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• Polymer and Materials Science  (4)
• Non-linear viscoelasticity  (1)
• Rheological equation  (1)
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• 1
Electronic Resource
Springer
Rheologica acta 38 (1999), S. 14-25
ISSN: 1435-1528
Keywords: Key words Fumed silica ; Colloidal suspensions ; Non-linear viscoelasticity ; Rheological models
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract Suspensions of fumed silica exhibit a wide range of rheological properties depending on the nature and magnitude of the interparticle forces. In a non-polar fluid, the particles interact through hydrogen bonding and can form a three-dimensional network. The microstructure formation is responsible for the non-linear viscoelastic behavior of fumed silica suspensions, even at very small strain. These non-linear rheological properties have been studied in small amplitude oscillatory experiments as a function of particle size, surface treatment of particles, suspending medium polarity and solids concentration. The non-linear viscoelastic behavior is characterized by a non-sinusoidal waveform of the signal response. For suspensions in a non-polar fluid, both the elastic and the loss moduli are shown to be sensitive to the strain amplitude: the elastic modulus is decreasing with increasing strain whereas the loss moduli is initially increasing with strain. We have chosen to examine the dissipated energy which is clearly related to the breakup of the suspension structure. A comparison of model predictions and the experimental data shows the limitations of these models, recently proposed in the literature to describe the behavior of colloidal suspensions.
Type of Medium: Electronic Resource
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• 2
Electronic Resource
Springer
Rheologica acta 27 (1988), S. 241-254
ISSN: 1435-1528
Keywords: Rheological equation ; dilute polymersolution ; polyelectrolyte ; shear thickening ; polyacrylamide solution
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract A mathematical model based on the diffusion-convection equations is used to describe the rheological properties of dilute polymer solutions. The model uses a second-order conformation tensor as a measure of the internal strain; this avoids the mathematical complexity resulting from the use of a more detailed description of the macromolecules and also avoids the necessity of introducing additional ad-hoc assumptions (closure approximations) commonly used in other molecular theories. The rheological equation is obtained in terms of the rate-of-deformation tensor $$\dot \gamma$$ and a scalar functionf(σ) relating the extra stress tensorσ to the internal strain tensorc. The functionf(σ) depends on the physical insight introduced in the Helmholtz free energyA(c) of the solvent-polymer system. This approach is illustrated for an intra-molecular potential of a “FENE-charged” type. The concept of an isotropic, but conformation-dependent, friction coefficient, is also introduced to account for the “coil-stretch” transformation of macromolecules in solution. Viscosity and first normal-stress data, of partially hydrolyzed polyacrylamide solutions, (polyelectrolytes) are analyzed and compared to the model predictions in steady shear and elongational flows.
Type of Medium: Electronic Resource
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• 3
Electronic Resource
Hoboken, NJ : Wiley-Blackwell
Advances in Polymer Technology 6 (1986), S. 407-407
ISSN: 0730-6679
Keywords: Chemistry ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Type of Medium: Electronic Resource
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• 4
Electronic Resource
Bognor Regis [u.a.] : Wiley-Blackwell
ISSN: 0887-6266
Keywords: Chemistry ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Linear low-density polyethylenes (LLDPES) and polypropylene (PP) have been recovered from solutions of varying initial polymer concentration. Melts of these polymers show significant reductions in viscosity and elasticity, and the effects are attributed to changes in the entanglement density of the polymer. Measurements of entanglement densities have been attempted from experimental values of the apparent zero-shear melt viscosity. These indicate that solution treatments in trichlorobenzene at 135°C reduce the entanglement density more effectively in PP than in LLDPE. In all cases the observed effects are reversible by annealing at elevated temperatures. Analytic data point to entanglement changes as the true origin of changes in viscoelastic properties, since solution treatments produce no changes in molecular weights and weight distributions, and the samples tested are free of solvent residues.
Type of Medium: Electronic Resource
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• 5
Electronic Resource
New York, NY [u.a.] : Wiley-Blackwell
Journal of Applied Polymer Science 43 (1991), S. 543-551
ISSN: 0021-8995
Keywords: Chemistry ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
Notes: Mechanical properties of high density polyethylene (HDPE) extended to draw ratios in the 20-40 range have been determined and compared with corresponding properties of the polymers containing particulates including rutile, carbon black, iron oxide, and mica. Shrinkage of drawn structures was studied to temperatures near the fusion of the polymer host. The degree of interaction at polymer/additive interfaces was varied by surface coating certain of the solids with standard coupling agents. Solids were found to increase tensile moduli and to decrease shrinkage, particularly at higher exposure temperatures. The magnitude of changes due to the presence of solids was shown to depend on the apparent interaction at contacts between host and additive. In a dispersion-force matrix, like HDPE, benefits were optimized when the particulates were amphoteric or neutral, rather than having pronounced acid or base interaction potentials.
Type of Medium: Electronic Resource
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• 6
Electronic Resource
Bognor Regis [u.a.] : Wiley-Blackwell
ISSN: 0887-6266
Keywords: interfacial tension ; breaking thread ; polyamide ; polyethylene ; interface ; modifier morphology ; Physics ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Compared to the dynamic mixing process used in melt blending operations, most techniques for measuring the interfacial tension can be considered as virtually static. For this reason, in order to measure the interfacial tension of an A-B immiscible system in the presence of an interfacial modifier, the problem of migrating the modifier to the interface is a central issue. In this study, the influence of the addition of an interfacial modifier, a polyethylene copolymer ionomer, on the interfacial tension between two high-density polyethylenes and a polyamide is investigated. The breaking thread method is used and the interfacial tension is measured as a function of ionomer content. In order to enhance the likelihood of placing the modifier in closer proximity to the interface, various sample preparations are compared. In all cases, the interfacial tension significantly drops with increasing ionomer content and tends to a limiting value. It is shown, however, that the preparation of the system for the breaking thread experiment via coextrusion using a conical die brings the modifier in closest proximity to the interface. With this approach an additional 1.45 times reduction of the interfacial tension at 10% compatibilizer concentration (based on the mass of HDPE) is observed compared to the classical technique of preparation. Confirmation of this effect is demonstrated using X-ray photoelectron spectroscopy where analysis of the thread surface of the system prepared by coextrusion indicates a more than fourfold enrichment of interfacial modifier. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1947-1958, 1998