in the regime of strong hydrodynamic interaction, and γm=2, γf=5/3 without hydrodynamics. We regard this paper as the completion of our work on the collapse kinetics of a bead and spring model of a homopolymer, but discuss the possibility of studying more complex systems. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471096
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  • 9
    Electronic Resource
    Electronic Resource
    New orientationally ordered phases of a homopolymer (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 336-341 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results of Monte Carlo simulations of a homopolymer with three-body interactions on a lattice. At equilibrium we find three collapsed phases with different orientational order. The first one may be described as a conventional phase with effective three-body attraction. Two other phases are observed in the region of the phase diagram corresponding to three-body repulsion. The second phase is characterized by local orientational order within the globule. The third one possesses global orientational order and it appears to be analogous to nematic phase of a liquid crystal. Kinetics of the collapse transition to the phase III is crucially different from that of phase I and II due to formation of clusters with different orientations at the intermediate stage. This is the origin of a metastable long-lived state in kinetics. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470832
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  • 10
    Electronic Resource
    Electronic Resource
    Freezing transition temperature of random copolymers (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 9886-9887 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We use the mean field replica theory to analyze the dependence of the freezing transition temperature on the composition and coupling constants for two letter random copolymers. Gaussian disorder is considered. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469957
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