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  • 1
    Electronic Resource
    Electronic Resource
    Neutron reflectivity study of block copolymers adsorbed from solution (1990)
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 3860-3864 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00218a023
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  • 2
    Electronic Resource
    Electronic Resource
    The effects of substrate roughness on ultrathin water films (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7505-7515 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Real surfaces are rough and chemically heterogeneous on many length scales and wetting phenomena on these surfaces are affected by this inhomogeneous nature. We have used x-ray reflectivity to examine the structure of static precursing films which precede the macroscopic meniscus of water on glass. We have examined the thickness of the film, the roughness of the interfaces bounding the film, and the conformality or correlations between the roughness features of these bounding interfaces. The wetting film consists of three basic components: the bulk meniscus, a thin (≤100 A(ring)) precursing wetting film which has a sudden termination, and beyond that, a much thinner film characteristic of the glass surface in contact with water vapor only. The roughness and chemical heterogeneity of the solid manifest themselves in the roughness of the water/vapor interface of the film, in the irregularity of the terminating boundary of the precursor wetting film, and in the hysteretic pinning of that boundary. The roughness of the glass surface is observed to impose additional roughness to the water/vapor interface beyond that which would exist on a bulk interface. These results are discussed in terms of the disjoining pressure which governs the behavior of such films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456184
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  • 3
    Electronic Resource
    Electronic Resource
    X-ray structural studies of freely suspended ordered hydrated DMPC multimembrane films (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4519-4529 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed x-ray scattering studies of freely suspended, thick (∼2μ), oriented dimyristoyl–phosphatidyl–choline (DMPC)–water multilamellar films with the emphasis on the ordered phases. These stable films were drawn in situ on a triple axis x-ray spectrometer at a controlled, continuously variable temperature (T) and relative humidity (RH). The structure was determined at several temperatures and humidities and a T–RH phase diagram was constructed. We have found that the previously labeled ordered Lβ' phase is in fact three distinct two-dimensional phases differentiated by the direction of chain tilt with respect to the in-plane lattice. The line shapes of the scattering data indicate that a lower limit of ∼200 A(ring) may be placed on the in-plane chain–chain correlation length, while the chain positions are uncorrelated across the water layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457764
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  • 4
    Electronic Resource
    Electronic Resource
    Structure, thermodynamics, and transition kinetics of nonadecylcyclohexane (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 8225-8236 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The kinetics of crystallization in nonadecylcyclohexane, an asymmetric alkane, was studied using x-ray scattering, differential scanning calorimetry (DSC), and optical microscopy. A transient mesophase was found with a crystallization/melting temperature 13 °C below the melting point of the stable crystal phase. In a bulk sample, nucleation from the melt proceeds though the transient mesophase, which subsequently converts to the stable phase with rather slow kinetics. When quenched to low temperatures, the mesophase does not anneal and can be described as a two-dimensional (2D) Ising-like glass with regard to the up-down orientation of the asymmetric molecules. A second metastable mesomorph was also detected at low temperatures. Using an emulsified sample, homogeneous nucleation was also shown to proceed through the transient phase. The crystal structure of the transient phase is determined. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1314859
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  • 5
    Electronic Resource
    Electronic Resource
    Supercooling and transient phase induced nucleation in n-alkane solutions (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 492-500 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The supercooling exhibited by bulk solutions of the n-alkane tricosane (C23) in dodecane (C12) is measured as a function of concentration using adiabatic scanning calorimetry. For small dilutions where crystallization occurs into the rotator phase, negligible supercooling is observed. For larger dilutions where crystallization is into the herringbone crystal phase, nucleation occurs at the temperature where the rotator phase becomes stable with respect to the liquid. The supercooling in bulk n-alkane solutions is thus determined by the metastable phase diagram. This is a novel, but possibly often occurring mechanism where nucleation is induced by a transient metastable phase. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480595
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  • 6
    Electronic Resource
    Electronic Resource
    Structural effects of high pressure gas on the rotator phases of normal alkanes (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1542-1551 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effects of high pressure gases (P≤400 bar) on the RII, RI, and RV rotator phases of 21, 23, and 25 carbon normal alkanes were studied via x-ray scattering. We have measured the pressure and temperature dependence of the rotator structures and present these results in terms of the essential structural parameters: layer spacing, area per molecule, lattice distortion, and tilt. The pressure was generated by one of three gases: helium, nitrogen, or argon. In the rotator phases, argon and nitrogen intercalate between the layers while helium acts mostly as a noninteracting pressurizing medium. The thermal expansion and compressibility are anomalously large in the rotator phases, and this implies that the heat capacity in the rotator phases is dominated by anharmonic effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466633
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  • 7
    Electronic Resource
    Electronic Resource
    Phase transitions among the rotator phases of the normal alkanes (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10873-10882 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the first calorimetric study of the normal alkanes CH3–(CH2)n−2–CH3 (21≤n≤30) covering the temperature range of the five rotator phases (whose structures were previously identified using x-ray scattering) with sufficient resolution to observe the various rotator to rotator transitions. We find first-order hexagonal–orthorhombic distortion transitions; second-order azimuthal tilt-angle rotation transitions, and two types of second-order tilting transitions, one of which has the higher symmetry phase at low temperature. These transitions appear to be mean field in character, in that they are without significant pretransitional fluctuations. We discuss the calorimetric signatures for the transitions in terms of the order parameters obtained from x-ray scattering data. In addition to the transitions, we find strong temperature variation of the heat capacity in the rotator phases not associated with the transitions. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467837
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  • 8
    Electronic Resource
    Electronic Resource
    Rotator Phases in Mixtures of n-Alkanes (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 798-804 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100002a050
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  • 9
    Electronic Resource
    Electronic Resource
    The rotator phases of neat and hydrated 1-alcohols (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 7763-7773 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report an x-ray scattering study of the rotator phases in both dry and hydrated 1-alcohols CH3–(CH2)n−1–OH(12≤n≤26). Hydration was accomplished by using both fixed composition and controlled relative humidity. A hexagonal phase and two tilted phases are reported in the temperature versus chain length and temperature versus humidity phase diagrams. Hydration tends to drive the system from one tilted rotator state to the other, and then to the untilted hexagonal phase. The hexagonal phase shows a six-layer periodicity illustrating the crossover between trilayer alkane behavior and bilayer surfactant behavior. Hydration and chain-length mixing increase the temperature range of the rotator phase. The rotator phase will take in about 1 H2O per 2 alcohols which is twice the saturated water content of the liquid phase. This is shown to explain the unusual rise in the melting temperature with hydration. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472559
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  • 10
    Electronic Resource
    Electronic Resource
    Rotator phases of the normal alkanes: An x-ray scattering study (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5809-5824 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results of a detailed x-ray scattering study on the rotator phases of normal alkanes: CH3–(CH2)n−2–CH3 (20≤n≤33). We have characterized a new tilted rotator phase and determined the temperature and chain length dependence of the distortion, tilt, and azimuthal order parameters which characterize the time-space averaged structures of the five rotator phases. We have shown that there is no strong even–odd chain length effect on the phase diagram within the rotator phases and have shown the continuity of that phase diagram in the 26-27 carbon vicinity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464874
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