Rheological properties of sodium montmorillonite dispersions |
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| Affiliation: | 6. Department of Materials and Textiles, Oriental Institute of Technology, New Taipei City 22061, Taiwan;10. Graduate Institute of Biotechnology and Biomedical Engineering, Central Taiwan University of Science and Technology, Taichung 40601, Taiwan;1. School of Chemical Engineering, University of Campinas, Av. Albert Einstein, 500, 13083-852 Campinas, SP, Brazil;2. Institute of Chemistry, University of Campinas, P.O. Box 6154, 13083-970 Campinas, SP, Brazil;1. SP Chemistry, Materials and Surfaces, Box 857, 50115 Borås, Sweden;2. SP Structural and Solid Mechanics, Box 240 36, 40022 Göteborg, Sweden;3. SP Technical Research Institute of Sweden, Sweden;1. Uludağ University, Faculty of Engineering and Architecture, Textile Engineering Department, Bursa, Turkey;2. International Turkmen-Turkish University, Faculty of Engineering, Textile Engineering Department, Koshi, Ashgabat, Turkmenistan;3. Dumlupinar University, Faculty of Engineering, Mining Engineering Department, Kütahya, Turkey;4. Istanbul Technical University, Faculty of Mines, Mineral Processing Engineering Department, 34469 Maslak, Istanbul, Turkey |
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| Abstract: | The rheological behaviour of dispersions of montmorillonite in water is highly pH- and salt-dependent. This is exemplified for 4% (wt/wt) dispersions of montmorillonite from Wyoming and its homoionic sodium form in water, 0.01 M NaCl and 0.1 M NaCl solutions, at different pH and at temperatures from 20°C to 60°C. Generally, the shear stress (for instance, at shear rates of about 100 s−1) decreases sharply in an acidic medium to a minimum around pH 6 (pH 7.5 for the homoionic sodium form) and then increases again very strongly. Thixotropic and antithixotropic behaviour depend on pH, salt concentration and temperature.The presence of Ca2+ ions (molar ratio Na/Ca about 6.5/1) in the “pristine” montmorillonite affects the type of flow very sensitively. Ca2+ ions convert diffuse ionic layers into quasicrystalline structures with a central layer of gegen ions. Attractive potentials are then created in the contact regions between the particles, even in diluted salt solutions. Formation of band-like structures (as in the “Bändermodell” of A. Weiss) is promoted.Further, results are reported on the influence of particle size (fractions < 0.06 μm to 2 μm) on the flow behaviour at different concentrations of homoionic sodium montmorillonites from Amory and Cameron. |
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