The influence of interfacial properties on the stability of black lipid films

Abstract

By considering the interfaces between the lipid phase (O) present in the border of a black lipid film, the solid (S) supporting the film, and the aqueous phase (W) present on both sides of the film, a stability condition for the film is derived from the Young-Dupré equation. This condition expresses that, in a stable film, the film tension must balance the difference between the tensions of the S/W and the S/O interfaces. It is shown how this difference can be obtained experimentally by measurements of the contact angles and surface tensions present in sessile drops of water and of oil on the solid material. Such measurements have been carried out with mixtures of glycerol mono- and dioleate on different solids (mainly, Teflon and polyethylene). The stability of black films, prepared according to Montal and Müller ( Proc. Nat. Acad. Sci. USA 69, 3561 (1972) from two monolayers, has been examined with the same lipid and solid materials. For these systems it is found that stable bilayers can be formed only with those lipid mixtures that, according to the derived theoretical predictions, should stable films. The poor stability of black phospholipid films prepared by the monolayer technique can be explained qualitatively with the same theory.