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

Abstract

The air-water interfacial behavior of Tetronic 90R4 and Tetronic 701 was studied in the presence of sodium salts with different anions namely ${\mathrm{PO}}_4^{3-}$, ${\mathrm{SO}}_4^{2-}$, ${\mathrm{MoO}}_4^{2-}$, ${\mathrm{WO}}_4^{2-}$, Cl^-, Br^-, ${\mathrm{NO}}_3^{-}$, 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 ${\mathrm{PO}}_4^{3-}$< ${\mathrm{SO}}_4^{2-}$< ${\mathrm{MoO}}_4^{2-}$< ${\mathrm{WO}}_4^{2-}$< Cl^-< Br^-< ${\mathrm{NO}}_3^{-}$< 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.