The Detection of the Effect of Viscosity Growth in Nanodisperse Systems during Their Shearing with Ultralow Rates
N. B. Ur’ev, Yu. S. Svistunov, A. N. Potapov, and V. A. Starikov
Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
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Received March 12, 2008
Abstract — With a precision Haake RS1 rheometer, it is first found that at extremely low rates of shear (
10
3 to 10–4 s–1 or lower), in nanodisperse systems based on highly dispersed aerosil or aerosil–bentonite compositions, with an increase in the shear rate, a non-Newtonian flow is observed. It is accompanied with a continuous growth of the effective viscosity of the dispersions 
eff, till the yield point P 
Pk is reached. At P 
Pk, the effective viscosity decreases abruptly; the structure decomposes via an aggregate mechanism. Earlier it was believed, that each viscosity level there corresponds to a combination of the full destruction of structural bonds and their partial restoring up to the equilibrium level determined by eff. In addition, the structured dispersed system flow remains Newtonian unless the static yield point has been overcome; it corresponds to the largest viscosity of a virtually undestructed system. Using a special procedure, SEM-imaging of the structure of the bentonite-suspension, as well as the bentonite added with minor amounts of aerosil, was carried out in waterethanol medium. Photomicrographs of structure of the studied nanodisperse systems subject to shearing were obtained. The active filler (aerosil) particles distribution in the model system structure is studied. A procedure of studying the thixotropic properties of the structured nanodisperse systems in dynamic conditions is developed. The complex modeling of the structured nanodisperse system spreading over the scaled physical model, as well as special conditions of rheological tests in the Haake RS1 rotational rheometer cell, made us detecting a correlation between the spreading macroscopic factors and microscopic factors of the rheological behavior of the nanodisperse systems structure in dynamic conditions.
103 to 10–4 s–1 or lower), in nanodisperse systems based on highly dispersed aerosil or aerosil–bentonite compositions, with an increase in the shear rate, a non-Newtonian flow is observed. It is accompanied with a continuous growth of the effective viscosity of the dispersions eff, till the yield point P Pk is reached. At P Pk, the effective viscosity decreases abruptly; the structure decomposes via an aggregate mechanism. Earlier it was believed, that each viscosity level there corresponds to a combination of the full destruction of structural bonds and their partial restoring up to the equilibrium level determined by eff. In addition, the structured dispersed system flow remains Newtonian unless the static yield point has been overcome; it corresponds to the largest viscosity of a virtually undestructed system. Using a special procedure, SEM-imaging of the structure of the bentonite-suspension, as well as the bentonite added with minor amounts of aerosil, was carried out in waterethanol medium. Photomicrographs of structure of the studied nanodisperse systems subject to shearing were obtained. The active filler (aerosil) particles distribution in the model system structure is studied. A procedure of studying the thixotropic properties of the structured nanodisperse systems in dynamic conditions is developed. The complex modeling of the structured nanodisperse system spreading over the scaled physical model, as well as special conditions of rheological tests in the Haake RS1 rotational rheometer cell, made us detecting a correlation between the spreading macroscopic factors and microscopic factors of the rheological behavior of the nanodisperse systems structure in dynamic conditions.
PACS numbers: 47.57.qk; 81.07.-b
DOI: 10.1134/S0033173208050081