Phospholipid black foam films: dynamic contact angles and gas permeability of DMPC bilayer films

The behavior of bilayer Newton Black Films (NBF) from aqueous dispersions of dimyristoylphosphatidylcholine (DMPC) have been studied in dynamic conditions. The dynamic contact angles θ and the gas permeability coefficient K have been measured using the diminishing bubble method. Two different solutions have been used: (i) DMPC vesicle suspension in water obtained through sonication and (ii) DMPC dissolved in ethanol plus water mixed solvent. Both solutions contain 0.1 M NaCl. The behavior of the dynamic contact angles is very different for NBF from the two types of solutions. In the case (i) the initially constant θ(t) sharply increase after approximately 2 h of the spontaneous diminishing of the bubble, they follow the gas pressure variation in the cell and depend on the film area. On the contrary in case (ii) the θ(t) values are almost constant during the spontaneous diminishing of the bubble as well as during the gas pressure variation in the cell and they do not depend on the film area. The gas permeability coefficient is larger in case (ii). The results are discussed in connection with the thickness and structure of the NBF from the two types of solutions, taking into account the solubility (or insolubility) and the hydration of the adsorption layers of the DMPC molecules.