Rheological studies of hydrophilic and hydrophobic silica suspensions in the presence of adsorbed poly(N-isopropylacrylamide)

The shear flow behavior of silica suspensions for bye different silicas in aqueous poly(N-isopropylacrylamide) was investigated as a function of the volume fraction of the silica particles. The amount of polymer adsorbed on the silica surface was almost constant, irrespective of the silica surface nature, except for the colloidal silica, on which less polymer was adsorbed. The suspensions of the hydrophilic silicas showed shear thinning and pseudoplastic flow. The suspensions of the hydrophobic silica particles showed Newtonian flow at low silica contents, with viscosities comparable to those of the colloidal silica suspensions in the presence of the polymer and those of the suspensions of hydrophilic silica with the same size. With an increase in the silica content the hydrophobic silica suspensions changed from shear thinning to pseudoplastic flow.