Transfer of Ordered Phospholipid Films onto Solid Substrates from a Drained Foam Film

Bubbles have been formed from solutions of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in formamide. The bubbles were transferred onto a hydrophobic substrate after drainage time of 0-20 min. Drainage time of 20 min is sufficient to generate fully drained bubbles. The structure of the transferred films was investigated with X-ray photoelectron spectroscopy and metastable induced electron spectroscopy. Films transferred after a drainage time of 5 min or less show random orientation of the molecules in the films. Films transferred after a drainage time of 10 min or longer result in films forming a mixture of two different types of structures. The smaller fraction of the transferred film shows random orientation of the molecules. The larger fraction shows preferred orientation of the POPC molecules. In the fraction with preferred orientation the polar part of the POPC molecules forms to a large degree the outermost layer which is different to surfaces of surfactant solutions and to the surface of foam films formed by surfactant molecules. A surface formed by polar groups has a higher surface energy than a film formed by nonpolar groups. The possible reasons for the orientation of the molecules with the polar group pointing to the surface are discussed.