Foulant-foulant and foulant-membrane interfacial interactions play an important role in dictating the extent of fouling. In order to understand the impact of the surface energy of particulate foulants on the fouling extent, the direct observation through the membrane (DOTM) technique was used to characterize critical flux and also assess the initial evolution of foulant deposition. Polystyrene and glass with diameters approximating 10 pm were used as foulants because (i) the similar particle diameter eliminated the differences due to particle back-transport, and (ii) the Gibbs free energies (Delta G) of foulant-membrane and foulant-foulant interactions were both negative (i.e., attractive) for polystyrene and both positive (i.e., repulsive) for glass. Results indicate that: (1) because of the attractive and repulsive foulant-membrane interactions of the polystyrene and glass, respectively, (i) critical flux was lower for polystyrene than glass, (ii) the phenomenon of a flowing particle layer was observed at a lower cross-flow velocity (CFV) for glass than polystyrene, and (iii) relaxation was more effective for glass than polystyrene; (2) because of the attractive and repulsive foulant-foulant interactions of the polystyrene and glass, respectively, clustering was observed for the former but not latter; (3) out of the four particle deposition mechanisms (namely, convective, entrapment, dead zone and clustering) distinguished, the first three occurred for both attractive and repulsive interfacial interactions, but the forth (i.e., clustering) only occurred when foulant-foulant interactions were attractive. (C) 2016 Elsevier B.V. All rights reserved.