Evaluating the effects of electrolytes on the interaction forces between alumina surfaces in polyacrylic acid solutions using atomic force microscopy

Evaluation and control of ceramic slurry at the microscopic level are critical to ensure consistent quality in manufactured ceramics. Notably, metal ions such as Mg²⁺ and Al³⁺ are common in ceramic slurries and significantly influence the stability of particle. This study applied atomic force microscopy to investigate the interaction forces between alumina particle surfaces in the presence of different concentrations of three metal ions and polyacrylic acid (PAA), a widely used dispersant.

The attractive forces observed at low PAA concentrations were attributed to polymer bridging between alumina surfaces, whereas the repulsive forces observed at high PAA concentrations were attributed to the domination of steric repulsion between adsorbed PAA molecules. The presence of multivalent metal ions, such as Mg²⁺ and Al³⁺, modulated these interactions; an increasing ion valence induced a transition from repulsive to attractive force, primarily owing to electrostatic screening, which caused conformational collapse of the PAA chains and diminished the range of steric repulsion. Similarly, increasing the concentration of these metal ions decreased the range of repulsive forces, eventually resulting in a net attraction driven by the same electrostatic and polymer conformation mechanisms. Notably, the addition of 0.1 M AlCl₃ produced an anomalous long-range attraction between surfaces that could not be explained by conventional mechanisms, such as polymer bridging or electrostatic interactions between charge domains.