Transient and steady-state rheology of silica suspensions in hydroxypropyl(methyl)cellulose solutions

Abstract

Coaxial cylinder rheological measurements have been performed on Aerosil silica suspensions in aqueous hydroxypropyl(methyl)cellulose (HPMC) solutions as functions of both HPMC and silica concentrations for two HPMC samples. Adsorption isotherms of HPMC at the silica particles were measured for various silica contents. In transient experiments rheopexy was found for 5% silica suspensions and stress overshooting behaviour was observed for 7.5% silica suspensions. In the steady-state experiments, a bump was observed at near the shear rates of 0.1 s^–1 in the plot of the steady-state shear stress for 7.5% silica suspensions against the shear rate. Appearance of the bump was attributed to the aggregation characteristics of the silica and it was not influenced by desorption of HPMC from the silica surfaces. Dynamic experiments showed that when the silica content was low, showing a more open network of the aggregated silica, the viscoelastic property of the silica suspension changed from a solid-like to a liquid-like character with increasing frequency. When the silica content was high, indicating a less open network of the structure, the silica suspensions showed a solid-like viscoelastic character. Desorption of HPMC led to a decrease in the viscoelastic moduli.