Effect of perfluorotetradecanoic acid on the morphology of a photopolymerizable phospholipid monolayer at the air-water interface

Fundamental physical chemical properties of a monolayer film comprised of the chiral, photopolymerizable phospholipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (Diyne PC) and the impact of a model perfluorocarbon, perfluorotetradecanoic acid (PF), on these film properties have been investigated, both with and without UV photopolymerization. Enantiomerically pure Diyne PC formed compact, stable monolayers at the air-water interface, exhibited typical phospholipid phase transitions in surface pressure-area isotherms and yielded micron-scale, linear domains upon film compression. Photopolymerized films were significantly more expanded in comparison with the unpolymerized films and the resulting domains had a spiral morphology with a strongly preferred spiral direction. Mixing Diyne PC with PF altered the isotherm behavior, with the principal effects being a significant reduction in the plateau region associated with the characteristic LE-LC phase transition and no larger-scale spiral domain formation in the monolayers of the mixed films. Results are discussed in the context of interactions between the two different film components and the tendency of perfluorinated surfactants to disperse condensed phase regions of phospholipid-based monolayer films. Overall, the tendency of PF to disperse condensed regions of the film makes patterning of films in mixed phospholipid-perfluorocarbon monolayers particularly difficult.