The challenge of breaking open rigid bilayer vesicles upon contact with silica particles was circumvemted by using a dioctadecyldimethylammonium bromide (DODAB) dispersion consisting of open, nanosized bilayer fragments instead of vesicles. At low ionic strength and pH 6.5, DODAB adsorption from bilayer fragments on silica was quantified from adsorption isotherms at 0, 0.1, 0.5, 1.0, and 10.0 mM KCl. Adsorption increased as a function of KCl concentration and surface charge density on particles. The isotherm shapes were typical of competitive adsorption with a maximum possibly due to hydrophobic attraction between adsorbed and free bilayer fragments. Upon adsorption as flat patches on particles, the fragments did not apparently seal into a continuous and closed bilayer surrounding the particle, instead interacted via hydrophobic edges with free fragments in dispersion. At pH 6.5, over a range of DODAB (0-1.0 mM) and KCl concentrations (0.1 - 10.0 mM), from particle sizing, xi-potential analysis, photographs of the mixtures, and particle sedimentation kinetics, the colloid stability of the particles in the mixtures was governed by the ratio R of the total surface areas for bilayers A(b) and particles A(p), R = A(b)/A(p). At R similar to 0.5, the mean xi-potential was zero, the mean particle diameter (Dz) was at maximum, sedimentation was rapid, and colloid stability was at minimum; at R > 1, was positive, Dz was minimized, sedimentation was absent, and colloid stability was high. At low ionic strength ([KCl] < 10 mM), high colloid stability for particles in the presence of cationic bilayer fragments was achieved at or above R = 1, i.e., from the equivalence of total surface areas for bilayer fragments and particles.