Influence of Na+, Ca2+ on the thickness and free energy of dmpc foam films

Foam films prepared from dispersions of dimyristoylphophatidylcholine (DMPC ) in water and a water-ethanol mixture have been investigated. The thicknes s of the films and their contact angle with the surrounding meniscus of liq uid have been measured as a function on the concentration of NaCl and CaCl2 . The measurements show that the preparation of the lipid dispersions influ ences long and short-range interactions, The binding of Ca2+-ions onto the DMPC headgroups leads to charging of the monolayers and electrical double-l ayer repulsion in the him. There is also some indication for a weak binding of Na+-ions. The free energy of film formation determined from contact ang le measurements provides additional information oil the estimation of the d ifferent contributions to the interaction in the film. (C) 1998 Elsevier Sc ience B.V. All rights reserved.