Influence of Na~+/K~+ on Stability and Rheological Property of Silica Sol
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The influence of K+and Na+concentrations on the stability and rheological property of silica sol system have been studied by rheological method.The results show that the influences of K+ on the stability of silica sol is much larger than that of Na+.Under the low shearing rate,all discussing systems showed the typical disperse system of rheological properties,which is shear thinning.While under the high shearing rate,the resemble Newtonian fluid characteristics has been found.Keywords:
Shearing (physics)
Shear thinning
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A systematic investigation has been performed to relate the effect of glycerol composition to the rheological properties of aqueous suspensions of hydrophilic fumed silica at pH far from the isoelectric point. Steady state/dynamic rheology and electrophoresis measurements are compared to correlate the stability of the suspension with particle-particle and particle-solvent interactions. Although the extent of electrostatic stability is reduced by addition of glycerol, the rheological properties show a transition from a highly flocculated gel to stable dispersions containing no microstructures. This is attributed to a high degree of hydrogen-bonding between glycerol and the Aerosil surface silanol groups. Small dissociation of NaCl and particles reduce the effect of ion exchange and particle bridging mechanisms when the suspensions destabilise in the presence of glycerol. The high viscosity of glycerol is important with respect to the formation of a thick solvation layer around the particles. These parameters give rise to short-range, non-DLVO repulsive solvation forces, which stabilise the dispersion. At intermediate concentrations of glycerol (30–60 wt%) the apparent viscosity increase abruptly and irreversibly as both the extent and time of shearing are increased. The shear rate for the onset of the shear thickening is found to be retarded by decreasing the particle and salt concentration as well as by increasing the glycerol concentration. It is postulated that at intermediate glycerol concentration, where the height of the energy barrier is small, mechanical forces can activate the particles to overcome the energy barrier to enter the region where attractive forces dominate. Here, domination of the hydrodynamic forces to the colloidal forces under the shear results in formation of irreversible gels which does not relax to its initial condition.
Fumed silica
DLVO theory
Suspension
Particle (ecology)
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Water-soluble cellulose ethers are widely used as stabilizers, thickeners, and viscosity modifiers in many industries. Understanding rheological behavior of the polymers is of great significance to the effective control of their applications. In this work, a series of cyanoethylcellulose (CEC) samples with different molecular weights were prepared with cellulose and acrylonitrile in NaOH/urea aqueous solution under the homogeneous reaction. The rheological properties of water-soluble CECs as a function of concentration and molecular weight were investigated using shear viscosity and dynamic rheological measurements. Viscoelastic behaviors have been successfully described by the Carreau model, the Ostwald-de-Waele equation, and the Cox–Merz rule. The entanglement concentrations were determined to be 0.6, 0.85, and 1.5 wt% for CEC-11, CEC-7, and CEC-3, respectively. All of the solutions exhibited viscous behavior rather than a clear sol-gel transition in all tested concentrations. The heterogeneous nature of CEC in an aqueous solution was determined from the Cox–Merz rule due to the coexistence of single chain complexes and aggregates. In addition, the CEC aqueous solutions showed good thermal and time stability, and the transition with temperature was reversible.
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Shear thinning
Dilatant
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Silica fume
Hydrophobic silica
Shear thinning
Particle (ecology)
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Stability and rheological studies on gel emulsions (w/o high internal phase ratio emulsions, HIPRE) both with pure and commercial polyethyleneglycol alkyl ether surfactants are reported. Stability of gel emulsions at room temperature is increased by addition of NaCl to the internal phase; in contrast, no appreciable effect is found at higher temperatures. Rheological properties are influenced by both NaCl concentration and temperature. Apparent yield stress and elastic modulus are increased either by NaCl addition or temperature increase. Shear modulus as a function of volume fraction is analyzed in terms of droplet size and interfacial tension.
Volume fraction
Shear modulus
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Fumed silica
Suspension
Dilatant
Hydrophobic silica
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The rheological properties and microstructure of nanocrystalline cellulose (NCC) aqueous suspensions have been investigated at different concentrations. The suspension is isotropic up to 3 wt %, and phase separates to liquid crystalline and isotropic domains at higher concentrations where the samples exhibit a fingerprint texture and the viscosity profile shows a three-region behavior, typical of liquid crystals. The suspension behaves as a rheological gel at even higher concentrations where the viscosity profile shows a single shear thinning behavior over the whole range of shear rates investigated. The effects of ultrasound energy and temperature on the rheological properties and structure of these suspensions were studied using polarized optical microscopy and rheometry. Our results indicate that the amount of applied ultrasound energy affects the microstructure of the suspensions and the pitch of the chiral nematic domains. The viscosity profile is changed significantly at low shear rates, whereas the viscosity of biphasic suspensions at intermediate and high shear rates decreased with increasing temperature. This suggests that, between 30 and 40 °C, structural rearrangement takes place. At higher concentrations of about 10 wt %, the temperature has no significant effect on viscosity; however, a marked increase in viscosity has been observed at around 50 °C. Finally, the Cox–Merz rule was found to fail after a critical concentration, thereby implying significant structural formation. This critical concentration is much higher for sonicated compared to unsonicated suspensions.
Rheometry
Nanocrystalline material
Shear thinning
Suspension
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Shear thinning
Dilatant
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1-Butyl-3-methylimidazolium tetrafluoroborate was synthesised. The effect of concentration,tremperature and frequency on the rheological and viscoelastic properties of dispersions of silica in[BMIm]BF4 have been studied. The result showed that the system shows reversible shear thickening behavior. Under steady shear test,as the SiO2 concentration increasing and the temperature decreasing,the shear thickening phenomena are more obvious. Under oscillation shear test,the magnitude of loss modulus G″ is larger than that of storage modulus G',which shows that these suspensions mainly possess viscous property. As the SiO2 concentration,angular frequency increasing and the temperature decreasing,G' and G″ increase. [BMIm]BF4 as dispersion medium has a stronger thickening effect than PEG400 as dispersion medium.
Dilatant
Tetrafluoroborate
Shear modulus
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