OFLOXACIN MICROEMULSION

Microemulsions are thermodynamically stable, but are only found under carefully defined conditions. One way to characterize these systems is by whether the domains are in droplets or continuous. Characterizing the systems in this way results in three types of microemulsions: oil-in-water (o/w), water-in-oil (w/o), and bicontinuous. Generally, one would assume that whichever phase was a larger volume would be the continuous phase, but this is not always the case. Surfactants are molecules that typically contain a polar head group and an polar tail. They are surface-active and microstructure forming molecules with a strong chemical dipole. They can be ionic (cationic or anionic), nonionic, or zwitter ionic. Surfactant molecules self-associate due to various inter and intra molecular forces as well as entropy considerations. All of these serve to optimize the free-energy overall. For example, when surfactant is mixed with oil and water, they accumulate at the oil/water interface, because it is thermodynamically favorable. The surfactant molecules can arrange themselves in a variety of shapes. They can form spherical micelles, rod-shaped micelles, a hexagonal phase (consisting of rod-shaped micelles), lamellar (sheet) phases, reverse micelles, or hexagonal reverse micelles.