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  • 1
    Electronic Resource
    Electronic Resource
    Nuclear magnetic resonance studies of diamagnetic metal-diethylenetriaminepentaacetate complexes (1979)
    s.l. : American Chemical Society
    Inorganic chemistry 18 (1979), S. 1330-1332 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic50195a033
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  • 2
    Electronic Resource
    Electronic Resource
    Structure-activity relationships in the dodecapeptide .alpha. factor of Saccharomyces cerevisiae (1983)
    s.l. : American Chemical Society
    Biochemistry 22 (1983), S. 1298-1304 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00274a047
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  • 3
    Electronic Resource
    Electronic Resource
    Nitrogen fertilizers promote denitrification (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 211-220 
    Details
    ISSN: 1432-0789
    Keywords: Key words Denitrification ; Fertilizer efficiency ; 15N ; Labelled dinitrogen ; Nitrification ; Nitrous oxide ; Urea ; Waterlogged soil ; Water-soluble organic carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A laboratory study was conducted to compare the effects of different N fertilizers on emission of N2 and N2O during denitrification of NO3 – in waterlogged soil. Field-moist samples of Drummer silty clay loam soil (fine-silty, mixed, mesic Typic Haplaquoll) were incubated under aerobic conditions for 0, 2, 4, 7, 14, 21, or 42 days with or without addition of unlabelled (NH4)2SO4, urea, NH4H2PO4, (NH4)2HPO4, NH4NO3 (200 or 1000 mg N kg–1 soil), or liquid anhydrous NH3 (1000 mg N kg–1 soil). The incubated soil samples were then treated with 15N-labelled KNO3 (250 mg N kg–1 soil, 73.7 atom% 15N), and incubation was carried out under waterlogged conditions for 5 days, followed by collection of atmospheric samples for 15N analyses to determine labelled N2 and N2O. Compared to samples incubated without addition of unlabelled N, all of the fertilizers promoted denitrification of 15NO3 –. Emission of labelled N2 and N2O decreased in the order: Anhydrous NH3〉urea〈$〉\gg〈$〉 (NH4)2HPO4〉(NH4)2SO4≃NH4NO3≃NH4H2PO4. The highest emissions observed with anhydrous NH3 or urea coincided with the presence of NO2 –, and 15N analyses indicated that these emissions originated from NO2 – rather than NO3 –. Emissions of labelled N2 and N2O were significantly correlated with fertilizer effects on soil pH and water-soluble organic C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050233
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  • 4
    Electronic Resource
    Electronic Resource
    Theory and simulation of the swelling of polymer gels (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 404-418 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A combined discontinuous molecular dynamics and Monte Carlo simulation technique is used to study the swelling of athermal, continuous-space, near-perfect, trifunctional polymer networks containing hard chains of lengths 20 and 35 immersed in an athermal hard-sphere solvent. The swelling simulations are conducted under conditions of constant pressure and chemical potential. A simple, analytical theory for gel swelling is presented in which the gel free energy is calculated as the sum of an elastic, affine-type term, and a liquidlike mixing term that is based on the generalized-Flory dimer equation of state. The theory shows good agreement with our simulation results for the gel properties at swelling equilibrium. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481806
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  • 5
    Electronic Resource
    Electronic Resource
    Pressure–volume properties of endlinked hard-chain polymer networks (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7556-7573 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Equilibrium molecular dynamics simulations are used to obtain the pressure and configurational chain properties of near-perfect, off-lattice, trifunctional hard-chain networks of chain lengths 20, 35, 50, and 100, and of tetrafunctional hard-chain networks of chain lengths 20, 35, and 50 over a range of packing fractions. Our simulation results show that the variation of network pressure with density is similar to that of uncrosslinked chain systems of the same chain length, except at low densities where the network pressure shows a negative region, as first observed by Escobedo and de Pablo. We present a theoretical treatment leading to an analytical expression for the network pressure as the sum of liquid-like and elastic contributions. The liquid-like contribution is obtained by extending the generalized Flory-dimer theory to networks, and the elastic contribution is obtained by treating the network as a set of interpenetrated dendrimers and using an ideal chain-spring analogy to calculate the free energy. The theoretical predictions for network pressure are in good agreement with simulation data. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478659
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  • 6
    Electronic Resource
    Electronic Resource
    Electrokinetic studies on ion-exchange membranes. 5. Streaming potentials (1977)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 81 (1977), S. 2114-2118 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100537a015
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  • 7
    Electronic Resource
    Electronic Resource
    Salting-in behavior of isotropic and anisotropic aqueous hydroxypropylcellulose solutions (1997)
    Springer
    Colloid & polymer science 275 (1997), S. 284-287 
    Details
    ISSN: 1435-1536
    Keywords: Key words Salting-in ; hydroxypropylcellulose ; rheology ; chiral nematic mesophase ; liquid crystal
    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  Salts with large polarizable ions are capable of salting-in complex aqueous polymer solutions exhibiting microstructure, thereby inducing changes in the phase behavior and properties of the solutions. In this work, the dynamic rheological properties of isotropic and mesomor-phic hydroxypropylcellulose (HPC) in aqueous media have been investigated in the presence of one such salt, guanidine thiocyanate (GuSCN). Addition of this salt to isotropic aqueous HPC solutions is found to induce an increase in the magnitude of the elastic shear modulus (G′). At HPC concentrations above the isotropic→mesophase transition, however, addition of GuSCN results in a substantial reduction in G′ due to microstructural changes in the chiral nematic HPC mesophase. This reduction in G′ indicates that the microstructure of a water-soluble polymer exhibiting supramolecular organization can be tailored through salting-in, and is likewise expected to facilitate the commercial processing of HPC at high solids concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050082
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  • 8
    Electronic Resource
    Electronic Resource
    Comparison of the rheology of polymer melts in shear, and biaxial and uniaxial extensions (1987)
    Springer
    Rheologica acta 26 (1987), S. 144-151 
    Details
    ISSN: 1435-1528
    Keywords: Extensional deformation ; polymer melt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The experimental properties of different polymer melts, polystyrene, high density polyethylene and low density polyethylene are compared for the first time in three different deformations: step shear, step biaxial extension and steady uniaxial extension. Properties of three other melts are also studied in step biaxial and shear experiments. For our comparative purposes some data of Laun and Winter from the literature are used, as well as new data reported here. In all the step strain experiments, the stresses can be factored into a time dependent relaxation modulus and a strain dependent damping function. The data are interpreted using a differential constitutive equation of Larson which satisfies this time-strain separability and has a single parameter that describes the strain softening character of the material. Results show that differences in the properties of the melts are most pronounced in uniaxial extension and least in biaxial extension. All melts follow the Doi-Edwards prediction relatively closely in biaxial extension. In uniaxial extension, the branched material shows a strong strain hardening effect although its shear and biaxial properties are similar to the other melts. The constitutive model gives a reasonably good fit to the data in all three deformations for unbranched materials for the same value of the adjustable parameter; the model, however, fails for the branched low density polyethylene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01331972
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  • 9
    Electronic Resource
    Electronic Resource
    In situ technique for monitoring the gelation of UV curable polymers (1992)
    Springer
    Rheologica acta 31 (1992), S. 151-160 
    Details
    ISSN: 1435-1528
    Keywords: Radiation cross-link ; ultraviolet radiation ; gelation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Ultraviolet-radiation-cured cross-linked systems are used extensively in optoelectronic applications. We describe a new in situ technique for doing controlled curing of photosensitive materials and monitoring the gelation through dynamic theological measurements. In this method, a sample placed between quartz windows of a modified parallel plate fixture of a Rheometrics Mechanical Spectrometer is radiated from a collimated UV source using a liquid light guide and a mirror. By varying the sample exposure to UV radiation, the degree of cross-linking can be precisely controlled to observe the material behavior in the pre, post, and critical gel state. Time-dependent measurements on urethane based materials show the gelation behavior to have an “induction” period with no change in dynamic moduli (G′, G″), followed by their sharp increase as the materials develop a network structure. The critical gel point is characterized by a power-law dependence of the dynamic moduli on frequency. The gelation kinetics scales with sample thickness and radiation intensity, the scaling factor in both cases being the critical gelation time. The rheological measurements correlate with differential photocalorimetric studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00373237
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  • 10
    Electronic Resource
    Electronic Resource
    Step planar extension of polymer melts using a lubricated channel (1991)
    Springer
    Rheologica acta 30 (1991), S. 1-6 
    Details
    ISSN: 1435-1528
    Keywords: Extension ; step strain ; polyethylene ; lubrication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A technique to do step planar extension on polymer melts has been developed using a rectangular channel with lubricated walls and the linear motor of the Rheometrics System Four rheometer. Using this method we probe the stress relaxation of two polymer melts, a linear low density polyethylene (LLDPE) and a highly branched low density polyethylene (IUPAC X), and compare the step planar extensional data to step shear data. Since a step planar deformation is theoretically equivalent to a step shear in a rotating frame of reference, we expect that the nonlinear modulus for step planar extension should be equivalent to that for step shear. Although we find the time dependence of the stress relaxation modulus to be the same in both shear and planar extension, the strain dependence is surprisingly different for the two experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366788
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