Micellar and lyotropic behavior of three isomeric bola‐amphiphiles with pyridinium groups

Abstract

222 R. Festag et al. / Micellar and lyotropic behavior of three isomeric bola-amphiphiles with pyridinium groupsRed. Trav. Chim. Pays-Bas 113,222-230 (1994 Abstract. The micellar and lyotropic phase behavior of three isomeric bola-amphiphiles 1, 2 and 3 based on para-, meta-and ortho-phenylene derivatives with hydrophilic pyridinium headgroups was investigated. The micellar behavior was characterized by surface-tension and conductivity measurements: while the para-substituted amphiphile 1 and the ortho isomer 3 aggregated to micelles, the meta-substituted amphiphile 2 exhibited stepwise, but discontinous self-association. This is explained by the mass-action and phase-separation model. The existence of "premicellar" aggregates and the discontinous aggregation of 2 is evidenced in addition by a difference-spectrophotometroc measurement. The low surface activity and the calculated areas per molecule of 100-200 A2 at the air-water interface agree with a loop-like conformation of all three bolaamphiphiles 1-3. Lyotropic mesophases were found in the high-concentration regime only for the para isomer 1, while 2 formed crystalline-isotropic phases and 3 isotropic phases only. The mesophase of 1 was characterized by X-ray measurements as lamellar.The addition of 1-hexanol as a co-surfactant led to the induction of a lyotropic mesophase for 2. The role of the cosurfactant consists of filling the wedge between the two hydrophobic chains, thus stabilizing the aggregates.

Bolaform Superamphiphile Based on a Dynamic Covalent Bond and Its Self-Assembly in Water

“…Bolaform amphiphiles refer to amphiphiles containing two hydrophilic groups linked by a hydrophobic skeleton. − The solubility and the critical micelle concentration (cmc) of bolaform amphiphiles are relatively lower than those of conventional amphiphiles with the same hydrocarbon/headgroup ratio. Various types of aggregates, such as micelles, vesicles, nanofibers, and nanosheets, can be conveniently constructed by self-assembly of bolaform amphiphiles.…”