Properties of Carbopol Solutions as Models for Yield-Stress Fluids |
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Authors: | S.J. Curran R.E. Hayes A. Afacan M.C. Williams P.A. Tanguy |
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Affiliation: | Authors Curran, Hayes, Afacan, and Williams are with the Dept. of Chemical and Materials Engineering, Univ. of Alberta, Edmonton, Alberta, Canada T6G 2G6. Author Tanguy is with the Dept. of Chemical Engineering, Ecole Polytechnique, Montréal, Québec, Canada H3C3A7. Direct inquiries to author Williams (E-mail: ). |
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Abstract: | ABSTRACT: The effect of pH on the non-Newtonian viscosity (η)of aqueous Carbopol 940 solutions is presented with high resolution (pH increments about 0.4) between pH = 2.8 and 12.7. Aqueous NaOH was used to adjust pH of 1.48 wt % Carbopol solutions. A Contraves viscometer was used to measure steady-flow shear stress at known shear rate (γ) over the range γ= 8 to 195 s−1. Yield stresses and shear-thinning η(γ) were observed. Data were fitted with a Herschel-Bulkley model, whose parameters (including yield stress) were expressed as functions of pH. Comparisons were made of η(γ) to the dynamic viscometric properties η'(ω) and η*(ω) for comparable ranges of γ and frequency (ω): A fairly close match was found between η and η* but η«η'. pH dependence included previously unreported extrema of h(pH) in the range of pH = 6.2 to 6.6. Because of sensitive control of rheological properties with pH, Carbopol solutions can be used to mimic a great range of shear-thinning and yield-stress behavior that should make them useful for model studies directed toward process and equipment design and evaluation. |
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Keywords: | viscosity yield-stress fluids Carbopol solutions pH dependence |
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