Showing papers on "Apparent viscosity published in 2001"

Depletion Flocculation of Beverage Emulsions by Gum Arabic and Modified Starch

Abstract: The creaming velocity, apparent viscosity, and ultrasonic attenuation spectra (1 to 50 MHz) of 5 wt% n hexadecane oil-in-water emulsions containing different droplet radii (r = 0.15 - 0.7 μm), biopolymer types (gum arabic or modified starch), and biopolymer concentrations (0 to 2.5 wt%) were measured. Depletion flocculation was observed in the emulsions when the nonabsorbed biopolymer concentration exceeded a critical concentration (CFC). The CFC increased with decreasing droplet radius for both biopolymers because the magnitude of the depletion attraction increases with droplet size. The CFC was lower for gum arabic than modified starch because it has a higher effective volume in solution. Depletion flocculation led to an increase in creaming instability and apparent viscosity of the emulsions. Flocculation could be nondestructively monitored by measuring the decrease in ultrasonic attenuation of the emulsions. These results show that depletion flocculation by gum arabic and modified starch can have an adverse effect on the stability of beverage emulsions.

A New Free Volume Model for Dynamic Viscosity and Density of Dense Fluids Versus Pressure and Temperature

Abstract: This article presents a model based on the free volume concept, which describes the variations of dynamic viscosity and density versus temperature and pressure for the dense fluids (density > 200 kg · m−3). This model involves 6 constants for each pure compound: 3 for viscosity and 4 for density (1 constant is common to both quantities). Moreover if the viscosity and the density are known at a pressure and temperature of reference, it is sufficient to use 4 constants per pure compound. If the density is assumed to be known the model fits the viscosity data with an average absolute deviation of 3.8% for 3297 data corresponding to 41 very different pure compounds (alkanes, alkylbenzenes, cycloalkanes, alcohols, carbon dioxide, refrigerants). If the pressure is lower than 110MPa the average absolute deviation is 2.8% for viscosity (2977 points). The model gives also good results for water (3.6%). If the density is unknown, for pressures lower than 110MPa the model represents viscosity with an averag...

Rheology of non-Brownian rigid fiber suspensions with adhesive contacts

Abstract: An experimental investigation is undertaken into the shear-thinning behavior of suspensions of non-Brownian rigid fibers in Newtonian fluids. In particular, the influence of the shear stress and the fiber concentration is investigated. The shear stress is adjusted by varying both the shear rate and the solvent viscosity. In the semidilute concentration regime, where direct mechanical contacts between fibers are rare, the suspension is found to be nearly Newtonian over the stress range investigated. In the concentrated regime, the suspension becomes shear thinning below a certain shear rate. The shear thinning increases with concentration and decreases with solvent viscosity. Although shear-thinning behavior of fiber suspensions has often been reported in the literature, its physical origins are not well understood. Our experiments are interpreted in terms of the formation and breakage of fiber flocs due to the competition between hydrodynamic and colloidal forces. Our interpretation is confirmed by measurements of the adhesive forces between two individual fibers.

Direct‐Write Fabrication of Pb(Nb,Zr,Ti)O3 Devices: Influence of Paste Rheology on Print Morphology and Component Properties

Abstract: Lead niobium zirconate titanate (PNZT) pastes with tailored rheological properties have been developed for direct-write fabrication of thick-film capacitor elements in highly integrated, multifunctional electroceramic devices. Such pastes exhibited pseudoplastic behavior with a low shear apparent viscosity of roughly 1 10 6 cP. On aging, the degree of shear thinning and the low shear apparent viscosity decreased. Pastes prepared from as-received powders attained printable, steady-state viscosities of 2 10 5 cP after 50 days of aging. In contrast, pastes prepared from dispersant-coated powders showed no measurable rheological changes after 1 day of aging. Square elements were patterned on dense alumina substrates or Teflon sheets. Leveling behavior as a function of time for single line prints, and the resulting surface topographies of dried PNZT films were measured by laser profilometry. PNZT layers sintered at varying temperatures between 950° and 1050°C fo r5hi neither air or a lead-rich atmosphere yielded porous microstructures as revealed by scanning electron microscopy (SEM). Such layers exhibited dielectric constants (K) of 1400 –1570 at 1 kHz with dissipation factors (D )o f less than 4.1%.

Newtonian and non-Newtonian viscosity of supercooled liquid in metallic glasses

Abstract: We have investigated the viscosity of the supercooled liquids over a wide range of strain rate by constant-strain-rate tensile tests for La 55 Al 25 Ni 20 , Zr 65 Al 10 Ni 10 Cu 15 and Pd 40 Cu 40 P 20 (at.%) metallic glasses. The supercooled liquids exhibited Newtonian viscosity (equilibrium state) that transferred to a non-Newtonian viscosity (non-equilibrium state) with increasing temperature. The critical strain rate of the Newtonian viscosity increased with increasing temperature in accordance with the Arrhenius relation. The strain rate dependence of viscosity was described well with a master curve expressed by a stretched exponential function η/η 0 =1− exp (C/ e β ) . The Newtonian viscosity was successfully described with the free-volume model of Cohen and Grest. The fragility of the Newtonian viscosity revealed that the supercooled liquids of the metallic glasses were classified into the relatively strong liquids such as Ge 10 As 10 Se 80 , B 2 O 3 and Na 2 O–2SiO 2 glass formers.

RHEOLOGY OF Na-RICH MONTMORILLONITE SUSPENSION AS AFFECTED BY ELECTROLYTE CONCENTRATION AND SHEAR RATE

Abstract: Rheolo gical measurements were used to evaluate the particle-particle associations of Na-rich montmorillonite in suspensions, under various electrolyte concentrations. A 2% free electrolyte clay sus- pension showed pseudoplastic flow behavior and had a high apparent viscosity, attributed at low shear rates to the high volume fraction of the suspended clay platelets, the flexibility of the platelets, and the presence of edge-to-edge association. The breaking of edge-to-edge associations and the progressive orientation of the individual platelets in the direction of flow contribute to the reduction in viscosity with increasing shear rate. The compression of the diffuse double layer at a NaCI concentration of 10 mEq L -t contributes to the free movement of the individual platelets, even at low shear rates. The flow behavior changed from pseudoplastic to plastic at an NaCI concentration of 100 mEq L-L At this electrolyte concentration, face-to-face associations of specific junction points at certain areas of the planar surface are probably occurring. The apparent viscosity of the clay suspension for the two particle-size ranges (<2 and <0.02 p~m) at all shear rates converged to a minimum value of 4.5 mPa s at NaC1 concentrations of 10-20 mEq L-L On both sides of the minimum, the lower the shear rate, the greater the slope. The apparent viscosity of a 2% suspension of Na-rich montmorillonite <0.02 ~zm particles, however, was significantly greater than that observed for a suspension of <2 Ixm particles. This high apparent viscosity is attributed to the increase in edge surface area and the number of clay particles in a unit volume. We suggest that edge-to-edge association between Na-rich montmorillonite platelets prevails when the NaC1 concentration is below the electrolyte critical concentration, for which the apparent viscosity of the suspension is at its minimum value, whereas face-to-face association prevails at NaC1 concentrations above this critical value.

Rheological properties of selected light colored Jordanian honey

Abstract: The rheological properties of Apple, Besromia, Citrus, and Ziziphus types of light colored Jordanian honey were examined. The types of honey used were identified via assessing the source of nectar using pollen analysis (Melissopalynology). The moisture content of honey samples was indirectly assessed via measuring the refractive index of the sample using a refractometer. A rotational, concentric cylinder viscometer was used to measure rheological properties of honey samples. The apparent viscosity was measured as a function of the shear rate. In addition, the apparent viscosity was measured, at constant shear rate at 2.2 s−1, as a function of shearing time. Newton's law of viscosity was found to adequately describe the flow behavior of honey samples. The apparent viscosity was found to decrease with temperature, and the temperature dependency of viscosity was found to follow the Arrhenius model. Moreover, the viscosity was also found to decrease with moisture content of honey. An exponential fit was used ...

Micellar Synthesis and Properties of Hydrophobically Associating Polyampholytes

Abstract: Water-soluble polymers containing a small amount of hydrophobic groups have been prepared in aqueous medium by radical polymerization of acrylamide, two oppositely charged monomers (sodium 2-acrylamido-2-methylpropanesulfonate and [2-(methacryloyloxy)ethyl] trimethylammonium chloride) and a hydrophobic monomer (N,N-dihexylacrylamide or N-(4-ethylphenyl)acrylamide). The synthesis has been achieved by using a micellar process, in which the use of a surfactant ensures the solubilization of a hydrophobic monomer in aqueous solution. The rheological properties in aqueous solution depend on the amount and nature of the hydrophobes, the proportion of charged monomer units, the polymer concentration, and the addition of salt. In the semi-dilute regime, the hydrophobically modified low charge density polyampholytes show a very significant enhancement in the viscosity, even in high salinity media. Examination of the viscosity both as a function of shear rate and as a function of time (fixed shear rate) shows these solutions to have shear thinning, shear thickening and rheopectic behavior. Fluorescence measurements show the existence of hydrophobic domains even at high dilution. The aggregation is a gradual process without a distinct critical aggregation concentration.

Effect of the aeration rate on pullulan production and fermentation broth rheological properties in an airlift reactor

Abstract: The effect of aeration rate on pullulan production and the rheological properties of the fermentation broth in an airlift reactor was investigated. An airlift fermenter was shown to be an appropriate fermentation system for the production of pullulan. A maximum pullulan concentration (30 kg m−3), biomass concentration (6.0 kg m−3), pullulan yield (60%, w/w) and sugar utilization (100%, w/w) was obtained at an aeration rate of 2 vvm. The mycelium and the yeast-like cells were the morphological forms responsible for pullulan production. The highest polysaccharide concentration was obtained when the mycelial forms and the yeast-like cells were 60% and 40% (w/w) of the total biomass, respectively. The apparent viscosity of the broth was increased with the increase of the aeration rate from 1 to 2 vvm and then decreased at higher vvms. On the other hand, the dissolved oxygen concentration and the volumetric mass transfer coefficient continually increased with the increase of the aeration rate. The mycelial forms and the production of extracellular polysaccharide were responsible for the non-Newtonian flow behaviour of the fermentation broth. The rheological behaviour can be characterized by a power law type of equation. The relationship between shear rate/shear stress and shear rate/apparent viscosity showed a non-Newtonian behaviour of the fermentation broth. © 2001 Society of Chemical Industry

Hydroxyapatite Nano Sol Prepared via A Mechanochemical Route

Abstract: Well-dispersed sol with crystalline hydroxyapatite (HAp) was obtained directly by milling a mixture comprising Ca(OH)2, an aqueous solution of H3PO4 and a dispersant, an ammonium salt of polyacrylic acid. The average crystallite size of HAp was below 20 nm. Ca/P molar ratio of the product was 1.51 ± 0.04, i.e. Ca deficient from stoichiometric HAp. Minimum apparent viscosity was attained at a dispersant concentration 0.92wt% of sol. An as-milled sol was diluted by a factor 10–2.61 solid wt% to give a Newtonian fluid of 2 mPa s. From the diluted sol, we obtained a few μm thick dense film of HAp by dip coating on the slide glass precoated by chitosan.

Viscosity of gruels for infants: a comparison of measurement procedures

Abstract: Numerous studies have been carried out to investigate energy density and consistency of gruels for infants in developing countries. However, starch-rich gruels have a complex rheological behavior and their consistency is difficult to characterize. Many published gruel viscosity data are available, but the lack of standardized viscosity measurement procedures makes comparisons and interpretations difficult. The influences of viscometer type and viscosity measurement conditions on gruels prepared with simple or multicomponent flours were assessed in this study. The results showed a drastic decrease in apparent viscosity when the shear rate increased. Other factors like shear time and gruel temperature also had a marked influence on apparent viscosity. For two types of gruel (maize or multicomponent flour) prepared at different concentrations, correspondences between a short qualitative description of the consistency and apparent viscosity values obtained with several viscometers in different measurement conditions are given. Finally, recommendations are put forward on techniques to obtain valid data on gruel consistency, adapted to each type of study (laboratory, field or large-scale surveys).