Reversible stepwise formation of mono- and bilayers of a fluorocarbon/hydrocarbon diblock on top of a phospholipid Langmuir monolayer. A case of vertical phase separation

Compression of mixed Langmuir monolayers made from combinations of dipalmit oyl phosphatidylethanolamine (DPPE) and the semi-fluorinated alkane C8F17C1 6H33 (F8H16) results in expulsion of the diblock molecule at high pressure. Depending on the DPPE/F8H16 molar ratio, either a monolayer or a bilayer o f F8H16 is formed on top of a DPPE-only monolayer. The structure of the hyd rocarbon and fluorocarbon layers that constitute the resulting vertically s eparated bi- or trilayer was determined using grazing incidence X-ray diffr action. The phenomenon is reversible and represents a novel case of vertica l, pressure-induced phase separation.