Interfacial and micellar behaviour of pyrrole-containing surfactants

Abstract

The physicochemical properties of new electropolymerisable cationic surfactants having a pyrrolyl group attached and unusual counterions have been studied in aqueous solutions and at the air-water interface. The tetrafluoroborate and tosylate anions behave as quite hydrophobic counterions as compared to the conventional bromide. The pyrrolyl group of moderate polarity has a dual behaviour it behaves as a hydrophobic substituent when it is attached close to the polar head of the surfactants, but its low polarity manifests when it is attached to the end of the hydrophobic chain. Thus, the presence of the pyrrolyl group at the chain end does not affect the cmc value. The pyrrole ring was found located at the micellar surface in the dilute regime; the resulting folding of the hydrophobic chain induces a strong curvature of the interface; small and spherical micelles are formed. A concentrated regime is reached where the interfacial curvature is reduced: the micelles progressively grow in size and change their shape into elongated ellipsoids. The increasing lateral interactions at the level of the headgroups expel the pyrrolyl groups into the hydrophobic micellar core.