By the addition of isobutylene-maleic anhydride copolymer, Al2O3 aqueous suspensions retain fluidity for approximately 1 h and then gelation occurs. The bi-functionality mechanism as dispersant and gelling-agent of the copolymer was investigated by colloidal probe atomic force microscopy. The time-dependent surface interaction between Al2O3 particles and sapphire substrates were compared to those of SiO2, the suspension of which did not appear experience gelation. After 40 min, repulsive forces increased slightly and attractive forces decreased dramatically with short-range character, corresponding to the dispersant action of the copolymer in aqueous Al2O3. As aging time increased to 2 h. a large repulsive force and long-range attractive force developed. With the aging time going to 3 h, the repulsive force disappeared and only long-range attractive forces remained. On the contrary, in the case of SiO2, long-range repulsive force was only observed after the addition of ISOBAM, and long-range attractive interactions were not observed with increased of aging time. However, no time-dependent long-range attractive interaction was observed in the SiO2 suspension. Therefore, it seems gelation of the Al2O3 aqueous suspension was correlated to the long-range attractive interaction between Al2O3 surfaces. (C) 2019 Elsevier B.V. All rights reserved.