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  • Articles  (18)
  • viscoelasticity  (18)
  • Springer  (18)
  • Nature Publishing Group
  • 1995-1999  (18)
  • 1960-1964
  • 1945-1949
  • 1997  (18)
  • Chemistry and Pharmacology  (18)
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  • Articles  (18)
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  • Springer  (18)
  • Nature Publishing Group
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  • 1995-1999  (18)
  • 1960-1964
  • 1945-1949
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  • 1
    Electronic Resource
    Electronic Resource
    Strain hardening of fibrin gels and plasma clots (1997)
    Springer
    Rheologica acta 36 (1997), S. 262-268 
    Details
    ISSN: 1435-1528
    Keywords: Fibrin ; viscoelasticity ; strain hardening ; clot retraction ; platelets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Biological macromolecules have unique rheological properties that distinguish them from common synthetic polymers. Among these, fibrin has been studied extensively to understand the basic mechanisms of viscoelasticity as well as molecular mechanisms of coagulation disorders. One aspect of fibrin gel rheology that is not observed in most polymeric systems is strain hardening: an increase in shear modulus at strain amplitudes above 10%. Fibrin clots and plasma clots devoid of platelets exhibit shear moduli at strains of approximately 50% that are as much as 20 times the moduli at small strains. The strain hardening of fibrin gels was eliminated by the addition of platelets, which caused a large increase in shear storage modulus in the low strain linear viscoelastic limit. The reduction in strain hardening may result from fibrin strand retraction which occurs when platelets become activated. This interpretation is in agreement with recent theoretical treatments of semi-flexible polymer network viscoelasticity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366667
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  • 2
    Electronic Resource
    Electronic Resource
    Thermodynamic and transport properties of viscoelastic and gel-like solutions in micellar solutions: Water+CTAB +phenol (1997)
    Springer
    Colloid & polymer science 105 (1997), S. 326-331 
    Details
    ISSN: 1435-1536
    Keywords: Cationic surfactant ; phenol ; viscoelasticity ; thermodynamic properties ; transport properties
    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 The study of micellar systems water + CTAB + phenol, as function of the concentration of the solutes and of the temperature, was realised by calorimetry, conductometry and rheology. These different techniques have allowed to characterise the formation of complexes. The presence of phenol located between head groups of the surfactant diminishes the repulsive forces existing between the cationic groups, favoring the formation of worm-like micelles. The entanglement of these micelles provides viscoelasticity with the increase of phenol concentration and solutions seem to be gelled when ratioR=[phenol]/ [CTAB] is close to 1/1, similar to the behavior of solutions of polymers. For larger ratioR, or at elevated temperature, solutions become fluid again, indicating the weakness of the worm-like micelles comparatively to polymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188973
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  • 3
    Electronic Resource
    Electronic Resource
    Interaction of Formic Acid with the Silica Gel Network (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 165-171 
    Details
    ISSN: 1573-4846
    Keywords: aging ; syneresis ; shrinkage ; formic acid ; viscoelasticity ; permeability ; pore size ; modulus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Silica gels can be made by direct reaction of formic acid with tetraethyl orthosilicate. We have characterized wet gels of this type using a beam-bending technique that yields the elastic modulus, Poisson's ratio, viscoelastic relaxation function, and permeability. When the experiment is performed in ethyl formate, the silica network behaves in an elastic fashion; the permeability is low (〈1 nm2), indicating a pore radius of 〈4.3 nm. The capillary pressure generated in such small pores is estimated to be sufficient to cause collapse of the pores during drying, which would account for the observed ultramicropores in this type of gel. When the pore liquid contains formic acid, viscoelastic relaxation is relatively rapid. Studies of cyclosiloxane compounds indicate that formic acid can attack only the strained siloxane bonds of the network, which would account for the relaxation behavior. Aging in formic acid causes rapid initial shrinkage, because formic acid accelerates condensation of silanols, which drives syneresis; the modulus increases and the permeability decreases monotonically, so there is no indication of coarsening during aging in formic acid, even at 70°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026464918986
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  • 4
    Electronic Resource
    Electronic Resource
    Interaction of formic acid with the silica gel network (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 165-171 
    Details
    ISSN: 1573-4846
    Keywords: aging ; syneresis ; shrinkage ; formic acid ; viscoelasticity ; permeability ; pore size ; modulus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Silica gels can be made by direct reaction of formic acid with tetraethyl orthosilicate. We have characterized wet gels of this type using a beam-bending technique that yields the elastic modulus, Poisson’s ratio, viscoelastic relaxation function, and permeability. When the experiment is performed in ethyl formate, the silica network behaves in an elastic fashion; the permeability is low (〈1 nm2), indicating a pore radius of 〈4.3 nm. The capillary pressure generated in such small pores is estimated to be sufficient to cause collapse of the pores during drying, which would account for the observed ultramicropores in this type of gel. When the pore liquid contains formic acid, viscoelastic relaxation is relatively rapid. Studies of cyclosiloxane compounds indicate that formic acid can attack only the strained siloxane bonds of the network, which would account for the relaxation behavior. Aging in formic acid causes rapid initial shrinkage, because formic acid accelerates condensation of silanols, which drives syneresis; the modulus increases and the permeability decreases monotonically, so there is no indication of coarsening during aging in formic acid, even at 70°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02436835
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of Compaction Temperature on Consolidation of Amorphous Copolymers with Different Glass Transition Temperatures (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 415-419 
    Details
    ISSN: 1573-904X
    Keywords: tablet ; copolymer ; glass transition temperature ; porosity ; viscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The purpose of this study was to relate the combination of glass transition temperature (T g) and temperature of measurement with the mechanical and compaction properties of some test materials. Methods. Copolymers with different T gs were synthesised by free radical copolymerisation of methyl methacrylate with lauryl methacrylate. Elastic moduli were measured by dynamic mechanical analysis at different strain rates and temperatures. Compaction experiments were performed at different compaction speeds and temperatures. Results. The difference between temperature of measurement and T g appears to determine both elastic modulus and yield strength completely. They both decrease with decreasing difference between temperature of measurement and Tg and increase with strain rate. At temperatures of measurement higher than the T g, the elastic modulus is extremely low because the materials behave as rubbers. Consequently, the amount of energy stored during compaction decreases when the compaction temperature approaches the T g and increases with strain rate. When the compaction temperature is higher than the T g, the amount of stored energy is extremely large. The compaction experiments show that the final tablet porosity is completely determined by stress relaxation phenomena. Consequently, the final tablet porosity follows exactly the same relation as that of stored energy. Conclusions. The final tablet porosity is unequivocally determined by the amount of stored energy. This implies that tablet production at a temperature of about 20 K under the glass transition temperature of the material yields tablets with minimum porosity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012078928297
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of hydroxy compounds on gel formation of gelatin (1997)
    Springer
    Colloid & polymer science 275 (1997), S. 67-72 
    Details
    ISSN: 1435-1536
    Keywords: Key words Gelatin ; gel formation ; NMR ; viscoelasticity ; circular dichroism
    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  Network formation of gelatin gel is known to consist of three-dimensionally cross-linked triple helices among polypeptide chains. The effects of added low molecular weight mono-ols, diols and polyols on the higher-order structure formation of gelatin chains were investigated using the following measurements: melting temperature, viscoelasticity and spin-lattice relaxation time (T 1) of H17 2O of gels, and circular dichroism spectra of diluted gelatin solutions. Furthermore, hydration behaviors of these hydroxy compounds were evaluated from the dynamic hydration numbers (n DHN) derived from T 1 of H17 2O in the solutions. It was found that network structures of gelatin gels containing hydoxy compounds were influenced by the number and position of hydroxyl groups as well as the number of carbon atoms of these coexisting compounds. The effect of hydroxyl groups of hydroxy compounds was considered to stabilize the helices among gelatin chains. Especially, the addition of polyols with large number of hydroxyl groups increased the number of cross-linking junctions in the gel networks, which consist of the aggregation among the helices. On the contrary, the effect of carbon atoms of hydroxy compounds is to disturb the formation of the helices and the aggregation among the helices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050053
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  • 7
    Electronic Resource
    Electronic Resource
    Phase separation of aqueous solution of methylcellulose (1997)
    Springer
    Colloid & polymer science 275 (1997), S. 537-545 
    Details
    ISSN: 1435-1536
    Keywords: Key words Methylcellulose ; thermogelation ; sol ; gel transition ; phase diagram ; viscoelasticity
    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  As we determined visually by the temperature cloud point method, the coexistence phase curve of methylcellulose in aqueous solution belongs to the LCST (low critical solution temperature) type. Rheological dynamic measurements reveal the existence of three gel domains. The gel (I) localized in the homogeneous phase at low concentration and low temperature, is a very weak gel, where the cross-links are attributed to pairwise hydrophobic interactions between the most hydrophobic zones of the backbone: the trimethyl blocks. The second gel (II) was revealed in the high concentration regime and below the LCST, it may be attributed to the formation of crystallites which play the role of cross-linking points. The third gel was concomitant to the micro-phase separation. In these turbid gels, syneresis develops slowly with time: the higher the temperature and the lower the concentration, the faster the syneresis. Near the three sol–gel transitions, a power law frequency dependence of the loss and storage moduli was observed and the viscoelastic exponent Δ(G′∼G″∼ωΔ) was found to be 0.76 and 0.8 and to reach 1 at high concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050116
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  • 8
    Electronic Resource
    Electronic Resource
    Viscoelasticity and diffusion in miscible blends of saturated hydrocarbon polymers (1997)
    Springer
    Rheologica acta 36 (1997), S. 217-228 
    Details
    ISSN: 1435-1528
    Keywords: Polymer melts ; miscible blends ; viscoelasticity ; tracer diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Linear viscoelasticity and tracer diffusion were investigated as functions of temperature, component molecular weight and blend composition for entangled, single-phase blends of nearly monodisperse poly(ethylene-alt-propylene) (PEP) and head-to-head polypropylene (HHPP). Both components are non-polar and, despite evidence for slight differences of component glass temperatures in their blends, the viscoelastic data obey time-temperature superposition rather well. The properties of the blends were compared at constant T-T g (blend) with predictions of the tube-model theories. The composition dependence of viscosity agrees best with the double-reptation prediction, as had been found earlier for molecular weight blends. The variation in plateau modulus with composition is consistent with reptation, but the changes are too small to provide a definitive test. The tracer diffusion coefficients, D * PEP and D * HHPP are nearly independent of composition, consistent with the reptation prediction and in sharp contrast with tracer diffusion for blends with specific associations. Results for the recoverable compliance depart from this pattern, varying differently and much less strongly with composition than the predictions of either single or double reptation. It thus seems that microstructural blends may behave in significantly more complex ways than molecular weight blends even for components with only weak dispersive interactions and rather modest differences in glass temperature and plateau modulus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366662
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  • 9
    Electronic Resource
    Electronic Resource
    Structure and dynamics of ovalbumin gels (1997)
    Springer
    Rheologica acta 36 (1997), S. 252-261 
    Details
    ISSN: 1435-1528
    Keywords: Ovalbumin ; gelation ; viscoelasticity ; SEM ; thermal behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Solvent effects on dynamical and thermal behaviors of ovalbumin (OVA) gels induced by thermal denaturation at high temperature of 160°C were studied from dynamic shear modulus measurement, shear creep and creep recovery measurement, and DSC measurement. Two organic solvents, glycerin (G) and ethylene glycol (EG), and their mixtures with water (W)(G/W and EG/W) were used as solvent for preparation of gels. Stable gels formed in pure glycerin took a fractal structure at OVA concentration C range of 15–45wt% at a temperature specific to respective C, whereas a fractal structure was not observed for gels prepared in EG, G/W, and EG/W. The results were consistent with thermal denaturation behaviors of OVA in these solvents. Morphologies of two gels prepared in water and glycerin were explored using high resolution SEM, which showed that a basic unit responsible for formation of OVA gels was spheres with a diameter ranging from 20 to 40 nm, being much larger than 5.6 nm of the diameter of native OVA, and a fractal structure was related to network formation accompanied by melting of those spheres.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366666
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  • 10
    Electronic Resource
    Electronic Resource
    Viscoelasticity and diffusion in miscible blends of saturated hydrocarbon polymers (1997)
    Springer
    Rheologica acta 36 (1997), S. 217-228 
    Details
    ISSN: 1435-1528
    Keywords: Key words Polymer melts ; miscible blends ; viscoelasticity ; tracer diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Linear viscoelasticity and tracer diffusion were investigated as functions of temperature, component molecular weight and blend composition for entangled, single-phase blends of nearly monodisperse poly(ethylene-alt-propylene) (PEP) and head-to-head polypropylene (HHPP). Both components are non-polar and, despite evidence for slight differences of component glass temperatures in their blends, the viscoelastic data obey time-temperature superposition rather well. The properties of the blends were compared at constant T–T g (blend) with predictions of the tube-model theories. The composition dependence of viscosity agrees best with the double-reptation prediction, as had been found earlier for molecular weight blends. The variation in plateau modulus with composition is consistent with reptation, but the changes are too small to provide a definitive test. The tracer diffusion coefficients, D PEP * and D HHPP * are nearly independent of composition, consistent with the reptation prediction and in sharp contrast with tracer diffusion for blends with specific associations. Results for the recoverable compliance depart from this pattern, varying differently and much less strongly with composition than the predictions of either single or double reptation. It thus seems that microstructural blends may behave in significantly more complex ways than molecular weight blends even for components with only weak dispersive interactions and rather modest differences in glass temperature and plateau modulus.
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    URL: http://dx.doi.org/10.1007/BF00366662
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  • 11
    Electronic Resource
    Electronic Resource
    Structure and dynamics of ovalbumin gels (1997)
    Springer
    Rheologica acta 36 (1997), S. 252-261 
    Details
    ISSN: 1435-1528
    Keywords: Key words Ovalbumin ; gelation ; viscoelasticity ; SEM ; thermal behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Solvent effects on dynamical and thermal behaviors of ovalbumin (OVA) gels induced by thermal denaturation at high temperature of 160°C were studied from dynamic shear modulus measurement, shear creep and creep recovery measurement, and DSC measurement. Two organic solvents, glycerin (G) and ethylene glycol (EG), and their mixtures with water (W)(G/W and EG/W) were used as solvent for preparation of gels. Stable gels formed in pure glycerin took a fractal structure at OVA concentration C range of 15–45wt% at a temperature specific to respective C, whereas a fractal structure was not observed for gels prepared in EG, G/W, and EG/W. The results were consistent with thermal denaturation behaviors of OVA in these solvents. Morphologies of two gels prepared in water and glycerin were explored using high resolution SEM, which showed that a basic unit responsible for formation of OVA gels was spheres with a diameter ranging from 20 to 40nm, being much larger than 5.6nm of the diameter of native OVA, and a fractal structure was related to network formation accompanied by melting of those spheres.
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    URL: http://dx.doi.org/10.1007/BF00366666
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  • 12
    Electronic Resource
    Electronic Resource
    Strain hardening of fibrin gels and plasma clots (1997)
    Springer
    Rheologica acta 36 (1997), S. 262-268 
    Details
    ISSN: 1435-1528
    Keywords: Key words Fibrin ; viscoelasticity ; strain hardening ; clot retraction ; platelets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Biological macromolecules have unique rheological properties that distinguish them from common synthetic polymers. Among these, fibrin has been studied extensively to understand the basic mechanisms of viscoelasticity as well as molecular mechanisms of coagulation disorders. One aspect of fibrin gel rheology that is not observed in most polymeric systems is strain hardening: an increase in shear modulus at strain amplitudes above 10%. Fibrin clots and plasma clots devoid of platelets exhibit shear moduli at strains of approximately 50% that are as much as 20 times the moduli at small strains. The strain hardening of fibrin gels was eliminated by the addition of platelets, which caused a large increase in shear storage modulus in the low strain linear viscoelastic limit. The reduction in strain hardening may result from fibrin strand retraction which occurs when platelets become activated. This interpretation is in agreement with recent theoretical treatments of semi-flexible polymer network viscoelasticity.
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    URL: http://dx.doi.org/10.1007/BF00366667
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  • 13
    Electronic Resource
    Electronic Resource
    Linear viscoelastic behavior of molten polymer blends: A comparative study of the Palierne and Lee and Park models (1997)
    Springer
    Rheologica acta 36 (1997), S. 416-428 
    Details
    ISSN: 1435-1528
    Keywords: Key words Blends ; linear ; viscoelasticity ; emulsion models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The linear viscoelastic properties of several molten blends with immiscible components of different viscosity ratio have been investigated. All the blends show a morphology of emulsion type. At low frequencies, the behaviors of these blends are essentially governed by the interface. The Palierne (1990) model is shown to well predict the linear behavior of all the blends. The Lee and Park model (1994), developed to take into account the relationship between the rheological behavior and morphological changes under large strain flows, is also shown to well describe the storage and loss moduli of the blends by adjusting a single fitting parameter. Based on the weighted relaxation spectra, a comparison of both model predictions is made focussing on the time associated to the interface. An approximate method is then proposed to evaluate the interface parameter introduced in the Lee and Park model. At high frequency, discrepancies are observed for the Lee and Park predictions when the viscoelastic properties of both components are considerably different. The description of the bulk properties of the blend, i.e., the mixing rule used by Lee and Park, is modified to obtain a better description of the high frequency data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396328
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  • 14
    Electronic Resource
    Electronic Resource
    Sticky dumbbells: from Hookean dumbbells to transient network (1997)
    Springer
    Rheologica acta 36 (1997), S. 534-543 
    Details
    ISSN: 1435-1528
    Keywords: Transient network ; Hookean dumbbell ; chemical rheology ; viscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The Green-Tobolsky theory of transient networks is merged to the Hookean dumbbell model by considering Hookean sticky dumbbells, whose beads can randomly be stuck to a network submitted to affine deformation, or be set free from the network and undergo a free diffusive Brownian motion in the solvent. Sticking to and releasing from the network is treated as an instantaneous chemical reaction. This model has a closed-form solution, in which the stress is the sum of two (resp. three) Maxwellian codeformational relaxations for dumbbells with one (resp. two) sticking beads. When Brownian diffusion is faster than the chemical kinetics, one of the modes of two-sticking beads dumbbells is the Green-Tobolsky network relaxation, whereas the other modes correspond to fast configurational relaxations. In the opposite limit of fast chemical kinetics compared to Brownian relaxation, the effect of the network is to slow down the configurational response of Hookean dumbbells. Sticky dumbbells thus realise a continuous transition from Hookean dumbbells to transient networks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00368131
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  • 15
    Electronic Resource
    Electronic Resource
    The “decaying springs” model for irreversibility in polymer melts (1997)
    Springer
    Rheologica acta 36 (1997), S. 585-589 
    Details
    ISSN: 1435-1528
    Keywords: Polymer melts ; viscoelasticity ; constitutive equations ; irreversibility ; integral models ; thermorheological behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In this work, entanglements in a polymer melt are modeled as a system of parallel springs which form and decay spontaneously. The springs are assumed to be nonlinear, and a certain fraction of them is torn apart by a certain strain. Based on these assumptions, a model of behavior in simple shear is developed. This model is shown to predict a behavior comprising that of a Wagner fluid, and is generalized to a tensorial model of single integral type. The integrand depends on a product of a material function, modeling reversible behavior, and a material functional which takes irreversible processes into account. Irreversibility of network disentanglement, which may occur when deformation changes or reverses direction, can be modeled in this way. It is shown that the two well-known Wagner constitutive equations with and without irreversibility assumptions are special cases of the model developed. In case of a deformation which does not change directions, the new material function and the material functional are multiplied to yield Wagner's damping function. When the rate of spring formation is a function of temperature, the developed model is shown to predict thermorheologically simple behavior. A constitutive equation for non-isothermal flow of polymers is developed with this assumption.
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    URL: http://dx.doi.org/10.1007/BF00368136
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  • 16
    Electronic Resource
    Electronic Resource
    Sticky dumbbells: from Hookean dumbbells to transient network (1997)
    Springer
    Rheologica acta 36 (1997), S. 534-543 
    Details
    ISSN: 1435-1528
    Keywords: Key words Transient network ; Hookean dumbbell ; chemical rheology ; viscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The Green-Tobolsky theory of transient networks is merged to the Hookean dumbbell model by considering Hookean sticky dumbbells, whose beads can randomly be stuck to a network submitted to affine deformation, or be set free from the network and undergo a free diffusive Brownian motion in the solvent. Sticking to and releasing from the network is treated as an instantaneous chemical reaction. This model has a closed-form solution, in which the stress is the sum of two (resp. three) Maxwellian codeformational relaxations for dumbbells with one (resp. two) sticking beads. When Brownian diffusion is faster than the chemical kinetics, one of the modes of two-sticking beads dumbbells is the Green-Tobolsky network relaxation, whereas the other modes correspond to fast configurational relaxations. In the opposite limit of fast chemical kinetics compared to Brownian relaxation, the effect of the network is to slow down the configurational response of Hookean dumbbells. Sticky dumbbells thus realise a continuous transition from Hookean dumbbells to transient networks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050068
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  • 17
    Electronic Resource
    Electronic Resource
    The „decaying springs” model for irreversibility in polymer melts (1997)
    Springer
    Rheologica acta 36 (1997), S. 585-589 
    Details
    ISSN: 1435-1528
    Keywords: Key words Polymer melts ; viscoelasticity ; constitutive equations ; irreversibility ; integral models ; thermorheological behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In this work, entanglements in a polymer melt are modeled as a system of parallel springs which form and decay spontaneously. The springs are assumed to be nonlinear, and a certain fraction of them is torn apart by a certain strain. Based on these assumptions, a model of behavior in simple shear is developed. This model is shown to predict a behavior comprising that of a Wagner fluid, and is generalized to a tensorial model of single integral type. The integrand depends on a product of a material function, modeling reversible behavior, and a material functional which takes irreversible processes into account. Irreversibility of network disentanglement, which may occur when deformation changes or reverses direction, can be modeled in this way. It is shown that the two well-known Wagner constitutive equations with and without irreversibility assumptions are special cases of the model developed. In case of a deformation which does not change directions, the new material function and the material functional are multiplied to yield Wagner’s damping function. When the rate of spring formation is a function of temperature, the developed model is shown to predict thermorheologically simple behavior. A constitutive equation for non-isothermal flow of polymers is developed with this assumption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050073
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  • 18
    Electronic Resource
    Electronic Resource
    Viscoelastic effects and shear-induced phase separation in polymer solutions (1997)
    Springer
    Colloid & polymer science 106 (1997), S. 150-157 
    Details
    ISSN: 1435-1536
    Keywords: Polymer solutions ; shear flow ; phase separation ; viscoelasticity
    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 We numerically investigate nonlinear regimes of shear-induced phase separation in entangled polymer solutions. For the purpose a time-dependent Ginzburg-Landau model describing the two-fluid dynamics of polymer and solvent is used. A conformation tensor is introduced as a new dynamic variable to represent chain deformations. Its variations give rise to a large viscoelastic stress. Above the coexistence curve, a dynamical steady state is attained, where fluctuations are enhanced on various spatial scales. At relatively large shear, the elongated polymer-rich regions form a transient network supporting most of the stress. Because such a network is continuously deformed in shear flow, the shear stress and the normal stress difference exhibit large fluctuations. This result explains an early observation of large temporal fluctuations of the normal stress by Lodge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01189511
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