Increase in the effective viscosity of nanodisperse structured systems in shear deformation at extremely low rates
| Autor: | Yu. S. Svistunov, A. N. Potapov, N. B. Ur’ev, V. A. Starikov |
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| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | Doklady Physical Chemistry. 416:237-239 |
| ISSN: | 1608-3121 0012-5016 |
| Popis: | In this work, it was detected for the first time that, in the range that was previously deemed to be the range of the Newtonian viscosity η 0 , systems with lyophobic interactions of particles are characterized by a nonlinear dependence of the viscosity on the shear stress with an increase in the shear rates in the range 0 ≤ ≤ 10 –3 s –1 . The viscosity increases until the yield strength P k , after which an avalanche-like breakup of the structure starts. A specific feature of the flow of the considered structured dispersions in the range P < P k is that the viscosity increases in a sawtooth manner, which is typical of breakup of the structure into aggregates of particles with subsequent restoration and strengthening. This phenomenon can be explained by an increase in the probability of contacts between particles and aggregates of particles at lyophobic parts of the surface (if there is a lyophobic‐lyophilic mosaic pattern [5]). In this work, we studied suspensions of modified (methylated) nanodisperse Aerosil in mineral oil with concentrations of 2‐7 wt %. The total flow curves of the studied suspensions under quasi-equilibrium conditions were recorded with a Haake RS1 rotational rheometer in a controlled stress mode where the shear stress was specified discretely and the shear rate was controlled. Reaching of a quasi-equilibrium state at each point was detected by the device automatically once the amplitude of oscillations of a parameter being measured reached 1% of the mean. Great attention was paid to studying the behavior of structured nanodisperse systems in the range of extremely low shear rates e ˙ (on the order of 10 –6 s –1 ). Detailed data were obtained on the structural‐rheological properties of suspensions in the highest viscosity range characterizing the virtually unbroken structure of the system. |
| Databáze: | OpenAIRE |
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