Is the counterion responsible for the unusual thermodynamic behaviour of the aqueous solutions of gemini bispyridinium surfactants?

Highlights: [•] Apparent and partial molar enthalpies at 298K of the aqueous solutions of cationic gemini surfactants 1,1′-didodecyl-2,2′-trimethylenebispyridinium dichloride (12-Py(2)-3-(2)Py-12 Cl); 1,1′-didodecyl-2,2′-tetramethylenebispyridinium dichloride (12-Py(2)-4-(2)Py-12 Cl); 1,1′-didodecyl-2,2′-octamethylenebispyridinium dichloride (12-Py(2)-8-(2)Py-12 Cl) and 1,1′-didodecyl-2,2′-dodecamethylenebispyridinium dichloride (12-Py(2)-12-(2)Py-12 Cl) have been measured as a function of concentration in order to verify the role played by the counterion in the unusual trend of the apparent and partial molar enthalpies as a function of the spacer length, already found in the case of methansulfonates. [•] The data obtained support the hypothesis of a conformation change dependent on the spacer length, but independent on the counterion. [Copyright &y& Elsevier]