Rheological Properties Of Aqueous Dispersions Research Articles

Techno-functional properties of gluten-free pasta from hyperprotein quinoa flour

Many consumers who are aware of the importance of good nutrition demand quality food alternatives. In particular, many of them are looking for quality, plant-based protein sources such as quinoa. The objective of this work was to evaluate the techno-functional properties of gluten-free pasta from hyperprotein quinoa flour. Pasta mixes were made from gluten-free flours, corn, rice, cassava starch, hyperprotein quinoa flour and defatted high protein quinoa flour, which were subsequently extruded. The flow rheological properties of aqueous dispersions of flour mixtures were analyzed before and after the pasting test. In addition, thermal properties were analyzed by differential scanning calorimetry and structural properties by Fourier transform infrared spectroscopy. The results showed a change of flow from dilatant (n > 1) to pseudoplastic (n < 1) after the pasting test. In addition, a positive correlation was observed between hyperprotein defatted quinoa flour and viscosity, and a negative correlation with hyperprotein quinoa flour. Regarding thermal properties, it was found that all blends showed low gelatinization enthalpy values, attributed to the high proportions of HQF and HDQF. Spectroscopic analysis showed that the extrusion did not significantly affect the native structure of the protein, by monitoring the intensities of the 1648 cm−1, 1656 cm−1 and 1667 cm−1 bands associated with the Random coil, α-helix, β-turns secondary structures, respectively. It was possible to conclude that both hyperprotein quinoa flour and defatted hyperprotein quinoa flours have a differential influence on the techno-functional properties of pasta. The first one, tends to reduce viscosity and consistency while the second one tends to increase it. Finally, moderate temperatures during extrusion did not cause significant changes in starch and protein structures as determined by spectroscopic study.

Use of Dynamic Shear Rheology to Understand Soy Protein Dispersion Properties.

Soy flour dispersions are used as adhesives for bonding interior wood laminates, but the high viscosity of these dispersions requires low solids in the adhesive formulations; the greater water content causes excessive steam pressure during hot press manufacturing. This limits the utility of soy adhesives in replacing urea-formaldehyde adhesives; thus, understanding the cause of high soy viscosities is important. Lack of literature on aqueous soy flour dispersion rheology led to our dynamic rheology studies of these dispersions to understand high viscosity and the effect of various additives. Even at low soy solids, the elastic nature outweighs the viscous properties at low shear, although increasing the shear results in shear-thinning behavior after the yield point. At even higher shear, beyond the flow point where the storage and loss moduli cross, some of the dispersions show an additional shear thinning transition. The comparison of the rheological properties of aqueous dispersions of the soy flour and protein isolate, and another natural protein, ovalbumin from egg whites, led to a better understanding of different types of rheological behaviors. The experimental observations of two observed shear thinning events for soy are consistent with the model of dispersed particles, forming clusters that then form large scale flocculants.

DEVELOPMENT OF COMPETITIVE DRILLING FLUIDS FOR HORIZONTAL DIRECTED DRILLING BASED ON BENTONITE OF CHERKASKY DEPOSIT

Taking into account the need for the post-war reconstruction of the country’s infrastructure, the development of high-quality drilling fluids based on Ukrainian mineral raw materials becomes a particularly urgent problem. Detailed studies of the rheological properties of aqueous dispersions of Na+-bentonite from the Cherkasky deposit (Ukraine) were carried out in relation to the development of drilling fluids for horizontal directional drilling. The effect of pH, ionic strength, concentration of the solid phase, alkaline reagent (Na2CO3) and polymer additives (PAC and PAA) on the rheological properties of Na+-bentonite dispersions was studied, and the most important correlations between the specified parameters and the performance characteristics of ready-made drilling fluids for horizontal directional drilling were obtained. A new, more effective PAA polymer is proposed to improve the viscosity-speed characteristics and other indicators of drilling fluids instead of the scarce imported PAC-polymer, and its optimal concentration is determined. It was established that with the introduction of small additives (0.005–0.025 %) of PAA polymer, drilling fluid based on Cherkasky Na+-bentonite in all its rheological characteristics is not inferior to imported analogues. The joint analysis of the obtained dependencies allowed to develop the optimal technology for obtaining bentonite gel and drilling fluids based on it, the indicators of which meet the requirements of the horizontal directional drilling. Based on the results of comparative studies of the rheological properties of drilling fluids in a wide range of deformation rates (0–1312 s–1), the competitiveness of the new drilling fluids has been proven on par with the best foreign analogues. Bibl. 17, Fig. 10, Tab. 4.

Rheological Properties of Aqueous Dispersions of Bacterial Cellulose

Bacterial cellulose as polysaccharide possessing outstanding chemical purity and a unique structure compared with wood cellulose, attracts great attention as a hydrocolloid system. It was shown, that at intense mechanical action on a neat bacterial cellulose film in presence of water, the gel-like dispersions are obtained. They retain stability in time (at least, up to several months) and temperature (at least, up to 60 °C) without macro-phase separation on aqueous and cellulose phases. The main indicator of the stability is constant viscosity values in time, as well as fulfilling the Arrhenius dependence for temperature dependence of viscosity. Flow curves of diluted dispersions (BC content less than 1.23%) show strong non-Newtonian behavior over the entire range of shear rates. It is similar with dispersions of micro- and nanocrystalline cellulose, but the absolute viscosity value is much higher in the case of BC due to more long fibrils forming more dense entanglements network than in other cases. Measuring the viscosity in increase and decrease shear rate modes indicate an existence of hysteresis loop, i.e., thixotropic behavior with time lag for recovering the structural network. MCC and NCC dispersions even at cellulose content more than 5% do not demonstrate such behavior. According to oscillatory measurements, viscoelastic behavior of dispersions corresponds to gel-like systems with almost total independence of moduli on frequency and essentially higher values of the storage modulus compared with the loss modulus.

Rheological Properties of Aqueous Dispersions of Xanthan Gum Containing Different Chloride Salts Are Impacted by both Sizes and Net Electric Charges of the Cations

Xanthan gum (XG) is one of the most effective thickener agents used worldwide. In foods products, one of the factors affecting its physical properties is the ionic strength of the medium. Though it is well known that XG rheological properties in aqueous media depend on both type and concentration of electrolytes, correlations between such dispersion properties and molecular aspects of dispersed XG chains are still to be more deeply studied. Thus, in the present study, aqueous XG dispersions [200 mg⋅(100 mL)−1] added of Na, K, Mg or Ca chlorides (ionic strength 50 mM or 100 mM) were rheologically characterized, and the corresponding results were explained based on different physicochemical analyses. Comparing to the control (unsalted XG dispersion), KCl and CaCl2 tended to produce a more drastic decrease of apparent viscosities of XG dispersions than NaCl and MgCl2. In dynamic-oscillatory assays, the predominance of elastic character over viscous character was more evident for XG dispersions containing KCl and CaCl2, in particular at frequencies > 0.1 Hz. XG dispersions containing KCl or CaCl2 also presented smaller pH and |ζ-potentials| values, as well as greater densities and average hydrodynamic diameters of dispersed XG chains, when compared to respective counterparts containing NaCl or MgCl2. As the decreasing order of the cations radii is K+ > Ca2+ ≈ Na+ > Mg2+, our results allowed deducing that not only the net electric charges of the cations, but also their sizes, should be considered when analyzing the effect of chloride salts on rheological properties of XG aqueous dispersions, according to the desired for this hydrocolloid (weak thickener, strong thickener or pro-gelling agent).

High-pressure induced thermo-viscoelasticity and dynamic rheology of gum Arabic and chitosan aqueous dispersions

Effect of high pressure treatment (200 MPa, 400 MPa, 600 MPa) on rheological properties of aqueous dispersions of gum Arabic (6 g/100 g, 15 g/100 g, and 20 g/100 g) and chitosan (2 g/100 g, 4 g/100 g) was studied. Dynamic properties were assessed using an angular frequency range of 1–25 rad s−1. Flow properties were measured by applying a programmed shear rate of 0.1–100 s−1 for 10 min (upward) and 100–0.1 s−1 for the next 10 min (downward). A power law shift function was used to describe the deviations from the Cox-Merz theory in all samples. Thermo-viscoelasticity was evaluated using a programmed heat/hold/cool cycle (22 °C/70 °C/20 °C). Two term-exponential and a Gaussian model well fitted the thermo-viscoelastic behavior of both gums. The thermal compatibility, regarding a logarithmic phase shift of loss tangent ratios, was also studied. Results showed higher incompatibilities at lower temperatures, while the shift phases tended to zero at higher temperatures. Overall, HP treatment intensified the existence of a stronger and temperature sensitive hydrocolloid network for 4 g/100 g chitosan and 20 g/100 g GA. The highest incompatibility was seen in 20 g/100 g gum Arabic which was a 1–1.5 order of magnitude.

Effect of Ethonium Adsorption on Structure Formation in Nanosilica Dispersions

Adsorption of ethonium on silica surface strongly affects the particle size distribution, stability and rheological properties of aqueous dispersions of fumed silica. The Sshape of isotherm of ethonium adsorption on nanosilica suggests the multilayer adsorption. The adsorption of ethonium leads to changes in the shape of the pHdependence of the zeta-potential and a significant increase in the particle sizes in the aqueous dispersions of silica. A marked increase in the colloidal stability is observed for the dispersions at silica concentration of 5 wt.%, while for 1 wt.% dispersions the ethonium presence almost does not affect the stability. The rheological properties of the dispersions depend on the ethonium concentration, and the maximum values of the viscosity and rheopectic behavior are observed at ethonium concentration of 0.1-0.3 wt.%

Influence of Indifferent Electrolytes on Formation of Coagulative Structures in Aqueous Silica Dispersions

Effects of indifferent electrolytes (NaCl, KCl, LiCl, NaI, NaNO3, CaCl2, and MgCl2) on the electrical double layer (EDL), aggregation, gelling, and rheological properties of aqueous dispersions of nanosilica were investigated. All examined indifferent electrolytes enhance interactions between nanoparticles of fumed silica through the coagulation mechanism. The critical concentration of gelation and gelling time decrease in the presence of the electrolytes, while the effective viscosity of the dispersions and average size of aggregates (Def) increase in series of chlorides: Li+ &lt; Na+ &lt; K+ &lt; Ca2+ &lt; Mg2+. That corresponds to an increase in the cation radius and reduction of the hydration shell. The nature of anions and cations significantly affects the values of Def and viscosity. For sodium salts, the viscosity increases in series I- &lt; NO3- &lt; Cl- corresponding to an increase in the hydration shell.

The Particle Size and Shape of Polyaniline in Aqueous Solutions of Poly-(N-Vinylpyrrolidone)

Certain rheological properties of aqueous dispersions of polyaniline in the presence of poly-(N-vinylpyrrolidone) as a stabiliser were investigated. The influence of the molecular weight of poly-(N-vinylpyrrolidone) and also the concentration of aniline and ammonium peroxydisulphate on the size and shape of the polyaniline particles was shown.

Effect of amylopectin on the rheological properties of aqueous dispersions of starch–sodium palmitate complexes

Aqueous dispersions of normal and high-amylose corn starch were steam jet cooked and blended with aqueous solutions of sodium palmitate to give starch containing amylose–sodium palmitate inclusion complexes. Partial conversion of complexed sodium palmitate to palmitic acid by addition of acetic acid led to the formation of gels. Blends of inclusion complexes prepared from normal and high-amylose corn starch were used to vary the amylose:amylopectin ratio of the gels, and the linear viscoelastic moduli were found to decrease with decreasing amylose:amylopectin ratio. Precipitation of the complexed starch at low pH showed that most of the amylopectin was not part of the gel network. The elastic modulus of the gels was shown to decrease sharply between 74 and 85°C, and the transition temperature increased strongly with decreasing amylose:amylopectin ratio.

Influence of pH and temperature on the rheological properties of aqueous dispersions of starch–sodium palmitate complexes

Abstract Aqueous dispersions of high-amylose corn starch were steam jet cooked and blended with aqueous solutions of sodium palmitate to form amylose inclusion complexes. The rheology of dispersions of these complexes was examined. Acetic acid was added to reduce the pH, converting complexed sodium palmitate to palmitic acid. Associations of the complexed palmitic acid and reduced electrostatic repulsion resulted in a sharp increase in the linear viscoelastic properties of the materials. Further reduction of the pH led to precipitation of palmitic acid complexes and a decrease in the gel strength. Temperature ramps showed a sharp, reversible decrease in the elastic modulus. The temperature at which this decrease occurred depended on both the concentration and pH.

Comparative study between the viscoelastic behaviors of different lipid nanoparticle formulations

Application of drug substances to the skin for systemic absorption or action in a particular layer of the skin is a rather old approach. However, over the last years it has received much more attention, as a consequence of the development of new membrane-moderated and matrix reservoir devices. As new reservoir systems, solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) have been successfully tested for dermal application of different physicochemical substances. The knowledge obtained from rheological investigations of these systems may be highly useful for the characterization of the newly developed topical formulation. In the present study, an oscillation frequency sweep test was used for the evaluation of storage modulus (G'), loss modulus (G''), and complex viscosity (eta*) of twelve different SLN and NLC formulations, over a frequency range from 0 to 10 Hz. The lipidic aqueous dispersions were prepared using three different solid lipids (Softisan138, Compritol888, and stearyl alcohol) as matrix material. Miglyol812, tocopherol, sunflower oil, and long-chain triacylglycerols were the chosen liquid lipids for NLC preparation. The objective of the present work was to investigate the effect of these different liquid lipids on the rheological properties of aqueous dispersions of NLC as model systems. It was found that the liquid oil component of the formulation has a strong influence on the viscoelastic parameters, which are dependent on the particle size, zeta potential, and crystallinity of the lipid particles, as well as on the solid lipid used.

Exopolysaccharide production by Streptococcus thermophilus SY: production and preliminary characterization of the polymer.

To evaluate the effect of yeast extract (YE) concentration, temperature and pH on growth and exopolysaccharide (EPS) production in a whey-based medium by Streptococcus thermophilus SY and to characterize the partially purified EPS. Factorial experiments and empirical model building were used to optimize fermentation conditions and the chemical composition, average molecular weight (MW) and rheological properties of aqueous dispersions of the EPS were determined. Exopolysaccharide production was growth associated and was higher (152 mg l(-1)) at pH 6.4 and 36 degrees C with 4 g l(-1) YE. High performance size exclusion chromatography of the partially purified EPS showed two peaks, with a weight average MW of 2 x 10(6) and 5 x 10(4), respectively. The EPS was a heteropolysaccharide, with a glucose : galactose : rhamnose ratio of 2 : 4.5 : 1. Its water dispersions had a pseudoplastic behaviour and showed a higher viscosity of xanthan solutions. The fermentation conditions and some properties of an EPS produced by Strep. thermophilus, a dairy starter organism, were described.

“Weak Gel”-Type Rheological Properties of Aqueous Dispersions of Nonaggregated κ-Carrageenan Helices

The rheological properties of kappa-carrageenan helices dispersed in an aqueous medium, which prevents aggregation of helices, were investigated. A dispersion of 1.5% w/w nonaggregated kappa-carrageenan helices exhibited gel-like dynamic mechanical spectra at 20 degrees C; that is, the storage modulus G' predominated over the loss modulus G' ' in the entire frequency range examined (0.5-100 rad/s). However, the observed slight frequency dependence of the moduli and the relatively large value of tan delta (= G' '/G' > 0.1) were typical of so-called weak gels. The magnitude of G' of the kappa-carrageenan weak gels was less than that of conventional gels formed by 0.15% w/w kappa-carrageenan in an aggregating condition at 20 degrees C. Under large deformation, enough for the conventional gels to rupture, the weak gel systems flowed but never ruptured, suggesting that the weak gel-type rheological properties of the kappa-carrageenan dispersions were due to a sufficiently long relaxation time of topological entanglements among double-helical conformers but not due to the formation of a three-dimensionally percolated permanent network.

Intersupplier and interlot variability in hydroxypropyl celluloses: implications for theophylline release from matrix tablets

The physical and physicochemical properties of three lots of high-viscosity hydroxypropylcellulose (HPC) (two lots from a Japanese supplier and one lot from a US supplier) were compared. The drug-release properties of theophylline matrix tablets prepared with the different polymers were also investigated. HPCs from the two suppliers showed clear differences in molecular weight, molecular structure, particle size distribution, particle shape, and water affinity. Furthermore, clear differences were observed in the time-course of drug release from tablets made with the different polymers. The differences in basic physical and physicochemical properties of the HPCs affect compression behaviour, the capacity for and time-course of water uptake, and the rheological properties of aqueous dispersions, which explains the observed differences in time-course of drug release. Molecular weight and particle size distribution are particularly important determinants of drug release properties. Abnormally rapid drug release was observed from tablets prepared with relatively small amounts of the highest-molecular-weight highest-particle-size HPC. This result, together with the fact that the time-course of drug release differs markedly between matrix tablets prepared with HPCs that come from different suppliers but that are nominally interchangeable (at least according to the criteria given in the US Pharmacopoeia), suggests that these two properties (mean molecular weight and particle size distribution) are of value for quality control of HPCs destined for use in the manufacture of matrix tablets.

Unusual Thixotropic Properties of Aqueous Dispersions of Laponite RD

The rheological properties of aqueous dispersions of the synthetic hectorite clay Laponite RD that form gel-like structures have been investigated. Special emphasis has been laid on the phenomenon of thixotropy. Structural recovery at rest after steady shear is considered a fundamental thixotropic process and has been characterized by small amplitude oscillatory shear measurements. A special sealing technique was used to prevent the evaporation of water during these experiments. After cessation of steady shear |η*| increases monotonically with time and even after 16 days no equilibrium viscosity value is reached. A single power law |η*| ∼tnholds within the time regime from 10 to 106s. The exponentn= 0.13 ± 0.02 is independent of clay concentration and mechanical pre-treatment of the material. This type of kinetics has not been reported so far for the thixotropic recovery of any clay dispersion and it does not fit the common definition of thixotropy. The reorganization of the gel structure determining this thixotropic phenomenon is interpreted as a cooperative self delaying process similar to the aging of glassy polymers or precipitation from supersaturated solid solutions.

Rheology and Microstructure of Succinylated Canola Protein Isolate

ABSTRACTSteady shear rheological properties of aqueous dispersions of unmodified and succinylated canola (rapeseed) protein (54 and 84% modification of free amino groups) were examined over a wide range of pH (3.5–11.0) and NaCl concentration (0.0–0.70M). All dispersions were pseudoplastic and followed power‐law or power‐law plastic flow behavior. Apparent viscosity at shear rates of 10 and 1000 s‐1 was affected by extent of succinylation, pH, NaCl concentration, and interactions among these factors. At both shear rates, protein solubility and hydrophobicity were reliable predictors of apparent viscosity. Dispersion microstructure, as revealed by light microscopy, appeared to play an important role in flow behavior.

Colloidal properties of synthetic hectorite clay dispersions: I. Rheology

The rheological properties of aqueous dispersions of Laponite-RD—a synthetic hectorite-type swelling clay—have been studied at low ionic strength ([Na] ∼ 10 −3 mole dm −3) with a Weissenberg rheogoniometer. From measurements made under oscillatory shear, the storage, G′, and loss, G″, moduli have been determined in the concentration range 0.03 to 0.10 g ml −1. All these dispersions formed elastic gels on prolonged standing, and the progress and mechanism of gelation has been investigated by kinetic measurements of G′ at different temperatures. It is concluded that the development of elastic behavior which occurs during the gelation process, arises from osmotic swelling and the formation of an equilibrium structure due to electrostatic repulsion between the individual clay microcrystals.

Rheological properties of hydrolyzed polyacrylonitrile-grafted cellulose

The rheological properties of aqueous dispersions of hydrolyzed polyacrylonitrile-grafted cellulose (H-CPAN) have been investigated. The experimental results are consistent with the idea that the elementary particle is a rigid cellulose protofibril stabilized in suspension by associated polyelectrolyte side chains (polyacrylamide–polyacrylic acid copolymer grafts). The behavior of intrinsic viscosity with electrolyte concentration, the concentration depependence and shear dependence of the viscosity and of the steady-state and dynamic shear moduli are qualitatively explained on this basis.