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Viscous Behavior (viscous + behavior)
Selected AbstractsRheological properties of magnetic fluids and their microstructural backgroundGAMM - MITTEILUNGEN, Issue 1 2007S. Odenbach Abstract Beyond the changes exerted by magnetic fields on the flows and properties of suspensions of magnetic nanoparticles, the change of their viscous behavior attracts ongoing research interest since nearly four decades. Within this contribution we'll review the general rheological features of ferrofluids and will present theoretical explanations on microstructural basis providing an insight in the mechanisms leading to a magnetic field dependence of ferrofluid's rheology. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] DEVELOPMENT OF A SOY-BASED CREAM CHEESEJOURNAL OF TEXTURE STUDIES, Issue 6 2008MUSFIRAH ZULKURNAIN ABSTRACT Various amounts of blended tofu, oil, salt, carrageenan, pectin and maltodextrin were used to develop soy cream cheese products that were trans fat free, with texture properties similar to those of commercial dairy cream cheese. Response surface methodology predicted three formulations with similar spreadability value of that obtained from commercial cheese. Carrageenan and salt were useful to impart the desired firmness, while maltodextrin provided body to the product. Pectin introduced viscous behavior to the final texture but was proven useful in preventing syneresis. Rheological study at 25 and 4C manifested that, although the developed products mimicked the texture of the commercial sample, they had less elasticity. Chemical analysis revealed that the soy cream cheeses had lower fat and higher protein and fiber contents than the commercial sample. They were also stable against syneresis and oil separation over storage of 20 days. PRACTICAL APPLICATIONS The production of soy-based products as alternatives to dairy products has attracted much attention recently. In addition to their lactose-free and reduced fat content, soy-based products are also a good source of protein. There has yet to be any published data on the development of a soy-derivative cream cheese. This paper emphasizes the rheological development of soy cream cheeses in the presence of food hydrocolloids. Their main and interaction effects on texture properties were assessed to mimic those of dairy cream cheese. A comprehensive and systematic approach of formulating the soy cream cheeses was applied by using response surface methodology. In addition, the chemical and nutritional properties of the products were also evaluated and compared with those of the commercial dairy counterpart. [source] Simulation of the Stress-Assisted Densification Behavior of a Powder Compact: Effect of Constitutive LawsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008Héctor Camacho-Montes The densification of powders with linear and nonlinear viscous behavior (Scherer and Riedel models) and with power-law-deformation (Khun,McMeeking) behavior was studied under hot pressing and sintering forging conditions. Several numerical experiments, designated cases in this work, were performed to study the effect of (i) the uniaxial stress exerted by the piston and (ii) the rate of the uniaxial stress. The stress state was calculated using the finite-element program ANSYS for each case. Considering the mesoscopic behavior of the powders, densification rates were obtained. The similarities and differences between predictions from the three constitutive models are highlighted. The relationship between the constitutive behavior and the most effective stress state is one of the focuses of this study. For example, we show that under constant stress loading, hot pressing more effectively promotes densification than sinter forging for constitutive behaviors that do not follow the power-law creep. In general, as expected, the increase of uniaxial applied stress and piston velocity favored densification. However, the increase in densification depends strongly on the constitutive law. [source] Effect of Green Density on the Thermomechanical Properties of a Ceramic During SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Sam E. Schoenberg The thermomechanical properties of a commercial barium titanate were experimentally or theoretically determined for samples with green densities ranging from 45% to 55%. For stresses less than 300 kPa, sample deformation was determined to be linear viscous for all three stages of sintering. The shrinkage rates at a given temperature can differ by up to ,25% as the green density changes from 45% to 55%, and the maximum shrinkage rate increased with decreasing green density. The increase in shrinkage rate with lower green density samples persisted through the final sintering stage. The viscosity was determined by cyclic loading dilatometry to range from 5 to 6 GPa·s in the initial stage of sintering, to 2 GPa·s in the intermediate stage, and to increase to 10,20 GPa·s for all specimens in the final stage of sintering. Differences in the final-stage viscosity were attributed to grain size differences. Relaxation times for the sintering body were estimated to be less than 1 s, indicating that viscous behavior is dominant throughout the sintering process. [source] Structure-to-Properties Relationship of Aliphatic Hyperbranched PolyestersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 13 2007Abstract We investigated the effects of annealing on the rearrangement of the H-bond network microstructure and its influence on the thermal and rheological properties of the second pseudo-generation hyperbranched (HB) polyester based on 2,2-bis(methylol)propionic acid (Boltorn H20) in comparison to the fourth pseudo-generation HB polyester (Boltorn H40). During annealing the hydroxyl groups of HB polyesters form H-bonds with other hydroxyl or carbonyl groups. The formation of OH,OH H-bonds is favored at shorter annealing times, higher annealing temperatures, and for low pseudo-generation HB polyester, which has a low average molar mass, degree of branching, and core functionality. At temperatures up to 80,°C, Boltorn H20 indicates faster and more extensive H-bond formation as compared to Boltorn H40. This is reflected in its larger cleavage enthalpies and higher elastic contribution to the viscoelastic response. At 90,°C and above, the process of H-bond formation is delayed. Therefore, Boltorn H20 exhibits only viscous behavior in rheological measurements, and in DSC curves it shows strong exothermic transitions while heating the sample. [source] Study of pseudo-multilayer structures based on starch-polycaprolactone extruded blendsPOLYMER ENGINEERING & SCIENCE, Issue 6 2009Laurent Bélard This article is focused on the analysis of the structure-process relationships of biodegradable materials. It is mainly focused on the analysis of phase separation phenomenon occurring during the extrusion of plasticized starch/polycaprolactone blends, in a slit die. Rheological characterizations are carried out, in-line in an instrumented slit die at the exit of the extruder and, out-line with different rheometers. In certain conditions, a pseudo-multilayer structure can be generated with a polyester rich skin. Then, Electron Spectroscopy for Chemical Analysis (ESCA) and Fourier Transformed Infrared Attenuated Total Reflectance (FTIR-ATR) analyses are conducted to evaluate semi-quantitatively the polyester surface enrichment. In the range of available shear rates, the phase separation is mainly driven by the molecular weight of polycaprolactone, linked to its molten state viscosity. Three zones of surface enrichment, dependent on the molecular weights, are identified. Above 60,000 g·mol,1, no surface enrichment could be detected; below 37,000 g·mol,1, the phase separation occurs with no dependence on the processing conditions; between these two limits, the phase separation depends on both, the formulation and the processing conditions. A correlation between the rheological measurements and the phase separation is given. A predictive criterion based on the viscous behavior of the blend is established. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] | ||||||||||