Semifluorinated Alkanes as stabilizing agents of fluorocarbon emulsions

We obtained highly stable, small-sized, and narrowly dispersed perfluorooctyl bromide (PFOB) emulsions using combinations of phospholipids and semifluorinated alkanes CnF2n+1CmH2m+1 (FnHm diblocks) as the emulsifying system. For example, after 6 months at 25 C the average droplet diameter of an emulsion stabilized by F6H10 was only similar to80 nm, compared to similar to180 nm for the reference emulsion stabilized by phospholipids alone. In parallel, a co-surfactant effect has been demonstrated for F8H16 at the water-PFOB interface using pendant drop interfacial activity measurements, which supports the hypothesis that a fraction of the diblocks is located at the phospholipid interfacial film. We also established that the length of the hydrocarbon segment, Hm, must be comparable to that of the phospholipid's fatty chains to obtain the stabilization effect; a strong mismatch leads to rapid coalescence of droplets in the emulsion. For fluorocarbon emulsions, small droplet sizes translate into prolonged intravascular persistence and reduced side effects. FnHm diblocks thus provide a useful, versatile tool to improve the characteristics and stability of injectable fluorocarbon emulsions.