Permeation of water vapor through lipid monolayers

Abstract

It is well known that compression of certain insoluble monolayers on an aqueous subphase will reduce the evaporation rate of water (1-3). Permeation of other gases such as 02 and CO2 through lipid layers has also been studied (4, 5). O'Grady (6) measured evaporation coefficients for a clean water surface and surfaces covered with various surfactants, and showed that evaporation coefficients can indeed be reduced by several orders of magnitude. Fat ty alcohol monolayers have been used to reduce evaporation losses on large bodies of water, although this effect has been attributed by MacRitchie (7) to changes in gas phase convective mass transfer at the interface due to the surfactant. Regardless of the mechanism, monolayers of surfactants such as fat ty alcohols at high surface pressure (8, 9) will reduce the evaporation rate of water when compressed. Measurement of evaporation rate has recently been used by Kafka and Pak (10) to model the effect of insulin and other polypeptide hormones on calcium-containing lipid films. The alveolar lining layer of the lung is believed to consist of an aqueous subphase covered by a surface film which is principally dipalmitoyl lecithin (DPL) (11, 12). Pure lecithin monolayers are quite stable and can