Polymer Adsorption Effects on Structures and Rheological Properties of Silica Suspensions

Abstract

By a combination of small angle neutron scattering (SANS) and rheological measurements, characterization of silica suspensions in aqueous (hydroxypropyl)methyl cellulose (HPMC) solutions and their shear stresses and dynamic moduli measurements were performed as a function of concentrations of silica, HPMC, and isopropyl alcohol, which plays a role to displace molecules of HPMC. Aerosil and Snowtex C silicas were used : the former is easily to aggregate in water and the latter is stable in water, and the respective structures were confirmed by a SANS technique. From the SANS measurements, adsorption of HPMC induced a small portion of the Snowtex C silica particles to form a cluster, whereas it did not influence the self-similar structures of Aerosil silicas suspensions. The amounts of HPMC adsorbed on the silica surfaces decreased with an increase in the displacer concentration. In the flow curves, plots of steady-state shear stress against the shear rate of the Aerosil silica suspensions, there was a bump, which is more like a plateau around 0.1 s -1 , in shear rate and this bump did not disappear with addition of isopropyl alcohol. However, the shear stress of the Snowtex C increased monotonically with an increase in the shear rate and its magnitude decreased with increasing displacer concentration. Upon addition of isopropyl alcohol the dynamic moduli of the respective silica suspensions decreased with the amounts of HPMC desorbed from the silica surfaces. For the Aerosil silica suspensions the storage modulus was more sensitive to the adsorbed amounts of HPMC than the loss modulus.