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  • 1
    Electronic Resource
    Electronic Resource
    The Role of Lithium Salts in the Conductivity and Phase Morphology of a Thermoplastic Polyurethane (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 4268-4277 
    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/ma00116a030
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  • 2
    Electronic Resource
    Electronic Resource
    Conductivity and Morphological Studies of TPU-NH4CF3SO3 Polymeric Electrolytes (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 15142-15152 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100041a034
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  • 3
    Electronic Resource
    Electronic Resource
    Dynamics of the hydrogen and phosphate ions in proton conducting gel/D3PO4 electrolytes: A 2H and 31P nuclear magnetic resonance study (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7474-7482 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Protonic conducting polymeric gel synthesis is motivated by its possible application in various electrochemical devices. This study focuses on the molecular motion of deuterons in gels formed with D3PO4 dissolved in propylene carbonate and a polymer matrix obtained using a free radical polymerization of methyl methacrylate with a cross-linking agent triethylene glycol dimethacrylate. Results are reported for samples containing 11, 23, and 45 mass % D3PO4. The measurements of the diffusion coefficients for deuterons and 31P show conclusively that the deuterons diffuse faster than the phosphorus carrying species. Therefore, the ionic conductivity results from a combination of the vehicular and Grotthus-type mechanisms. Species such as D2PO4−, D3PO4, or D4PO4+ are formed and the motion of the ions represents the vehicular mechanism while deuteron hopping from one species to the others constitutes the Grotthus mechanism. The nuclear magnetic resonance (NMR) spectra are consistent with the deuterons residing in a narrow distribution of sites; activation energies are similar for all samples, indicating that the barrier height to motion is independent of the concentration of D3PO4. This information reinforces the picture that the deuterons are always closely associated with PO4 groups. The correlation times determined from the deuteron nuclear relaxation times do not follow the Vogel–Tamman–Fulcher behavior observed in the conductivity measurements. The temperature dependence of the conductivity follows that of the structural relaxation or α process for T〉1.2Tg, while the NMR correlation time is determined by any motion which modulates the electric field gradient at the deuteron site. Both the α and slow β processes influence the NMR correlation times. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478650
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamics of sodium ions in NaClO4 complexed in poly(propylene-oxide): A 23Na nuclear magnetic resonance study (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3360-3372 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Amorphous poly(propylene oxide), PPO (molecular weights, 425 and ∼106), complexed with NaClO4 salt has ionic conductivities as high as 10−5 S/cm at room temperature. In an attempt to directly study the dynamics of the Na+ ions, (I=3/2) nuclear magnetic resonance (NMR) spin-lattice relaxation times, T1, and spin–spin relaxation times, T2, at a resonance frequency of 77.0 MHz have been measured over the temperature range from 150 to 390 K. A range of salt compositions [(PPO)nNaClO4; n=8–30] have been investigated. In addition, the glass transition temperature for each sample is reported. The recovery of equilibrium magnetization following a π/2 pulse is biexponential as expected for a spin I=3/2 system in the viscous liquid region. Below Tg a better fit to the magnetization recovery curve can be obtained if Kohlrausch–Williams–Watts (KWW) functions are used in place of the exponential functions. At low temperature the molecular motion has slowed to the point where a common spin temperature is not achieved by ionic diffusion. Two T2 values are observed over a limited temperature region near the T1 minimum. In the remaining low temperature region only the T2 associated with the central transition could be determined because the large 23Na quadrupole coupling constant made detection of the satellite transitions impossible. There is no evidence from the NMR relaxation time data for two Na+ populations. The experimental spin-lattice relaxation times can be analyzed to determine the correlation time for the ionic motion as a function of reciprocal temperature. The correlation time data display a distinct change in behavior at Tg which is interpreted as an indication of a crossover between two ionic transport mechanisms. Plots of T1 as a function of Tg/T indicate that dynamics for T〉Tg are largely determined by the flexibility of the polymer host (the α process) whereas a different process dominates for T〉Tg (presumably the β process). A comparison of correlation times derived from NMR relaxation times and ionic conductivities show a marked difference especially in the region of Tg. The conductivity decreases rapidly while the sodium ion motion continues with a correlation time ∼10−6 s through the glass transition. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475735
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  • 5
    Electronic Resource
    Electronic Resource
    Genetic heterogeneity in the Trypanosoma brucei gambiense genome analysed by random amplification of polymorphic DNA (1996)
    Springer
    Parasitology research 82 (1996), S. 535-541 
    Details
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract   The random amplification of polymorphic DNA (RAPD) technique has the potential to produce large amounts of characterisation data very quickly and simply, using far less DNA than conventional restriction-fragment-length polymorphism (RFLP) analysis. In the present study we assessed genetic heterogeneity among 34 Trypanosoma brucei gambiense isolates from various endemic areas in Africa by the RAPD technique using 8 arbitrary primers and compared the results with those obtained previously from RFLP analysis of polymorphisms in 5 variant surface glycoprotein (VSG) genes. The isolates were compared both among themselves and with 3 T. b. non-gambiense isolates. Most of the primers produced RAPD profiles specific for T. b. gambiense, with 4 primers showing marked polymorphisms between T. b. gambiense and non-gambiense stocks. These primers also showed minor variations between the T. b. gambiense stocks, and 2 revealed differences between Cameroonian stocks. These results were comparable with those produced by RFLP analysis, where certain polymorphisms are characteristic of T. b. gambiense. Numerical analysis showed a high correlation between the RAPD and RFLP data, with genetic variation being detected at a finer level by RAPD analysis. We conclude that RAPD analysis provides a simple and accurate method for the characterisation of T. b. gambiense.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004360050158
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  • 6
    Electronic Resource
    Electronic Resource
    Ionic conduction in composite polymer electrolytes at subambient temperatures (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2911-2917 
    Details
    ISSN: 0887-6266
    Keywords: composite polymer electrolytes ; conduction mechanism ; glass transition temperature ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The majority of investigations carried out on polymer(SINGLEBOND) salt systems have been on polyether electrolytes at moderate temperatures where such electrolytes exhibit macroscopic uniformity. Relatively little attention has been paid to the subambient temperature region where composite electrolytes based on polyethers exhibit much higher conductivities than their pure polyether electrolyte analogues. For all of the composite systems studied the conduction mechanism changes from one in which the ions are coupled to the polymer segmental relaxations to one in which the ions are decoupled and thermally activated ionic hopping produces higher conductivities than would be expected from ion-segmental coupling and higher than observed for the base polyether(SINGLEBOND) salt system. This change has been observed at temperatures between 10 and 80°C above the respective glass transition temperatures. The relationship between this interaction and these higher conductivities at subambient temperatures is explored and discussed. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Phase separation morphology of thin films of polystyrene/polyisoprene blends (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 3017-3024 
    Details
    ISSN: 0887-6266
    Keywords: phase separation morphology ; thin films ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We present the results of a study of the morphology of phase separation in a thin film blend of polystyrene (PS) and polyisoprene (PI) in a common solvent of toluene. The blend is quenched by rapid solvent evaporation using a spincoating technique rather than a temperature quench. The mass fraction of polystyrene is varied to determine the effect of the substrate on thin film phase separation morphology. We compare the phase separation morphology for very thin films of the PS/PI blend cast onto three different substrates: Si(001) with a native oxide layer (Si (SINGLEBOND) SiOx), Si(001) etched in hydrofluoric acid (Si-H), and a Au/Pd alloy sputtered onto Si(001). We observe large differences between the morphologies of 1000 Å thick blend films on the Si(SINGLEBOND) SiOx and Si-H substrates as the mass fraction is varied due to the difference in the wetting properties of PS on the two substrates. Smaller differences are observed between the films on the Si(SINGLEBOND) SiOx and Au/Pd substrates only for film thicknesses h 〈 600 Å. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Photon correlation spectroscopy of bulk poly(n-hexyl methacrylate) near the glass transition (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2291-2305 
    Details
    ISSN: 0887-6266
    Keywords: glass transition ; polymer dynamics ; photon correlation spectroscopy ; dynamic heterogeneities ; longitudinal density fluctuations ; poly(n-hexyl methacylate) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Slowly relaxing longitudinal density fluctuations in an optically perfect sample of bulk poly(n-hexyl methacrylate) (PHMA) have been studied by photon correlation spectroscopy in the temperature range 10-36°C. The glass transition temperature for this sample was measured to be Tg = -3°C by differential scanning calorimetry. The optical purity of the sample was verified by Rayleigh-Brillouin spectroscopy and the Landau-Placzek ratio was observed to be 2.3 at 25°C. Light-scattering relaxation functions were obtained over the time range 10-6-1 s. The shape of the relaxation functions broadened as the temperature was lowered towards the glass transition. Quantitative analysis of the results was carried out using the Kohlrausch-Williams-Watts (KWW) function to obtain average relaxation times, 〈τ〉, and width parameters, β. The width parameter decreased from 0.43 to 0.21 over the temperature interval, as suggested by visual inspection. Average relaxation times shifted with temperature in a manner consistent with previous mechanical studies of the primary glass-rubber relaxation in PHMA. The relaxation functions were also analyzed in terms of a distribution of relaxation rates, G(Γ). The calculated distributions were unimodal at all temperatures. The average relaxation times obtained from G(Γ) were in agreement with the KWW analysis, and the shape of the distribution broadened as the sample was cooled. The rate at which G(Γ) displayed a maximum correlated well with the corresponding frequency of maximum dielectric loss for PHMA. The temperature dependence of these two quantities could be reproduced with an Arrhenius activation energy of 21 Kcal/mol. A consistent picture of the molecular dynamics of PHMA near the glass transition requires a strong secondary relaxation process with a different temperature dependence from the primary glass-rubber relaxation. The present results suggest that the behavior of PHMA is similar to the other poly(alkyl methacrylates). © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Brillouin light scattering studies of the mechanical properties of polystyrene/polyisoprene multilayered thin films (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 3009-3016 
    Details
    ISSN: 0887-6266
    Keywords: polymer multilayered films ; mechanical properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have used Brillouin light scattering (BLS) to investigate the mechanical properties of thin polystyrene (PS) and polyisoprene (PI) films incorporated in a multilayer geometry consisting of alternating layers of the two polymers. All samples had a total thickness h ∼ 1600 Å, and consisted of between 2 and 10 individual polymer films; individual layer thicknesses were as small as 160 Å. Ellipsometry was used to determine the thickness of the PS and PI layers. The velocities of several high-frequency film-guided mechanical waves were measured using BLS and the results are compared with values calculated using an effective medium approach. The effective elastic constants of the multilayered films were obtained from those determined for thick films of PS and PI. Remarkable agreement was obtained between the measured and calculated velocities even for samples in which the individual layer thicknesses were much less than the unperturbed size of the polymer molecules. These results suggest that the mechanical properties of polymers change very little even when the molecules are forced into highly confined geometries. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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