The first stages of lipid layer formation. A metastable impact electron spectroscopy study of egg lecithin dissolved in hydroxypropionitrile

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Abstract
By means of metastable impact electron spectroscopy we have studied the surface of a solution of egg lecithin in hydroxypropionitrile (HPN). The concentration has been varied between ∼5 × 10-4 moll-1 and ∼5 × 10-3 moll-1 which is far above the estimated critical micelle concentration. The age of the investigated surface has been adjusted between 2 ms and 18 ms. Within this range of parameters we have achieved full coverage of the surface by lecithin molecules. This situation is characterized by lecithin molecules lying flat on the HPN surface with an occupied area of σLec ⩾ 190 Å2. This value is much larger than found for condensed layers with the hydrophobic tails pointing away from the surface. Thus, we conceive our experiment as the observation of the first steps of spontaneous lipid layer formation.