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  • 1
    Electronic Resource
    Electronic Resource
    Elastic recovery of immiscible blends Part 2: Transient flow histories (1999)
    Springer
    Rheologica acta 38 (1999), S. 198-205 
    Details
    ISSN: 1435-1528
    Keywords: Key words Immiscible blends ; Flow-induced morphology ; Blend rheology ; Recoil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Immiscible polymer blends are known to display an unusual elastic recovery after stress release. Recoil after steady-state shearing is well understood and obeys specific scaling relations. Releasing the stress before the steady-state morphology has been reached results in a more complex elastic recovery, including very large final values. This behaviour is investigated systematically. Model blends are used, consisting of nearly inelastic components; hence the measured recoil can be attributed totally to contributions from the interface. The instantaneous structure at the onset of the recoil can vary greatly in transient experiments, ranging from slightly deformed droplets to highly elongated filaments. The effects of this initial structure on the ultimate recoil and time scale of the recovery are studied. The morphological changes during recovery are considered as well. It is demonstrated that they can be computed from the normal stresses during stress relaxation with comparable initial morphologies. This indicates that the same morphological changes occur during stress relaxation and constrained recoil. A scaling relation for the recoil curves has been derived from the Doi-Ohta theory, which is confirmed by the experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050169
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  • 2
    Electronic Resource
    Electronic Resource
    Manifestation of phase separation processes in oscillatory shear: droplet-matrix systems versus co-continuous morphologies (1999)
    Springer
    Rheologica acta 38 (1999), S. 274-286 
    Details
    ISSN: 1435-1528
    Keywords: Key words Phase separation ; Rheology ; Polymer blends ; Dynamic measurements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Phase separation processes in mixtures of poly-α-methylstyrene-co-acrylonitrile (PαMSAN) and poly-methylmethacrylate (PMMA) with lower critical solution temperature (LCST) behavior have been studied, focusing on the manifestation of the interface in oscillatory shear measurements. By using blends of different composition, systems with a droplet-matrix morphology or a co-continuous structure are generated during the phase separation process. The feasibility of probing this morphology development by rheological measurements has been investigated. The development of a disperse droplet phase leads to an increase in the elasticity of the blend at low frequency, showing up as a shoulder in the plot of storage modulus versus frequency. Here, the droplet growth is unaffected by the shear amplitude up to strains of 0.2; therefore the resulting dynamic data are suitable for quantitative analysis. In contrast, for blends in which phase separation leads to a co-continuous structure, the storage modulus shows a power law behavior at low frequency and its value decreases as time proceeds. For the latter systems, effects of the dynamic measurement on the morphology development have been observed, even for strain amplitudes as low as 0.01. To probe the kinetics of morphology evolution in droplet-matrix systems, measurements of the time dependence of the dynamic moduli at fixed frequency should be performed (for a whole series of frequencies). Only from such measurements, curves of the frequency dependence of the moduli at a well defined residence time can be constructed. From fitting these curves to the emulsion model of Palierne, the droplet diameter distribution at that particular stage in the phase separation and growth process can be obtained. It is not appropriate to use a simplified version of the Palierne model containing only the average droplet size, because a morphology with too broad a size distribution is generated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050179
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  • 3
    Electronic Resource
    Electronic Resource
    Stress relaxation as a microstructural probe for immiscible polymer blends (1997)
    Springer
    Rheologica acta 36 (1997), S. 513-523 
    Details
    ISSN: 1435-1528
    Keywords: Key words Immiscible blends ; stress relaxation ; Rayleigh instabilities ; blend morphology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Relaxation has been investigated in immiscible blends that consist of slightly viscoelastic components. Both the shear and normal stresses have been measured after cessation of steady shear flow as well as after transient shear histories. The latter can generate a fibrillar structure which can relax by either retraction or break-up via end-pinching or Rayleigh instabilities. Each of these three relaxation mechanisms is reflected in the shape of the stress curves, from which also the corresponding structural time scales can be deduced. The experimental results have been used to evaluate the Doi-Ohta and Lee-Park models for immiscible blends. The scaling relations by Doi-Ohta are confirmed by the experimental results, but none of the existing models can correctly predict the complex relaxation behaviour observed for a highly deformed droplet phase. In the present study an alternative approach has been proposed. The stress relaxation due to fibril break-up via Rayleigh instabilities has been predicted successfully by combining physical models for the structural changes with the basic approach of the Doi-Ohta model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050066
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  • 4
    Electronic Resource
    Electronic Resource
    Stress relaxation as a microstructural probe for immiscible polymer blends (1997)
    Springer
    Rheologica acta 36 (1997), S. 513-523 
    Details
    ISSN: 1435-1528
    Keywords: Immiscible blends ; stress relaxation ; Rayleigh instabilities ; blend morphology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Relaxation has been investigated in immiscible blends that consist of slightly viscoelastic components. Both the shear and normal stresses have been measured after cessation of steady shear flow as well as after transient shear histories. The latter can generate a fibrillar structure which can relax by either retraction or break-up via end-pinching or Rayleigh instabilities. Each of these three relaxation mechanisms is reflected in the shape of the stress curves, from which also the corresponding structural time scales can be deduced. The experimental results have been used to evaluate the Doi-Ohta and Lee-Park models for immiscible blends. The scaling relations by Doi-Ohta are confirmed by the experimental results, but none of the existing models can correctly predict the complex relaxation behaviour observed for a highly deformed droplet phase. In the present study an alternative approach has been proposed. The stress relaxation due to fibril break-up via Rayleigh instabilities has been predicted successfully by combining physical models for the structural changes with the basic approach of the Doi-Ohta model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00368129
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