Effect of salinity on adsorption and interaction forces of hydrophobically modified polyacrylamide on silica and alumina surfaces

Abstract

In this work, the adsorption behaviors and interaction forces of different polymers on silica and alumina surfaces have been investigated under the effect of KCl concentration using quartz crystal micro-balance with dissipation (QCM-D) monitoring technique, viscosity measurement and atomic force microscopy (AFM) colloidal probe technique. Polyacrylamide (PAM) and hydrophobically modified polyacrylamide (HMPAM) with hydrophobic monomer (i.e., hexadecyl dimethyl allyl ammonium chloride (C16DMAAC)) have been investigated as model polymers. It is found that the adsorption amounts of HMPAM and PAM polymers on negatively charged silica and positively charged alumina surfaces increase with increasing solution salinity (1–100 mM KCl). HMPAM displays higher adsorption capacity than PAM on both silica and alumina surfaces, which is attributed to the hydrophobic interaction originated from the long hydrocarbon chains of HMPAM. Furthermore, the measured adhesion between the polymers and the substrate surfaces is found to decrease for the alumina cases and increase for the silica cases with increasing the salinity, which is due to the weakened electrostatic interactions between the polymers and substrate surfaces under high salinity (i.e., 100 mM KCl). The viscosities of PAM and HMPAM solutions are found to decrease with increasing solution salinity, which could be caused by the much more coiled conformation of PAM and HMPAM chains at higher salinity. Both the interactions between the polymer and substrate surface and the polymer conformational changes play important roles in the polymer adsorption behaviors on silica and alumina surfaces.