Polymer adsorption on inorganic particles and rheological properties of the dispersions

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In this study, rheological properties of silica particles dispersed in aqueous solutions of hydroxypropyl methyl cellulose (HPMC) were investigated in combination of adsorption behavior of HPMC on the silica surfaces.1.For the suspensions of fumed silica particles dispersed in HPMC solution, rheopexy and overshooting were observed in transient shear stress, showing the existence of aggregated structure in the dispersions.Evidence of the aggregated structures in the silica suspensions was supported by observations of a bomb at low shear rate in plots of the steady-state shear stress against shear rate (flow curves) as well as a second plateau in the frequency dependence of storage modulus. Moreover, partial desorption of HPMC from the silica particles did not reduce the bomb and the second plateau.2.For the suspensions of colloidal silicas dispersed in HPMC solution, transient shear stress showed no time dependence. The flow curves only indicated shear thinning. The loss modulus was larger than the storage one in the entire range of frequency except for higher frequency, showing liquid-like viscoelastic behavior. The difference in the rheological behavior of the silica suspensions stemmed from the stability of the silica particles : the fumed silicas were aggregated due to their gelling character inwater, whereas the colloidal silicas were electrostatically stable.