Rheological Behavior Of Dispersions Research Articles

Influence of organic acids on the viscosity and rheological behavior of guar gum solution

The present study aims to determine the influence of four edible organic acids (ascorbic, citric, malic, and tartaric) at two concentrations (0.5, and 1 %) on the viscosity and rheological behavior of guar gum dispersion (0.2 %, w/v). The finding of this study revealed that the apparent viscosity of guar gum dispersions reduced when the shear rate increased. Additionally, the apparent viscosity of the guar gum dispersions reduced as the organic acids concentration increased from 0 to 1 %. The highest decrease in viscosity was related to 1 % ascorbic acid and the lowest was related to 0.5 % malic acid. The rheological behavior of dispersions were successfully modeled using Power law, Bingham, Herschel-Bulkley, and Casson models, and the Power law model was the best one for describing the behavior of guar gum dispersions containing organic acids. The Power law model showed good performance with the maximum r-value (mean = 0.9988) and least sum of squared error (SSE) values (mean = 0.0021) and root mean square error (RMSE) values (mean = 0.0119) for all samples. The consistency coefficient (k-value) values of the samples (Power law and Herschel-Bulkley models) reduced as the acid percent was increased. The sample containing 1 % tartaric acid had the lowest k-value and the sample containing 0.5 % ascorbic acid had the highest k-value. The flow behavior index (n-value) (Power law and Herschel-Bulkley models) of the samples increased when the acid percent was increased. In summary, the use of guar gum in food products containing high concentrations of tartaric and ascorbic acids is not recommended.

A Comprehensive Physical Profile for Aqueous Dispersions of Carbon Derivatives as Solar Working Fluids

The application of nanofluids in direct solar absorption, heat transfer or direct solar steam generation entails carrying out a comprehensive study taking into account several physical quantities. Long-term stability, rheological, thermophysical and optical properties of dispersions must be known to assess their potential for envisaged applications. Two low-concentration nanofluids, 0.005 and 0.05 wt%, of sulfonic acid-functionalized and polycarboxylate chemically modified graphene nanoplatelets in water were considered in this work. Elemental analyses of the nanopowders and pH evaluations of the colloids were carried out. The rheological behaviour of dispersions at different temperatures was studied by rotational rheometry. Thermal conductivities were measured by the transient hot wire method and densities by the oscillating U-tube technique. Additionally, a brief report of the optical properties was included to provide a comprehensive physical analysis.

Formation of Arrested States in Natural Di- and Trioctahedral Smectite Dispersions Compared to Those in Synthetic Hectorite — A Macro- and Microrheological Study

AbstractThe effect of natural clay-mineral properties on the rheological behavior of dispersion is very important in new geotechnical and industrial applications. The colloidal behavior of natural clay minerals with various octahedral structures was investigated using macro- and microrheological measurements and compared with the behavior of synthetic hectorite. In the present study montmorillonite (dioctahedral smectite of Volclay), natural hectorite (trioctahedral smectite of SHCa-1 Source Clay), and the synthetic trioctahedral smectite Laponite®, with lateral layer dimensions of 277, 100, and 30 nm, respectively, were used. The structure formation, kinetics of aging, and broad bandwidth viscoelastic response (10-2 — 106 rad/s) of their dispersions were obtained using mechanical shear and squeeze flow rheometry combined with diffusing wave spectroscopy (DWS) and multiple particle tracking (MPT) microrheology. State diagrams were determined at inherent pH considering the clay-mineral and NaCl concentrations as well as the kinetics of structure formation and sample aging. Due to the larger mean layer diameter and greater layer-charge density of natural clay-minerals, their sol—gel transitions occurred at higher solid and NaCl concentrations than those of Laponite®. Structure formation was faster at pH < pHPZC,edge than at pH > pHPZC,edge (point of zero charge at the edge). The long-term aging of natural clay-mineral samples was less pronounced in the glass state than in the gel state, in contrast to the findings for Laponite®. The storage modulus, G’, of clay-mineral dispersions in arrested states remained essentially constant in a wide frequency range (up to 100 rad/s), as expected. The corresponding plateau value of G’ depends on the number of particle contacts per volume and, hence, increased with decreasing particle size at a given concentration. The dissipation mechanisms determining the high-frequency loss modulus, G", however, are independent of particle size and, accordingly, the high-frequency crossover of G’ and G" shifted to higher values when the particle size decreased. The MPT data revealed structural refinement on the submicrometer length scale during the aging of weak hectorite gels, which was similar to the results for Laponite®. No refinement, however, occurred for montmorillonite in the glass or strong gel state.

Rheological study of concentrated dispersions. Application to the drilling fluid.

In order to understand the rheological behavior of concentrated aqueous Algerian bentonite dispersions of drilling (sodium bentonite of Mostaganem “m’zila”), rheological tests were carried out. By varying the concentration of bentonite, flow tests have allowed to estimate the yield stress and apparent viscosity for each concentration and to see their influence on the rheological behavior of these dispersions. In addition dynamic tests (oscillatory) are used to define the linear region of our samples, the state of our fluid (elastic solid or viscous liquid) and understanding the mechanisms of structuring of the particles constituting the material. In parallel, other tests coupled with rheological measurements such as x-rays diffraction to know the mineralogical composition and granulometry to estimate the bentonite particle size.

The degree of protein aggregation in whey protein isolate-based dispersions modifies their surface and rheological properties

ABSTRACTThis work aims to study the effect of degree of protein aggregation on the surface and rheological properties of whey protein isolate dispersions with different concentrations (80, 100 and 120 g/kg), pHs (5.5 or 6.5) or NaCl contents (1 or 2 g/kg). Dispersions were thermally treated at 70, 75 and 80°C for different times. By mixing aggregated with native protein dispersions, different degrees of aggregation (0%, 20%, 40%, 60% and 80%) were obtained. Surface tension of the dispersions was determined by the pendant drop method, whilst their rheological properties were obtained from flow curve tests. A slight effect of the degree of aggregation over diffusion was found, which indicates that native proteins dominated the decrease in surface tension. The rheological behavior of dispersions with NaCl addition changed from Newtonian to shear thinning for aggregation degrees above 20%, whilst all dispersions at pH 5.5 and 6.5 presented a shear thinning behavior.

Improvement of Rheological Properties of Little Noble Varieties from Boa Vista Bentonites - Part I: Experimental Design

The noble variety of the Boa Vista bentonites became scarce, originating fluids which do not answer the Petrobras specifications. The utilization of a blending with available samples have been used in industry successfully. Thus, the present work aims to use the mixture modeling methodology with design in simplex-centroid network and further purification by hydrocycloning, trying to optimize rheological properties of dispersions prepared with little noble clays, obtaining drilling fluids that attend the normative requirements. Initially, the rheological behavior of dispersions on each of the five clays, activating them in proportions of 50, 75, 100, 125 e 150 meq of Na2CO3/100 g of dry clay. After result analyzing, the mixtures were formulated, using experimental planning with the five clays, but with activation in proportions of 100 and 125 meq of Na2CO3/100 g of dry clay.

Aqueous dispersions of gelled collagen particles. Part 1: experimental characterization of stiffness and rheological properties

PurposeTo study the rheological behavior of aqueous dispersions of collagen gelled media and to bring it into relation with the gel stiffness and microstructure.Design/methodology/approachCollagen gelled media were prepared at different concentrations and their stiffness was measured with dynamic elastic modulus (DEM) technique. The gelled media were reduced into dispersions of micelles and gel liquid phase and the apparent viscosity of these systems was investigated as a function of the gap thickness, the shear rate and the collagen concentration. The gap thickness was varied between 20 and 200 μm. The microstructure of the broken gelled media was finally explored with optical microscopy.FindingsDEM analysis has given values of the collagen gel stiffness ranging between 3 × 10−4 and 3.3 × 10−3 MPa. It has been shown that apparent viscosity grows with the increase of the gap thickness from 2 to 5 Pa s at constant collagen concentration and applied shear rate (4 percent, 100 s−1). A rise in the collagen concentration has produced an increase in the apparent viscosity of gelled media dispersions. Nevertheless, the phenomenological law does not obey previously proposed equations but follows a sigmoid modal. Shear‐thinning phenomenon has been observed when the shear rate is varied between 10 and 2,000 s−1.Research limitations/implicationsThe gel breaking process, which may cause changes in the microstructure of the micelles and hence in the rheological behavior of the dispersions, should be characterized measuring the forces acting on the samples during the rupture.Originality/valueThe paper provides useful information on the rheological behavior of aqueous dispersions of collagen gelled media.

Rheological Behavior of Aqueous Polyurethane Dispersions: Effects of Solid Content, Degree of Neutralization, Chain Extension, and Temperature

Rheological behavior of waterborne polyurethane dispersions was investigated with small-amplitude oscillatory shear flow experiments over wide ranges of concentration, degree of neutralization, chain extension, and temperatures to accelerate efforts to understand their film formation characteristics. The rheological properties of these environmentally friendly dispersions were found to be dependent on composition and degree of postneutralization. But the chain extension and degree of preneutralization were observed to have little effect on the rheological behavior of the dispersions at a constant polyurethane (PU) concentration. The complex viscosity of the polyurethane dispersions increased dramatically at a critical concentration of polyurethane (φ = 0.43), below which the viscosity increased slightly with composition. At this critical concentration the particles are crowded, and the observed viscosity increase is ascribed to the hydrodynamic interaction between the different particles. Furthermore, both G‘ ‘ and G‘ ‘ are strongly increased with increasing PU wt % in the dispersions (i.e., the higher the concentration of PU, the higher the values of G‘ and G‘ ‘). At 46 wt % PU the values of G‘ and G‘ ‘ are no longer frequency dependent, and G‘ is almost 1 order of magnitude higher than G‘ ‘, indicating formation of a fractal-type gel. The viscoelastic material functions were well described by simple power law equations and a Maxwellian (Hookean) model with 2−3 relaxation modes based on PU concentration and degrees of postneutralization at 30 °C. Time−temperature superposition of the dynamic moduli was good at temperatures and PU concentrations below that of the critical gel, and the temperature dependence of the shift factors conformed well to predictions from an Arrhenius-type relation, enabling calculation of the flow activation energy of 45 kJ mol-1 for the PUDs. As expected, time−temperature superposition failed to represent the behavior of the PUDs near the critical gel point. While the results of this study indicate a number of similarities to critical gelling systems, observed deviations from the viscoelastic behavior of Brownian suspensions of hard spheres were obtained, indicating that a more complicated theory that explicitly takes the intrinsic interactions, concentrations, and size distributions of the PU particles into account may be necessary for a more accurate quantitative description of these special model PUDs with enhanced benefits.

Effect of polymer bridging on rheological properties of dispersions of charged silica particles in the presence of low-molecular-weight physically adsorbed poly(ethylene oxide)

The effect of a low-molecular-weight physically adsorbed poly(ethylene oxide) on the rheological behavior of aqueous dispersions of silica particles (as a model system) has been investigated. Particular attention is given to the evolution of the rheological behavior with increasing polymer concentration in the system at different volume fractions of the particles. Experiments were performed in the absence of salt and just the pH of the dispersion was adjusted to 9.5, a condition at which the system is electrostatically stable and electrostatic repulsive forces are long range in nature. It was observed that the shear viscosity and the linear viscoelastic functions of the dispersion at 55 vol% increase initially through the addition of polymer, reach a maximum, and then decrease to a minimum with further addition of polymer to the system. At higher polymer concentrations, there may be an increase in the viscosity of the dispersion owing to an increase in the concentration of free polymer chains in the medium causing depletion flocculation in the system. The increase in the rheological behavior of the dispersion at low polymer coverage is attributed to polymer bridging flocculation caused by a low-molecular-weight poly(ethylene oxide) in the system. Comparison of the data given here with the results of earlier studies on the viscosity behavior of the system in the presence of salt (0.01 M) indicates that the range of the electrostatic repulsion has a significant role in the rheological behavior of the system.

Rheological study of dispersions prepared with modified soybean protein isolates

AbstractStructural modifications of modified soy protein isolates (SPI) were distinguished by rheological behavior. SPI were prepared by acidic (pH 2.5) and thermal‐acidic treatment without (pH 1.6) and with neutralization (pH 8.0). Dynamic properties of dispersions were determined through the variation of storage and loss moduli with frequency, and loss tangent behavior was analyzed. Changes in viscoelastic parameters with protein concentration (10–12% wt/vol) and time of heating (15–60 min) were also determined. Flow properties of dispersions were estimated through apparent viscosity and flow and consistency index measurements. Rheological behavior of dispersions was compared with those found by experiment with commercial mayonnaise, mustard, and salad dressing. The analysis of rheological parameters showed that thermally treated isolates formed dispersions with high elastic modulus and consistency index with a structure mainly stabilized by hydrophobic interactions, although no gelation process after cooling was observed. From the rheological point of view, it was deduced that thermally treated isolates could be used as ingredients in the formulation of salad dressings. The alkaline sample would be more versatile because, depending on protein concentration and thermal treatment, the consistency of its dispersions was like that in salad dressing, or similar to those of mustard and mayonnaise.

Crystal morphology of organic pigments and rheology of dispersions in ink and paint media

The purpose of this work is to establish relationships between physico-chemical character of pigments and rheological behaviour of dispersions under steady shear conditions. It has been found that the approximately cube-shaped crystals of CI Pigment Yellow 13-type pigments disperse substantially as individual crystals in (highly viscous) lithographic ink media; strength of structure and plastic viscosity relate simply to number concentration of crystals and area of the pigment/medium interface, respectively. Interpretation of data for dispersions of Red 57.1 pigments in similar media is complicated by persistent face-to-face aggregation of their rectangular plate-shaped crystals. In dispersions of metal-free monoazo pigments (Yellows 1 and 74, Reds 3 and 112) in decorative paint media (relatively low viscosity) strength of structure shows a markedly increased dependence on pigment concentration above a critical concentration. This concentration is different for each pigment and is determined primarily by crystal shape, the less cube-shaped the crystals the lower the critical concentration. Plastic viscosity is dependent upon area of the pigment/medium interface and thickness of adsorbed layer of paint medium.