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Wolfgang Thimm
Rheological Characterization of Polymers (PhD thesis summary)
Appl. Rheol. 13:2 (2003) 93-94 ►

► Cite this publication as follows:
Thimm W: Rheological Characterization of Polymers (PhD thesis summary), Appl. Rheol. 13 (2003) 93.

A.J. Nogueiro, J.M. Maia
On the Influence of Concentration on the Rheology of Polymer Solutions:Can Scaling Laws Be Found?
Appl. Rheol. 13:2 (2003) 87-92 ►

The present work is concerned with the study of the rheology of polymer solutions spanning different concentration regimes and originates from a former round-robin research programme on this subject, the S1 project, involving a number of research groups and institutions. The base fluid for this programme was the so-called S1 fluid, which is a 2.5% w/w solution of Polyisobutylene (PIB) in a solvent consisting of a mixture of polybutene oil and dekalin. In this paper a set of solutions having different concentrations of PIB are studied in steady shear, oscillatory shear and in axi-symmetrical contraction flows. The focus of the study is on the possibility of finding concentration scaling laws for polymer solutions spanning each or several of the concentration regimes. The results in shear flows show that it is possible to find scaling laws both for temperature and concentration in all regimes. Extensional results show that the curves superimpose within each concentration regime, but not over the whole range of concentrations. Accordingly, concentration scaling laws were then found for both shear and extension, the latter depending on the concentration regime: dilute, semi-dilute or concentrated.

► Cite this publication as follows:
Nogueiro AJ, Maia JM: On the Influence of Concentration on the Rheology of Polymer Solutions:Can Scaling Laws Be Found?, Appl. Rheol. 13 (2003) 87.

Nattapong Nithi-Uthai, Ica Manas-Zloczower
Numerical Simulation of Sharkskin Phenomena in Polymer Melts
Appl. Rheol. 13:2 (2003) 79-86 ►

A fluid dynamic analysis package, PolyFlow, based on the finite element method is used to study the sharkskin phenomenon. A stick-slip mechanism is used as the basis for the simulations. This study is aimed at illustrating how fluctuations in the stress at the exit from the die cause similar fluctuations in the extrudate swell ratio, resembling the sharkskin phenomenon. Such fluctuations in the stress at the exit from the die are produced by implementing a stickslip boundary condition at the die wall, mimicking a mechanism of molecular entanglement/disentanglement at the wall. We use a superposition of stress relaxation/stress growth and a periodic change in extrudate swell governed by the die exit stress level to depict sharkskin. Three relatively monodisperse polybutadienes were used in this study. The simulated sharkskin time period was found to be in good agreement with experimental findings. We found that the simulated pictures of sharkskin are similar for all three molecular weight samples. A comparison between the simulated sharkskin and experimental results show qualitative resemblance. The main problems preventing us from generating more quantitative sharkskin results mainly reside in the model limitations in depicting stress singularity, limitations in mesh design refinement and the constitutive model employed. In spite of these limitations, the qualitative agreement between simulation results and experimental data is good.

► Cite this publication as follows:
Nithi-Uthai N, Manas-Zloczower I: Numerical Simulation of Sharkskin Phenomena in Polymer Melts, Appl. Rheol. 13 (2003) 79.

Reni Devienne, Philippe Corvisier, Abdel Lyazid
Flow of Some Carboxymethylcellulose Solutions Through Abrupt Axisymmetric Contractions.Experimental Study and Modelling of Shear Thinning and Elongational Effects
Appl. Rheol. 13:2 (2003) 70-78 ►

The focus of this paper will be on the modelling and simulation of contraction flow, with marked aspect ratio b = 6, 9, 12. Two fluid families are considered: a glycerol Newtonian solution and carboxy-methyl-cellulose (CMC) solutions which present particular rheological properties. Their shear thinning character are modelled by a Cross formula over a large scale of shear rates. The elongational properties are taken via a simplified Ericksen model into account. Experimental velocity profiles are determined using the Laser Doppler Anemometry (L.D.A) technique. They are found to be in good agreement with numerical velocity profiles obtained using a finite volume method with extra source terms traducing the particular rheological behaviour proposed here. The simulations allow to determine the different values of an elongational parameter m3. Then, some numerical results concerning the total energy losses are presented using the usual concept of the equivalent length.

► Cite this publication as follows:
Devienne R, Corvisier P, Lyazid A: Flow of Some Carboxymethylcellulose Solutions Through Abrupt Axisymmetric Contractions.Experimental Study and Modelling of Shear Thinning and Elongational Effects, Appl. Rheol. 13 (2003) 70.

Elisabetta De Angelis
Plasma and Fluid Turbulence:Theory and Modelling (Akira Yoshizawa)
Appl. Rheol. 13:2 (2003) 69 ►

► Cite this publication as follows:
DeAngelis E: Plasma and Fluid Turbulence:Theory and Modelling (Akira Yoshizawa), Appl. Rheol. 13 (2003) 69.

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