Gemini surfactants with acetylenic spacers

A total of 24 dicationic geminis surfactants were synthesized, having a 2-butynyl spacer and chain lengths varying from 8 to 18 carbons. Geminis with more flexible butyl spacers were also synthesized for comparison purposes. Tensiometry gave critical micelle concentration (cmc) values, surface activity, and Gibbs areas. Film studies on the C-18 geminis gave liftoff and collapse areas. The acetylenic geminis behave normally with the log cmc values decreasing linearly with chain length for all the dibromide salts. Anomalous behavior occurred, however, with the C-18 gemini having a butyl spacer. It was found that cmc data correlate with spacer area, a relationship ascribed to packing constraints on curved surfaces and, possibly, to steric inhibition of ion binding. The effects are accentuated with the C-18 surfactants. Geminis with heterocyclic headgroups were examined.