Spreading of lipid monolayers on hydrophilic substrates at increased relative humidities

A self-repairing ability of phospholipid monolayers deposited onto thin hydrogel films was observed by fluorescence microscopy, in terms of the expansion and lateral spreading of the monolayer into film defects. The spreading was quantitatively analyzed by covering half of a substrate supporting a thin hydrogel film with a lipid monolayer by Langmuir-Blodgett transfer and observing the spreading of the initially confined monolayer at increased relative humidities due to the hydration of both lipid headgroups and the polymer support. During the observation time of a typical spreading experiment, a constant spreading velocity was observed. A strong influence of monolayer pressure on the spreading velocity was observed. A nonlinear relationship between spreading velocity and monolayer pressure was found, which can possibly be explained by a dependence of the disjoining pressure in the monolayer/substrate interface on the monolayer pressure. The spreading velocity was additionally influenced by the kind of support and by the nature (e.g., phase state) of the deposited monolayer.