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1 Bulletin of the Polish Academy of Sciences. Chemistry

1 2003

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Electroviscous effects in nanosized colloid silica suspensions

Adamczyk Z., Jachimska B., Kolasińska M., Karwiński A.

Bulletin of the Polish Academy of Sciences. Chemistry

2003

Vol. 51, No. 3-4

155-168

Viscosity of nanosized colloid silica suspensions was determined as a function of their weight fraction reaching 50%. The experiments have been carried out at fixed pH =10 and controlled ionic strength. It was found that for low concentration range, viscosity of silica sols increased more rapidly than the Einstein theory predicts. This deviation was much larger than predicted theoretically by taking into account the primary electroviscous effect. This discrepancy was explained by postulating a highly porous, gel-like structure of colloid silicas used in our experiments. Accordingly, the apparent hydrodynamic radius of silica particles in aqueous suspensions became much larger than the primary particle size in accordance with previous observations. Based on this postulate, the apparent density of the silica sols was found to be 1.32-1.37 g/cm3 instead of 2.2-2.32 g/cm3 as determined from the suspension dilution method. This corresponds to particle porosity in the range of 75 to 86%. It was also observed that for higher concentration range, silica viscosity increased more rapidly with increased sol concentration than predicted by the Batchelor model derived for hard particles with the corrected hydrodynamic radius. The deviation was attributed to the secondary electroviscous effect stemming from the electrostatic interactions among silica particles in sheared suspensions. It was found that this effect can be quantitatively interpreted in terms of the Russel's theory. On the other hand, for the high concentration range the experimental results were accounted for by the Krieger-Dougherty model. In view of that experimental evidence it was suggested that the structure of nanosized particles can be well characterised via the viscosity measurements.