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  • 1995-1999  (5)
  • Boger fluid  (3)
  • eutrophication  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Shear rheology of polymer solutions near the critical condition for elastic instability (1997)
    Springer
    Rheologica acta 36 (1997), S. 97-109 
    Details
    ISSN: 1435-1528
    Keywords: Polymer migration ; anomalous theology ; Boger fluid ; normal stress ; elastic instability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The use of constant viscosity, highly elastic polymer solutions, so called Boger fluids, has been remarkably successful in elucidating the behavior of polymeric materials under flowing conditions. However, the behavior of these fluids is still complicated by many different physical processes occurring within a narrow window of observation time and applied shear rate. In this study, we investigate the long-time shear behavior of an ideal Boger fluid: a well characterized, athermal, dilute, binary solution of high molecular weight polystyrene in oligomeric polystyrene. Rheological measurements show that under an applied steady shear flow, this family of polymer solutions undergoes a transient decay of normal stresses on a timescale much longer than the polymer molecule's relaxation time. Rheological and flow visualization results demonstrate that the observed phenomenon is not caused by polymer degradation, phase separation, viscous heating, or secondary flows from elastic instabilities. Although the timescale is much shorter than that associated with polymer migration in the same solutions (MacDonald and Muller, 1996), the appearance of this phenomenon only at the rates where migration has been observed suggests that it may be a prerequisite for observing migration. In addition, we note that through sufficient preshearing of the sample, the normal stress decrease suppresses the elastic instability. These results show that there is considerable uncertainty in choosing the appropriate measure of the fluid relaxation time for consistently modeling the critical condition for the elastic instability, the decay of normal stresses, and the migration of polymer species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366816
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    A reference system for continental running waters: plant communities as bioindicators of increasing eutrophication in alkaline and acidic waters in north-east France (1996)
    Springer
    Hydrobiologia 340 (1996), S. 67-76 
    Details
    ISSN: 1573-5117
    Keywords: acidic water ; alkaline water ; autoecology ; bioindication ; macrophyte community ; eutrophication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two bioindication scales of the degree of eutrophication based on aquatic macrophyte communities were established in two types of running waters free of organic matter, the one in acidic “soft” waters (pH 5.5–7.0, conductivity 40–110 μS.cm−1), the other in alkaline hard waters (pH 7–8, conductivity 500–900 μS.cm−1). We show that the main determining factor of the macrophyte distribution is the nutrient level (trophy), especially the level of phosphate and ammonia. The acidic scale, with increasing pH, includes four stages ranging from oligotrophic to eutrophic level (traces to 300 μg.l−1 N-NHinf4p+ and P-PO4 3−), while the alkaline scale at constant pH comprises six stages of a trophic gradient. For the most part, the floristic composition found in the two sequences is different and depends on conductivity and alkalinity variation. However, some species occur in the two scales and may reflect differences in the trophic level, depending on whether the waters are alkaline or acidic. This change of trophic level for these species is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00012736
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    A macrophyte communities sequence as an indicator of eutrophication and acidification levels in weakly mineralised streams in north-eastern France (1999)
    Springer
    Hydrobiologia 410 (1999), S. 17-24 
    Details
    ISSN: 1573-5117
    Keywords: eutrophication ; acidification ; macrophyte communities ; weakly mineralized streams ; France
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Northern Vosges streams are subjected to acidification upstream and to eutrophication downstream. A bio-indicator scale of the degree of eutrophication and of the level of acidification, based on four aquatic macrophyte communities, was established in these weakly mineralized streams. Aquatic plant communities therefore begin as Group A, develop into Group B and become Group C or D downstream. The A community was characterized by bryophytes (Scapania undulata, Sphagnum sp.) and Potamogeton polygonifolius in oligotrophic, acidified to weakly acidified, and poorly buffered streams. The B community, defined by P. polygonifolius and the appearance of Ranunculus peltatus and Callitriche species (C. platycarpa, C. hamulata) was found in oligotrophic waters with a higher buffer capacity than the A community. The C community was determined by the disappearance of P. polygonifolius and the appearance of Elodea species (E. canadensis, E. nuttallii) and rare species in mesotrophic and neutral streams. The D community, with very high nutrient loading, was characterized by the abundance of Callitriche obtusangula, by the presence of Amblystegium riparium, Fissidens crassipes and the development of filamentous algae. This macrophyte sequence corresponded to an upstream to downstream zonation, which was characterized by an increase in buffer capacity and in nutrient levels and a decrease in protons and aluminium load.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003829921752
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    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Shear rheology of polymer solutions near the critical condition for elastic instability (1997)
    Springer
    Rheologica acta 36 (1997), S. 97-109 
    Details
    ISSN: 1435-1528
    Keywords: Key words Polymer migration ; anomalous rheology ; Boger fluid ; normal stress ; elastic instability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The use of constant viscosity, highly elastic polymer solutions, so called Boger fluids, has been remarkably successful in elucidating the behavior of polymeric materials under flowing conditions. However, the behavior of these fluids is still complicated by many different physical processes occurring within a narrow window of observation time and applied shear rate. In this study, we investigate the long-time shear behavior of an ideal Boger fluid: a well characterized, athermal, dilute, binary solution of high molecular weight polystyrene in oligomeric polystyrene. Rheological measurements show that under an applied steady shear flow, this family of polymer solutions undergoes a transient decay of normal stresses on a timescale much longer than the polymer molecule‘s relaxation time. Rheological and flow visualization results demonstrate that the observed phenomenon is not caused by polymer degradation, phase separation, viscous heating, or secondary flows from elastic instabilities. Although the timescale is much shorter than that associated with polymer migration in the same solutions (MacDonald and Muller, 1996), the appearance of this phenomenon only at the rates where migration has been observed suggests that it may be a prerequisite for observing migration. In addition, we note that through sufficient pre-shearing of the sample, the normal stress decrease suppresses the elastic instability. These results show that there is considerable uncertainty in choosing the appropriate measure of the fluid relaxation time for consistently modeling the critical condition for the elastic instability, the decay of normal stresses, and the migration of polymer species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366816
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Study of mixed solvent quality in a polystyrene-dioctyl phthalate-polystyrene system (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 181-192 
    Details
    ISSN: 0887-6266
    Keywords: ternary solutions ; solvent quality ; polystyrene-dioctyl phthalate ; light scattering ; Boger fluid ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polymer solvent interactions in the ternary system high molecular weight polystyrene (HMPS), low molecular weight polystyrene (LMPS), and dioctyl phthalate (DOP) have been characterized by means of intrinsic viscometry (IV), dynamic light scattering (DLS), and static light scattering (SLS). Excluded volume exponents have been extracted from the scaling of intrinsic viscosity and translational diffusivity with polymer molecular weight for a mixed solvent of 13 wt % LMPS/87 wt % DOP. The value of the excluded volume exponent, v = 0.45, indicates that HMPS in the mixed solvent DOP/LMPS has apparently assumed a reduced conformation relative to the theta condition. However, SLS measures of the second virial coefficient (A2) confirm that DOP is a theta solvent at our experimental temperature of 22°C and indicate that the addition of LMPS increases A2. SLS also suggests that neither solvent component is strongly preferentially adsorped into the HMPS coil. Our system then is a mixture of a theta solvent and a good solvent that exhibits poor solvent scaling behavior. We believe this to be the first demonstration of such behavior in a system that does not exhibit appreciable preferential adsorption. We conclude by examining our observations in the context of current descriptions of mixed solvent thermodynamics. © 1996 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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