PART 2 - CROSSOVER FROM DEPLETION ATTRACTION TO ADSORPTION - POLYETHYLENE-GLYCOL INDUCED ELECTROSTATIC REPULSION BETWEEN LIPID BILAYERS

Using the surface forces apparatus, we have measured the static and hy drodynamic forces between two substrate-supported lipid bilayers in wa ter and semidilute, aqueous solutions of poly(ethylene glycol) (PEG), a neutral polymer for which water is a good solvent. In part 1 (previo us paper in this issue), we presented detailed measurements of depleti on attraction in the presence of 8000 molecular weight PEG. In part 2 (this work), we address the behavior of higher molecular weight 20 000 PEG. Specifically, the higher molecular weight PEG adsorbs to the sur faces and both a steric as well as an unexpected electrostatic repulsi on were measured. We determined that higher MW PEG chelates metal cati ons and thereby induces an apparent electrostatic charge on the bilaye r surfaces upon adsorption.