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  • 1
    Electronic Resource
    Electronic Resource
    Freie mitteilungen (1995)
    Springer
    Archives of gynecology and obstetrics 256 (1995), S. S208 
    Details
    ISSN: 1432-0711
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02201961
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  • 2
    Electronic Resource
    Electronic Resource
    Orientational order and rotational dynamics of the amide ions in potassium amide. I. Neutron diffraction (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2363-2373 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potassium amide (KNH2/KND2) is an ionic molecular crystal. The amide ions(NH2−/ND2−)—isoelectronic with the water molecule OH2—display orientational disorder in the cubic and tetragonal high–temperature phases. In the monoclinic low–temperature phase they are orientationally ordered. We investigated the deuterated compound KND2 in all three phases using high resolution neutron powder diffraction and determined the time–averaged probability density function of the deuterons in detail. The structure of the intermediate tetragonal phase was solved, and deviations of the reorientations of the amide ions in the cubic phase from free rotational diffusion were quantified. From the structural properties of the different phases of KND2 and the structural changes at the phase transitions conclusions on the respective dynamics of the amide ions can be drawn. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475052
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  • 3
    Electronic Resource
    Electronic Resource
    Symmetric diblock copolymers in thin films. I. Phase stability in self-consistent field calculations and Monte Carlo simulations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5241-5250 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the phase behavior of symmetric AB diblock copolymers confined into a thin film. The film boundaries are parallel, impenetrable and attract the A component of the diblock copolymer. Using a self-consistent field technique [M. W. Matsen, J. Chem. Phys. 106, 7781 (1997)], we study the ordered phases as a function of incompatibility χ and film thickness in the framework of the Gaussian chain model. For large film thickness and small incompatibility, we find first order transitions between phases with different number of lamellae which are parallel oriented to the film boundaries. At high incompatibility or small film thickness, transitions between parallel oriented and perpendicular oriented lamellae occur. We compare the self-consistent field calculations to Monte Carlo simulations of the bond fluctuation model for chain length N=32. In the simulations we quench several systems from χN=0 to χN=30 and monitor the morphology into which the diblock copolymers assemble. Three film thicknesses are investigated, corresponding to parallel oriented lamellae with 2 and 4 interfaces and a perpendicular oriented morphology. Good agreement between self-consistent field calculations and Monte Carlo simulations is found. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479778
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  • 4
    Electronic Resource
    Electronic Resource
    Symmetric diblock copolymers in thin films. II. Comparison of profiles between self-consistent field calculations and Monte Carlo simulations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5251-5258 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of lamellar phases of symmetric AB diblock copolymers in a thin film is investigated. We quantitatively compare the composition profiles and profiles of individual segments in self-consistent field calculations with Monte Carlo simulations in the bond fluctuation model for chain length N=32 and χN=30. Three film thicknesses are investigated, corresponding to parallel oriented lamellae with 2 and 4 interfaces and a perpendicular oriented morphology. Taking account of capillary waves, we find good quantitative agreement between the Monte Carlo simulations and the self-consistent field calculations. However, the fluctuations of the local interfacial position are strongly suppressed by confinement and mutual interactions between lamellae. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479823
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  • 5
    Electronic Resource
    Electronic Resource
    Interfaces between highly incompatible polymers of different stiffness: Monte Carlo simulations and self-consistent field calculations (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10764-10776 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate interfacial properties between two highly incompatible polymers of different stiffness. The extensive Monte Carlo simulations of the binary polymer melt yield detailed interfacial profiles and the interfacial tension via an analysis of capillary fluctuations. We extract an effective Flory–Huggins parameter from the simulations, which is used in self-consistent field calculations. These take due account of the chain architecture via a partial enumeration of the single chain partition function, using chain conformations obtained by Monte Carlo simulations of the pure phases. The agreement between the simulations and self-consistent field calculations is almost quantitative, however, we find deviations from the predictions of the Gaussian chain model for high incompatibilities or large stiffnesses. The interfacial width at very high incompatibilities is smaller than the prediction of the Gaussian chain model, and decreases upon increasing the statistical segment length of the semiflexible component. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474192
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of long-range forces on the interfacial profiles in thin binary polymer films (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 1221-1229 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the effect of surface fields on the interfacial properties of a binary polymer melt confined between two parallel walls. Each wall attracts a different component of the blend by a nonretarded van der Waals potential. An interface which runs parallel to the surfaces is stabilized in the center of the film. Using extensive Monte Carlo simulations we study the interfacial properties as a function of the film thickness, the strength of the surface forces, and the lateral size over which the profiles across the film are averaged. We find evidence for capillary wave broadening of the apparent interfacial profiles. However, the apparent interfacial width cannot be described quantitatively by a simple logarithmic dependence on the film thickness. The Monte Carlo simulations reveal that the surface fields give rise to an additional reduction of the intrinsic interfacial width and an increase of the effective interfacial tension upon decreasing the film thickness. These modifications of the intrinsic interfacial properties are confirmed by self-consistent field calculations. Taking account of the thickness dependence of the intrinsic interfacial properties and the capillary wave broadening, we can describe our simulation results quantitatively. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478164
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  • 7
    Electronic Resource
    Electronic Resource
    Orientational order and rotational dynamics of the amide ions in potassium amide. II. Quasielastic neutron scattering (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 3559-3567 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ionic molecular crystal potassium amide (KNH2) was investigated by means of quasielastic incoherent neutron scattering (QNS). In the orientationally disordered cubic and tetragonal high–temperature phases as well as in the ordered monoclinic phase reorientational motions of the amide ions (NH2−) are resolved in a frequency range of three orders of magnitude. The QNS spectra are well explained by reorientational models for each phase. Furthermore, the results are compared to structural data and findings of other spectroscopic methods. Finally, a consistent picture of structure and dynamics of all three phases of potassium amide is obtained. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476951
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  • 8
    Electronic Resource
    Electronic Resource
    Monte Carlo simulations of copolymers at homopolymer interfaces: Interfacial structure as a function of the copolymer density (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 5370-5379 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: By means of extensive Monte Carlo simulations of the bond fluctuation model, we study the effect of adding AB diblock copolymers on the properties of an interface between demixed homopolymer phases. The parameters are chosen such that the homopolymers are strongly segregated, and the whole range of copolymer concentrations in the two phase coexistence region is scanned. We compare the "mushroom" regime, in which copolymers are diluted and do not interact with each other, with the "wet brush" regime, where copolymers overlap and stretch, but are still swollen by the homopolymers. A "dry brush" regime is never entered for our choice of chain lengths. "Intrinsic" profiles are calculated using a block analysis method introduced by us in earlier work. We discuss density profiles, orientational profiles, and contact number profiles. In general, the features of the profiles are similar at all copolymer concentrations, however, the profiles in the concentrated regime are much broader than in the dilute regime. The results compare well with self-consistent field calculations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478432
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  • 9
    Electronic Resource
    Electronic Resource
    Liquid–vapor asymmetry in pure fluids: A Monte Carlo simulation study (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 2562-2573 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monte Carlo simulations within the grand canonical ensemble are used to obtain the joint distribution of density and energy fluctuations pL(ρ,u) for two model fluids: a decorated lattice gas and a polymer system. In the near critical region the form of pL(ρ,u) is analyzed using a mixed field finite-size-scaling theory that takes account of liquid–vapor asymmetry. Field mixing transformations are performed that map pL(ρ,u) onto the joint distribution of critical scaling operators p˜=(x,y) appropriate to the Ising fixed point. Carrying out this procedure permits a very accurate determination of the critical point parameters. By forming various projections of p˜=(x,y), the full universal finite-size spectrum of the critical density and energy distributions of fluids is also obtained. In the sub-critical coexistence region, an examination is made of the influence of field mixing on the asymmetry of the density distribution. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468686
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  • 10
    Electronic Resource
    Electronic Resource
    Bulk and interfacial thermodynamics of a symmetric, ternary homopolymer–copolymer mixture: A Monte Carlo study (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8885-8901 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results of a Monte Carlo simulation of a dense blend, comprising two incompatible homopolymers and a symmetric diblock copolymer, all of the same degree of polymerization. The simulations, in the framework of the bond fluctuation model, yield information on the phase diagram. At high temperatures the copolymer dilutes the homopolymer blend and shifts the critical temperatures of the demixing transition to lower temperatures. The line of second order transitions ends in a tricritical point, below which there is three-phase coexistence between two homopolymer-rich phases and a spatially structured copolymer-rich one. The simulations indicate that this latter phase is a microemulsion at intermediate incompatibility, and a lamellar phase at high incompatibility. Using a multimagnetic reweighting scheme, we independently determine the reduction of the interfacial tension and the copolymer excess at the interface between the coexisting homopolymer-rich phases. The bending rigidity is estimated by measuring the spectrum of interfacial fluctuations. We outline a method to determine the interaction between copolymer monolayers, and find that in the two-phase region it is attractive and its range increases upon addition of copolymers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472618
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