Electrosteric stabilisation of colloidal zirconia with low-molecular-weight polyacrylic acid. An atomic force microscopy study

The adsorption of low-molecular-weight polyacrylic acid (M_r = 2000) on zirconia has been studied as a function of pH. In this study, an atomic force microscope (AFM) was used to monitor directly the changes in polymer conformation at the solid/water interface. Force-distance profiles were obtained at AFM scan rates equivalent to those expected for Brownian collision rates. The size of the steric interaction lengths between the surfaces was seen to increase as a function of increasing pH. These increases were related to the increasing size of the adsorbed polyelectrolyte owing to decreasing segment-surface affinity and increasing segment-segment repulsions at higher pH. Data at low pH were used to estimate the size of the uncharged collapsed polymer coil at the interface. Best fits of the long-range electrical double-layer interactions allowed an estimate of the effective plane of charge at each pH for the adsorbed polyelectrolyte.