A mathematical model for the interactions between non-identical rough spheres, liquid bridge and liquid vapor

► Filling angles for a liquid volume between two spheres depend on the size ratio and surface roughness of the spheres. ► Liquid volume and capillary force relate to the suction, contact and filling angles, spheres roughness, and size ratio. ► The calculated equilibrium relations are shown to possess non-uniqueness. ► For any given humidity of the pore air, the suction increases with increasing particle size and increasing size ratio.