Comparison of size distributions and zeta-potentials for silica and silica-based cationic bilayers. Size distribution and zeta-potential (ζ) for 0.1 mg/ml silica, dispersion of 1 mM DODAB bilayer fragments and silica/DODAB particles prepared from 0.1 mg/ml silica and 0.05 mM DODAB. The intervening medium was 1 mM NaCl, pH 6.3 (A-C) or 5 mM Tris.HCl, pH 7.4 (D-F). Measurements were performed, after 1 h interaction. In each subfigure, mean zeta-potential and diameter ± SE are quoted.