The influence of ionic strength, pH of the solution and molecular weight of polyacrylic acid (PAA) on its adsorption and the electrical double layer (Al2O3/polyelectrolyte solution) properties have been examined. The measurements show that the adsorption increases with increasing ionic strength and molecular weight of the polymer, whereas the increase in pH reduces the adsorption. The thickness of the PAA adsorption layer onto aluminium oxide and the expansion coefficient were also calculated. The increase in ionic strength, pH of the solution and polymer molecular weight causes an increase in adsorption layer thickness and expansion coefficient of PAA. (c) 2005 Elsevier B.V. All rights reserved.