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Rheology Step 2 training - continuation training in application of rheological concepts and techniques - viscosity, viscoelasticity and measuring techniques
Appl. Rheol. 27:6 (2017) 45-46 ►
► Cite this publication as follows:
Sahlstrom A: Rheology Step 2 training - continuation training in application of rheological concepts and techniques - viscosity, viscoelasticity and measuring techniques, Appl. Rheol. 27 (2017) 45.
Maria Jesus Hernandez Lucas, Teresa Sanz Taberner, Ana Salvador Alcaraz, Francisco J. Rubio Hernandez, Roberto Steinbruggen
Appl. Rheol. 27:6 (2017) 42-44 ►
► Cite this publication as follows:
HernandezLucas MJ, SanzTaberner T, SalvadorAlcaraz A, RubioHernandez FJ, Steinbruggen R: IBEREO 2017, Appl. Rheol. 27 (2017) 42.
Maryam Kiumarsi, Ali Rafe, Samira Yeganehzad
Effect of different bulk sweeteners on the dynamic oscillatory and shear rheology of chocolate
Appl. Rheol. 27:6 (2017) 64123 (9 pages) ►
Effect of different bulk sweeteners including maltitol, isomalt and inulin on the steady and dynamic rheological behaviors as well as chocolate structure was investigated. All the chocolate samples showed shear-thinning behavior, which was mainly affected by the shear rates. Among different rheological models, the power law model was the suitable one (high R2) for the chocolate samples containing bulk sweeteners. As the bulk sweetener has the more solid volume fraction, the more flow behavior index n was obtained. Bulk sweeteners depending on their molecular structures were influenced on the apparent viscosity and yield stress. The mechanical spectra of chocolate showed the liquid-like behavior of inulin and maltitol and solid- like behavior of sucrose and isomalt. It was also revealed that the chocolate network structure was completely influenced by temperature and related to the frequency range. During thermal processing, the bulk sweeteners did not have any effect on the chocolate consistency and they cause to reduce the network strength of the chocolate. In addition, the critical stress was sensitive to the type of bulk-sweeteners in the chocolate. Consequently, chocolate can be considered as a weak dispersion which makes aggregates and can be modeled by the weak physical gel model. Current research realized great insight to the chocolate rheology in different processes such as enrobing, shell formation and molding.► Cite this publication as follows:
Kiumarsi M, Rafe A, Yeganehzad S: Effect of different bulk sweeteners on the dynamic oscillatory and shear rheology of chocolate, Appl. Rheol. 27 (2017) 64123.
Alexandre Rothan, Rene Muller, Pascal Hebraud, Mickael Castro, Michel Bouquey, Christophe Serra
Unusual time dependent rheological behavior of a concentrated suspension
Appl. Rheol. 27:6 (2017) 64182 (7 pages) ►
The time dependent rheological behavior of a concentrated CaCO3 particle suspension is studied. The particles are suspended in a mixture of three industrial products: two resins, composed of styrene monomer, a styrene-butadiene-styrene block copolymer, and an unsaturated polyester oligomer, and one surfactant, acting as a dispersing agent for the particles. For the measurements, a MCR 301 rheometer from Anton Paar is used in the rotational mode, with a Couette geometry. An unusual behavior is observed, in which the low shear-rate viscosity of the suspension depends in a non-monotonous way on the shear rate applied during a previous shear history. The viscosity of the suspension at low shear rate depends both on the value of the prior shear rate, and the time during which it is applied. We found that the phenomenon is more pronounced when the particles volume fraction is increased. We propose an interpretation of the observed phenomenon in which links of different strengths can be formed between the particles and only the weakest links are destroyed by moderate shear rates.► Cite this publication as follows:
Rothan A, Muller R, Hebraud P, Castro M, Bouquey M, Serra C: Unusual time dependent rheological behavior of a concentrated suspension, Appl. Rheol. 27 (2017) 64182.
Uranbileg Daalkhaijav, Travis W. Walker
Developing a Nondestructive Technique for Measuring Bulk Rheology of Pseudomonas Aeruginosa Biofilm
Appl. Rheol. 27:6 (2017) 64033 (10 pages) ►
Bacterial cultures, when under appropriate conditions, will grow into a biofilm. This weak hydrogel, composed of a complex conglomeration of bacterial clusters and extrapolymeric substances, serves to protect and insulate the bacteria from mechanical disturbances and environmental perturbations that may include antibiotics. Measuring the bulk rheology of the biofilm provides a quantitative description of the macroscopic structural integrity of the soft solid, which can be used to evaluate the efficacy of techniques that are often directed at their removal or prevention. Techniques for measuring the rheology of biofilms vary significantly, ranging from filtering or scraping the biofilm from its growth medium to attempting to grow the biofilm directly on the geometry of the rheometer. In this study, we developed a protocol for measuring the bulk rheology of a biofilm that was grown in a liquid medium. By keeping the biofilm intact from its growth phase through its rheological measurement, this method allows the mechanical strength of the biofilm to be probed without compromising its integrity. Presented in the form of case studies, the results from this study confirmed the gel-like structure of the biofilm of the wild-type strain of Pseudomonas aeruginosa (PAO1). The flexibility of this protocol was shown by varying the incubation time of the biofilm from 4 to 9 days, providing a bulk elastic modulus that varied over two orders of magnitude and a yield stress that varied by an order of magnitude. Finally, in an attempt to demonstrate the fragility of biofilm, measurements were also taken on samples that were simply transferred from their incubated Petri dish to the rheometer. Results from the mechanical robustness of the biofilm are highlighted to emphasize the importance of understanding and addressing the mechanical strength of the biofilm system before attempting to remove the bacterial contamination through chemical or mechanical means.► Cite this publication as follows:
Daalkhaijav U, Walker TW: Developing a Nondestructive Technique for Measuring Bulk Rheology of Pseudomonas Aeruginosa Biofilm, Appl. Rheol. 27 (2017) 64033.
Mohammadreza Shafiei, Steve Bryant, Matthew Balhoff, Chun Huh, Roger T. Bonnecaze
Hydrogel Formulation for Sealing Cracked Wellbores for CO2 Storage
Appl. Rheol. 27:6 (2017) 64433 (8 pages) ►
A challenge for underground CO2 storage is the leakage of the buoyant supercritical gas through microcracks in wellbores that cannot be sealed with current oilfield cements that are too viscous and cannot penetrate the cracks. Polymer gels consisting of pH-sensitive hydrogel particles suspended in an aqueous solution offer a potential alternative. The rheology of aqueous solutions of Carbopol 934 as a model pH-sensitive gel is measured to find the compositions and pHs for both ease of injection and to seal cracks against the flow of bulk CO2 and CO2 dissolved in brine. The polymer gels have low viscosity at low pH and can easily flow into the microcracks. In the elevated pH of the microcracks, the particles swell creating a significant yield stress sufficient to seal leakage pathways. The yield stress reaches a maximum at pH 5 and it increases with increasing concentration. The flow curves of stress versus shear rate for all pHs and concentrations are well-described by the Herschel-Bulkley model with an exponent of about 0.34 except for highly acidic conditions when the gelant solutions show a much lower yield stresses and higher exponents. The flow curves can be collapsed onto a single universal flow curve rescaled with the yield stress, the low frequency shear modulus and the suspending fluid viscosity. The presence of salts, especially high valence salts, reduce the yield stress of the gels considerably. It is shown that the addition of chelating agents mitigates this effect and can restore more than 30% of the yield stress of the gelant.► Cite this publication as follows:
Shafiei M, Bryant S, Balhoff M, Huh C, Bonnecaze RT: Hydrogel Formulation for Sealing Cracked Wellbores for CO2 Storage , Appl. Rheol. 27 (2017) 64433.
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