The interaction between stearic acid monolayers and butane under elevated pressures

• The interaction between a Langmuir film and butane at increased pressure is studied.
• Gas molecules accumulate between the lipid head groups of the lipids.
• In parallel the long-range lateral crystallographic order of the film is increased.
• At increased pressure, the lipids are dissolved in adsorbed gas molecules.
• Solvent gases have thus a strong impact on the structure of lipid systems.

A study on the interaction between butane and lipid membranes is presented. Monomolecular films of stearic acid were prepared on a water surface and were exposed to dense gas phases of n-butane and isobutane. From X-ray reflectivity measurements and grazing incidence X-ray diffraction, the accumulation of gas molecules at the liquid–gas interface was analyzed. We show that the gas molecules penetrate into the lipid membrane and accumulate between the head group and tail group of the lipids. This process goes in hand with an increase of the long-range lateral crystallographic order within the lipid film. This and the formation of multilayer islands points to an expulsion of lipids by the gas molecules. At higher pressures close to the condensation pressure of the studied gases, the vertical and lateral order is lost, indicating an adsorbed liquid film in which the lipids are dissolved.

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