Effect of Hofmeister Anions Series on the Langmuir Film of Tetronic 90R4 and Tetronic 701 Block Copolymers

The air–water interfacial behavior of Tetronic 90R4 and Tetronic 701 was studied in the presence of sodium salts with different anions namely PO43−, SO42−, MoO42−, WO42−, Cl^–, Br^–, NO3−, I^–, and SCN^–. Their presence in the subphase altered the arrangement of both tetronic molecules at the air–water interface. The limiting mean molecular area of the Langmuir film for both tetronics was found to be ion specific; it increased following the series PO43−< SO42−< MoO42−< WO42−< Cl^–< Br^–< NO3−< I^–< SCN^–, which was found to be aligned with the Hofmeister series of anions. Furthermore, the study explored the effects of the hydration enthalpy, free energy, viscosity B_JD coefficient, and polarizability of these anions on the interfacial behavior of tetronics. The Langmuir–Blodgett film morphology was also examined in the presence of these salt species using SEM. Morphologies were explained considering kosmotropic and chaotropic nature of these anions.