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  • 1
    Electronic Resource
    Electronic Resource
    Response to "Comment on ‘A 250 GHz ESR study of o-terphenyl dynamic cage effects above TC' " [J. Chem. Phys. 109, 10523 (1998)] (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 10525-10526 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We address the points raised by Giordano and Leporini (GL) and show that accounting properly for the nonexponential decay of the rotational correlation function leads to improved agreement with the Stokes–Einstein–Debye (SED) relation above the crossover temperature TC for those probes 3,3′-dimethyloxazolidinyl-N-oxy-2′,3-5α-cholestane (CSL), and perdeuterated 2,2′,6,6′-tetramethyl-4-methyl aminopiperidinyl-N-oxide) (MOTA) that are well-coupled to the viscous modes of o-terphenyl (OTP) when the average relaxation rate 〈fraction SHAPE="CASE"〉16〈τ〉 is plotted versus 1/T. On the other hand, 2,2′,6,6′-tetramethyl-4-piperidine-N-oxide (PDT) shows simple Arrhenius behavior in this regime, because of weak coupling to the solvent cage, inconsistent with SED, which was clearly shown in our paper. We also suggest that the difference in chemical structure of the PDT probe, studied by us, compared to 2,2′,6,6′-tetramethylpiperidine-N-oxyl (TEMPO), studied by GL, accounts for the difference in the low-temperature relaxation behavior of the two probes. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477736
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  • 2
    Electronic Resource
    Electronic Resource
    Diffusion coefficients in anisotropic fluids by ESR imaging of concentration profiles (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3387-3395 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on the use of ESR imaging for determining the translational diffusion constants of typical ESR spin probes in ordered and isotropic solvents. A discussion is given for a Fourier deconvolution method for determining the correct concentration profile if there is more than one hyperfine line in the spectrum of the radical as well as a spatial dependence of the spectrometer sensitivity. A simple but approximate subtraction deconvolution method is also presented. The diffusion constants for 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPONE) in the nematic and isotropic phases of the liquid crystal p-pentylbenzylidine-p-butylanaline (5,4) were determined. In the isotropic phase the diffusion coefficient is isotropic (D=2.5×10−6 cm2 s−1, at 50 °C), while in the nematic phase it was found to be mildly anisotropic. The diffusion coefficients for motion perpendicular and parallel to the director axis in the nematic phase are respectively, D⊥ =9.0×10−7 cm2 s−1, D(parallel) =6.4×10−7 cm2 s−1 at 27 °C. This is interpreted in terms of some smectic-like character in the nematic phase of 5,4. Possible improvements in the technique are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450221
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  • 3
    Electronic Resource
    Electronic Resource
    Rigid-backbone polymers. Dielectric relaxation of isotropic and lyotropic solutions of poly(n-hexylisocyanate) (1982)
    s.l. : American Chemical Society
    Macromolecules 15 (1982), S. 642-651 
    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/ma00230a084
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  • 4
    Electronic Resource
    Electronic Resource
    Concentrated solutions of polydisperse rodlike polymers in the isotropic and lyotropic liquid-crystalline phases. I. The effects of molecular length distribution on phase behavior (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 21 (1983), S. 197-212 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The earlier calculations of Moscicki and Williams of the phase behavior of rodlike macromolecules in solution incorporating a Gaussian distribution of rod lengths have been extended to include, in addition to a “basic” Gaussian distribution, a small amount of high-molecular-weight species which are characterized by a δ-function or “box-function” distribution. It is shown that C*p, the concentration of polymer at which the biphasic material (isotropic plus anisotropic phase) first appears may be substantially lowered in comparison with that for the system comprising only the basic distribution. The volume fraction ΦA of anisotropic phase, the compositions of the two phases, and the distribution of species between the phases are calculated for a range of polymer concentration which spans the isotropic, biphasic, and anisotropic phase and, among several features obtained, it is shown that the high-molecular-weight species are essentially responsible for the initial formation of anisotropic phase in the biphasic system. The results of the calculations have important implications for the interpretation of published dielectric relaxation data for polyalkylisocyanates in solution at high concentration and for published shear-flow viscosity data for polyalkylisocyanates and poly(p-benzamide) in solution at high concentration and these are discussed in some detail.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1983.180210203
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  • 5
    Electronic Resource
    Electronic Resource
    Concentrated solutions of polydisperse rodlike polymers in the isotropic and lyotropic liquid-crystalline phases. II. Model simulation of the dielectric relaxation behavior of poly(n-alkylisocyanates) in toluene and comparison with experimental results (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 21 (1983), S. 213-231 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A simulation has been made of the dielectric relaxation behavior of poly(n-hexylisocyanate) in solution covering the isotropic, biphasic, and anisotropic ranges. The simulation incorporates the Flory-Abe statistical mechanical theory for the phase behavior of rodlike macromolecules in solution and the Warchol, Vaughan, Wang, and Pecora theory for the dynamics of a rodlike molecule in a virtual cone prescribed by the neighboring molecules. It is shown that asymmetric Gaussian, Gaussian, or Poisson distributions of molecular weight do not lead to dielectric behavior of the type observed experimentally by Moscicki, Williams, and Aharoni but addition of a high-molecular-weight “tail” to such distributions and taking account of the dependence of relaxation time on molecular length gives a simulation of the dielectric increment Δε, the loss maximum ε″m, and frequency of maximum loss fm, which vary with polymer concentration in a manner entirely consistent with the experimental data.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1983.180210204
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  • 6
    Electronic Resource
    Electronic Resource
    Numerical study of the phase behavior of rods in solution: Warner-Flory model with polydisperse system of rodsThis work was carried out while the author was with the Université de Nancy I, Laboratoire de Chimie Théorique, Vandoeuvre-les-Nancy, and the Laboratoire de Recherches sur les Interactions Gaz-Solides, Villers-les-Nancy, France. (1985)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 23 (1985), S. 327-341 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Phase equilibria of polydisperse rods in solution are studied in terms of the Warner-Flory model. Numerical calculations are made with a Gaussian-like asymmetric distribution of rod lengths. The aim of these studies is to investigate (i) the dependence of the phase diagram on the shape of the polydispersity distribution function and (ii) the isotropic-anisotropic phase separation within the coexistence range. It is shown that, as a consequence of polydispersity, even for a narrow distribution, the phase diagram is very simple, with only one type of anisotropic phase present. However, within the biphasic range, the properties of the anisotropic phase vary significantly with temperature. At high temperatures, they are essentially governed by steric effects and at low temperatures by both steric effects and soft anisotropic interactions between the rods.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1985.180230208
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