CONICET | Buscador de Institutos y Recursos Humanos

Lipid miniemulsions (ME) are oil in water dispersions stabilized by an interfacial layer of asurfactant are systems commonly used to encapsulate, maintain and release moleculesof pharmacological interest. In this context, Langmuir monomolecular films (LF) at theliquid-liquid interface can be used as experimental models to investigate the dynamicbehavior of surfactants at the oil-water interface in ME.We studied monomolecular layers at the oil/water interface (O/Wint) in a Langmuir interfacial trough using egg-yolk phosphatidylcholine (EPC) (the model phospholipid) andVaseline (VAS) as oil phase. The temporal dynamics in the surface pressure (π) evolutiondepended on the method (spreading/adsorption) used for monolayers preparation andreflected the different distribution of EPC between all the system compartments (bulkphases and interfaces). We distinguished between EPC located either stable at theinterface or hopping between the interface and bulk phases. The size order of theapparent mean molecular area, at constant π, of EPC at different interfaces (EPCO/W >EPC/VAS0.02;A/W > EPC A/W), suggested that VAS molecules intercalated between thehydrocarbon chains of EPCO/W, at a molar fraction xVAS > 0.02. However, EPC/VAS0.02;A/Wshowed the highest compressional free energy. This leaded us to study the EPC/VAS0.02mixture at A/W by Brewster Angle Microscopy (BAM), finding that upon compression VASsegregated over the monolayer, forming non-coalescent lenses (as predicted by thespreading coefficient S = −13 mN/m) that remained after decompression and whoseheight changed (increase/decrease) accompanied by the compression/decompressioncycle. At the O/Wint, while some VAS molecules remained at the interface up to thecollapse, others squeezed out towards the VAS bulk phase with an energy requirementlower than towards the air.