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  • 1
    Electronic Resource
    Electronic Resource
    Effects of concentrated matrices on the determination of trace levels of platinum and gold in aqueous samples using solvent extraction-Zeeman effect graphite furnace atomic absorption spectrometry and inductively coupled plasma-mass spectrometry
    Amsterdam : Elsevier
    Analytica Chimica Acta 229 (1990), S. 227-238 
    Details
    ISSN: 0003-2670
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/S0003-2670(00)85133-8
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  • 2
    Electronic Resource
    Electronic Resource
    Order–disorder transition and ordering kinetics in binary diblock copolymer mixtures of styrene and isoprene (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2083-2088 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The order–disorder transition (ODT) and the ordering kinetics have been studied in two symmetric diblock copolymers of styrene and isoprene and their binary mixtures with rheology. The binary mixtures formed a single microdomain (with lamellar morphology) composed of short and long chains as confirmed by small angle x-ray scattering (SAXS). The order–disorder transition temperature (TODT), obtained from the discontinuity in the storage modulus G′, varies linearly with the number average degree of polymerization. For shallow quenches, the ordering kinetics proceed via nucleation and growth. The characteristic time of this process scales with N¯−1/3, where N¯ is the Ginzburg parameter, in agreement with the theoretical predictions [G. H. Fredrickson and K. Binder, J. Chem. Phys. 91, 7265 (1989)]. Our results indicate that the ordering kinetics of symmetric diblock copolymers near the ODT are fluctuation controlled. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470965
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  • 3
    Electronic Resource
    Electronic Resource
    Segmental dynamics and incompatibility in hard/soft polymer blends (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 5997-6005 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on the segmental dynamics of the binary polymer blend polystyrene (PS)/poly (methylphenylsiloxane) (PMPS) in the two-phase region using dielectric spectroscopy that essentially probes the PMPS component. Based on the experimental orientation relaxation functions, the average glass transition temperature Tg controls phase separation. When the spinodal temperature Ts exceeds Tg, the PMPS segmental relaxation displays two distinct decays characteristic of a merely pure and a mixed, roughly at the initial composition, PMPS regions. On the contrary, when Ts falls in the proximity of Tg, the PMPS relaxation is strongly nonexponential and its average time reflects mixed regions rich in PMPS due to incomplete phase separation, which drives only the glassy phase out of local thermodynamic equilibrium. Distinct morphological differences in the two-phase state of these blends, inferred from their segmental dynamics, are revealed by transmission electron microscopy. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476012
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  • 4
    Electronic Resource
    Electronic Resource
    Coupling of concentration fluctuations to viscoelasticity in highly concentrated polymer solutions (1996)
    Springer
    Colloid & polymer science 274 (1996), S. 1033-1043 
    Details
    ISSN: 1435-1536
    Keywords: Polymers ; concentrated solutions ; entanglements ; dynamics ; photon correlation spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Photon correlation spectroscopy in the polarized geometry has been used to systematically investigate the complex dynamics of a highly concentrated entangled polymer solution in a nominally good solvent, poly(butylacrylate) in dioxane. In addition to the well known fast cooperative diffusion process, a slow virtuallyq-independent mode is detected, whereq is the scattering wavevector, in agreement with previous experimental works on semidilute solutions. This mode is attributed to the viscoelastic nature of the transient physical network, formed by the entanglements, which relaxes its elastic stress induced by the concentration fluctuations, as confirmed by small amplitude oscillatory shear measurements; the latter reveal a terminal relaxation time comparable to the characteristic time of the slow relaxation process. Results, especially in terms of concentration and temperature dependence, are evaluated and discussed in view of the existing theoretical treatments in the field, predicting the existence of the slow viscoelastic relaxation. The relationship between dynamic light scattering and mechanical spectroscopy is established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00658368
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  • 5
    Electronic Resource
    Electronic Resource
    The potential for free and mixed convection in sedimentary basins (1999)
    Springer
    Hydrogeology journal 7 (1999), S. 505-520 
    Details
    ISSN: 1435-0157
    Keywords: Key words numerical modeling ; free convection ; general hydrogeology ; sedimentary rocks ; thermal conditions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Résumé La convection thermale libre et la convection mixte sont considérées comme les mécanismes potentiels de transport de matière et de chaleur dans les bassins sédimentaires. La convection mixte se produit lorsque des écoulements horizontaux (convection forcée) se surimposent à des écoulements commandés par les températures. En section transversale, la convection mixte est caracterisée par des cellules de convection qui se déplacent latéralement dans la direction de l'écoulement convectif forcé. Des simulations 2D par éléments finis de l'écoulement d'eaux souterraines de densités variables et du transport de chaleur dans une couche poreuse horizontale ont été réalisées afin de déterminer les valeurs moyennes critiques du nombre de Rayleigh dans le cas de la convection libre, en utilisant des limites à la fois isothermes et semi-perméables. Des simulations supplémentaires ont imposé un flux latéral variable de fluide sur un fonctionnement d'ensemble en convection libre. Les résultats de ces expériences indiquent que la convection forcée devient prédominante, éliminant complètement l'écoulement commandé par les différences de densité, lorsque le flux total de fluide soumis à la convection forcée devient supérieur au flux total possible dûà la convection libre. Les calculs d'indice d'altération thermal de la roche (RAI=qT) définissent les grandes lignes de la diagenèse potentielle produite par les mouvements du fluide sous l'effet des gradients de température. La convection libre produit une distribution particulière de valeurs de RAI alternativement positives et négatives, alors que la convection mixte produit une simple succession de couches positives et négatives, et en général une moindre altération diagénétique.
    Notes: Abstract  Free thermal convection and mixed convection are considered as potential mechanisms for mass and heat transport in sedimentary basins. Mixed convection occurs when horizontal flows (forced convection) are superimposed on thermally driven flows. In cross section, mixed convection is characterized by convection cells that migrate laterally in the direction of forced convective flow. Two-dimensional finite-element simulations of variable-density groundwater flow and heat transport in a horizontal porous layer were performed to determine critical mean Rayleigh numbers for the onset of free convection, using both isothermal and semi-conductive boundaries. Additional simulations imposed a varying lateral fluid flux on the free-convection pattern. Results from these experiments indicate that forced convection becomes dominant, completely eliminating buoyancy-driven circulation, when the total forced-convection fluid flux exceeds the total flux possible due to free convection. Calculations of the thermal rock alteration index (RAI=q·∇T) delineate the patterns of potential diagenesis produced by fluid movement through temperature gradients. Free convection produces a distinct pattern of alternating positive and negative RAIs, whereas mixed convection produces a simpler layering of positive and negative values and in general less diagenetic alteration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100400050224
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  • 6
    Electronic Resource
    Electronic Resource
    LDA measurements of steady streaming flows of Newtonian and viscoelastic fluids (1995)
    Springer
    Experiments in fluids 20 (1995), S. 21-28 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract LDA experiments have been conducted in a two-dimensional steady streaming flow field in order to determine the secondary velocity profiles. We describe here an LDA system developed to resolve small secondary-flow velocities and to detect flow reversals due to viscoelasticity. Results compare well with theoretical predictions. A detailed analysis of the errors and uncertainties involved in the measurements confirms the reliability and reproducibility of the measurements. Although the method has been applied here to a specific flow field, the technique should be applicable to a number of secondary flows, such as those which can occur in curved pipes and in oscillating pipe flows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00190594
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  • 7
    Electronic Resource
    Electronic Resource
    Gelation kinetics in elastomer/thermoset polymer blends (1998)
    Springer
    Rheologica acta 37 (1998), S. 614-623 
    Details
    ISSN: 1435-1528
    Keywords: Key words Gelation ; curing ; epoxy/rubber ; rheology ; blends
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The chemical gelation of polymer blends involving a thermoset component has been investigated utilizing multiple waveform dynamic rheology, complemented by differential scanning calorimetry and small angle x-ray scattering measurements. Three epoxy/rubber mixtures, with different degrees of pre-reacted material and catalyst, were used. The curing temperatures were determined with simple temperature ramps, whereas the characteristic gel times were quantified using the well-known self-similarity of the gel structure, which yielded a very low gel exponent (0.05), indicative of the high molecular weights and additives used in the samples; this exponent was unchanged with temperature, suggesting the same gelation mechanism. These times decreased with increasing temperature. Gelation was not affecting the phase-separated morphology. The presence of pre-reacted material and catalyst were found to reduce the gel times (for different temperature steps). Finally, the shear history of the samples did not affet the curing temperatures and kinetics. These results can serve as a useful guide for appropriately blending thermosetting and thermoplastic compounds in order to obtain structural materials for different applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050148
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