The interaction between dioctadecyldimethylammonium bromide (DODAB), chloride (DODAC), or acetate (DODAAc) cationic bilayer fragments (BF) and polystyrene sulfate (PSS) particles (2 x 10(11) particles/mL) was evaluated at and above equivalence of total surface areas for bilayers and particles (A(b)/A(p)) over a range of low NaCl and lipid concentrations, by means of zeta-potential, zeta, and particle diameter, D-z, analysis. In pure water, lipid addition at and above A(b)/A(p) = 1 rapidly increased D-z and zeta, which reached stable plateau values above those expected at bilayer coverage. By addition of small NaCl concentrations (0.05-5.00 mM), D-z decreased with zeta still positive. Therefore, the effect of low salt concentration on the particle coverage with lipid bilayer fragments was surface rearrangement of bilayer fragments on the surface from uneven coverage with some bilayer fragments adsorbed vertically, to perfect bilayer coverage upon addition of small amounts of NaCl. This occurred over a broad range of lipid concentration (0.04-1.0 mM DODA), possibly due to NaCl-induced sealing of adjacent bilayer patches adsorbed on particles. At 0.2 mM lipid, the effect of salt, counterion, and bilayer type (BF or large vesicles, LV) on surface tension at the air-water interface (gamma) complemented the evaluation of bilayer behavior at a hydrophobic interface. The gamma decay rate and total extent increased with counterion size, NaCl concentration, and frequency of hydrophobic defects in the lipid bilayer. Upon addition of 2 mM NaCl to 0.2 mM DODAB BF or LV, gamma decay was much faster for BF, showing the importance of hydrophobic defects in the bilayer to induce its fusion to the air-water interface.