## Appl Rheol online available publications for selected issue

Follow the blue link(s) below for abstracts and full text pdfs .

Strain rate frequency superposition (SRFS) has been suggested as new method to extend the frequency range for assessment of the complex storage modulus G* of soft glassy materials to lower frequencies. The basic idea is that relaxation processes in such fluids are accelerated by an external shear field, analogous to the effect of a temperature shift in polymer melts and solutions. Master curves for G' and G'' are constructed from the apparent modulus data determined from non-linear oscillatory shear experiments. Here we validate the SRFS principle for the first time by independent experiments and also demonstrate its limitations.We compare SRFS results to directly measured G', G'' at frequencies down to 10-3 rad/s and creep experiments lasting up to 104 s for a variety of gel-like fluids, including polymeric thickener solutions, a highly concentrated w/oemulsion, and wormlike micellar surfactant solutions, as well as a weakly viscoelastic non-Brownian suspension of glass beads. Good agreement between SRFS data and directly measured G', G'' values for the thickener solutions, the emulsion as well as the suspension. Apparent viscosity data obtained from creep experiments and absolute values of the complex viscosity in the low frequency limit agree fairly well for these fluids. But the method fails for the wormlike micellar solutions and this could be due to non-uniform flow or due to flow-induced structural changes. Finally,we demonstrate that the combination of SRFS, rotational rheometry, and advanced high frequency rheology methods allows for a broad bandwidth characterization of complex fluids spanning an unprecedented frequency range of about eleven decades.► Cite this publication as follows:

Kowalczyk A, Hochstein B, Stahle P, Willenbacher N: Characterization of complex fluids at very low frequency: experimental verification of the strain rate-frequency superposition (SRFS) method, Appl. Rheol. 20 (2010) 52340.

Results are presented aiming to determine whether wall slip occurs while performing rheological measurements of Carbopol solutions and bentonite dispersions at different concentrations using a standard oil-field Couette-type viscometer with two gap sizes. Yield stresses using a vane rheometer were also determined and compared to those obtained by extension of the experimentally-derived rheological curves at the Couette viscometer.The results show that, if preparation procedures are followed as suggested for Carbopol solutions and by API standard for drilling fluids, simulating either the pre-shearing in the rig mud pumps or in the bit nozzles during drilling operations, wall slip does not occur, with a good agreement of the rheograms and of the yield stresses determined for both gap sizes of the Couette viscometer and by the vane rheometer. No slip occurs also for CMC solutions which exhibited pseudoplastic power-law behavior.► Cite this publication as follows:

Kelessidis VC, Hatzistamou V, Maglione R: Wall slip phenomenon assessment of yield stress pseudoplastic fluids in Couette geometry, Appl. Rheol. 20 (2010) 52656.

This paper is concerned with the determination of the constitutive parameters of low concentrations of the complex fluid polyethylene glycol (PEO). Velocity fields of PEO solutions in a microfluidic T-junction have been measured for pressure driven flow using micron resolution particle image velocimetry. As the fluid is forced to turn the corner of the T-junction a range of shear rates, and therefore viscosities, is produced.Thus it is possible to establish the rheological profile from a single experiment. An inverse method used in conjunction with a finite element model was used to determine the constitutive parameters of the fluid, estimated to within 1.5 % error in all three cases considered.► Cite this publication as follows:

Bandulasena HC, Zimmerman WB, Rees JM: Rheometry of non-Newtonian polymer solution using microchannel pressure driven flow, Appl. Rheol. 20 (2010) 55608.

Aqueous solutions of F127 pluronic systems exhibit an interesting thermal gelation above a certain concentration. This phenomenon concerns the transition from a liquid-like behavior at low temperatures to a solid-like behavior at high temperatures, and it is due to different temperature responses from the different polymer segments, polypropylene oxide (PPO) and polyethylene oxide (PEO). Such property leads to a structural change in the self assembled macromolecule upon heating, from an isotropic micellar structure to an ordered cubic structure. These two types of assembly are clearly distinct with respect to their rheological behavior.This contribution emphasizes the rheological properties of the pluronic system in micellar and cubic phase, in combination with NMR, Dynamic Light Scattering and DSC information. The results emphasize the gelation process upon heating and a cubic phase characterized by higher storage modulus and higher A and z Weak Gel Model exponents than the micellar phase. Micellar growth upon heating was found within micellar phase. The presented data support the hypothesis that each polymer segment actively participates in the formation of the different phases: while PPO is responsible for micelle formation, PEO plays a dominating role in cubic phase formation. Finally, different stiffness between the core and the corona of the aggregates in the two phases is observed.► Cite this publication as follows:

Gentile L, DeLuca G, Antunes FE, OlivieroRossi C, Ranieri GA: Thermogelation Analysis Of F127-Water Mixtures By Physical Chemistry Techniques, Appl. Rheol. 20 (2010) 52081.

Electrorheological (ER) and dielectric properties of silicone-oil suspensions of polyaniline (PANI) particles protonated with phosphoric and tetrafluoroboric acids to various doping level have been investigated. The particle conductivity was thus varied between the order of 10^{-9}S/cm and 10^{-4}S/cm. The dynamic yield stresses obtained at controlled shear rate mode viscometry, the storage moduli from the oscillatory shear experiments and the dielectric relaxation times from frequency dependences of dielectric constant and loss factor were used as criteria of rigidity or elasticity of ER structures and particle mobility in the electric field. The conductivity of suspension particles plays a decisive role in their ER behaviour. The ER efficiency increased as conductivity of dispersed particles raised, irrespective of the type of employed acid used for the protonation of PANI.► Cite this publication as follows:

Stenicka M, Pavlinek V, Saha P, Blinova NV, Stejskal J, Quadrat O: Electrorheology of suspensions of variously protonated polyaniline particles under steady and oscillatory shear, Appl. Rheol. 20 (2010) 55371.

Thixotropy is an important rheological behavior of waxy crude oils. The objective of this paper is to demonstrate existing model's abilities to describe shear stress decay behaviors of waxy crude oils at constant shear rates. Seven models specially developed for or currently used to waxy crude oils are reviewed as well as two viscoelastic-thixotropic models for human blood. Stress decay behaviors were measured for four waxy crude oils and at various temperatures. Each of the models was used to fit the stress decay plots at a single shear rate, and at multiple shear rates, respectively. Globally, Zhao's model, a complex viscoplatic model with two structure parameters and twelve physical & fitting parameters,matched the experimental plots better than other compared models. While the three models with viscoelastic backgrounds were not quite successful. For use of models, one may make choice by comprehensively considering a model's complexity in mathematic form and abilities to describe the rheological behaviors.► Cite this publication as follows:

Zhang J, Guo L, Teng H: Evaluation of thixotropic models for waxy crude oils based on shear stress decay at constant shear rates, Appl. Rheol. 20 (2010) 53944.

► Cite this publication as follows:

Ghirisan A, Broboana D, Balan C: 1st SRR - Summer School of Rheology 2010, Appl. Rheol. 20 (2010) 305.

© Applied Rheology 2019