Catanionic surfactant films at the air–water interface

A catanionic surfactant consists of paired oppositely charged surfactant ions, acting as counterions to each other. In this work, a series of catanionic surfactants with the cationic quaternary ammonium group and anionic sulfate group, with variation of chain length and number of chains, have been synthesized. The results of the Langmuir pressure–area isotherms, for compression and cycles of compression–decompression, have been used to discuss the effect of length and number of hydrophobic chains on the phase behavior and molecular organization of the spread catanionic film. The molecular desorption from the catanionic film, involving either dissolution of the catanionic surfactant or desorption of the organic counterion (short chain ionic moiety), is critically discussed.