Aggregation of quaternary ammonium gemini surfactants C12-s-C12⋅2Br in n-heptane/n-hexanol solution: Effect of the spacer chains on the critical reverse micelle concentrations

The critical reverse micelle concentrations of C12-s-C12⋅2Br (s=2,3,4,5,6,8,12)(s=2,3,4,5,6,8,12) in n-heptane/n-hexanol solutions, cmcI s, have been determined by absorption spectrum method using iodine as probe. The values of cmcI s are smaller than those of the critical micelle concentrations (cmcaq s  ) in aqueous solution and reach a maximum at s=4s=4, which is similar to the variation of cmcaq with s. The variation of cmcI with s is attributed to the alteration in the spacer chain conformation, i.e. when the spacer is short enough, it may adopt stretch configuration and when the spacer is long, it tends to bend towards the continuous oil phase to achieve a more densely packing of the quaternary ammonium heads on the surface of the core.

Graphical abstractThe gemini surfactants C12-s-C12⋅2Br (s=2,3,4,5,6,8,12)(s=2,3,4,5,6,8,12) form reverse micelles in n-heptane with the assistance of n-hexanol. The variation of the critical reverse concentration (cmcI) with s is attributed to the change of folded conformation of the spacer chain.Figure optionsDownload full-size imageDownload as PowerPoint slide