Thermodynamic Analysis of the Adsorbed Film of Sodium Taurodeoxycholate Formed at the Aqueous Solution/Hexane Interface

The thermodynamic properties of an adsorbed film of sodium taurodeoxycholate formed at the solution/hexane interface have been investigated by measuring interfacial tension as a function of temperature and concentration. By analyzing the results, we evaluated the thermodynamic quantities of interface formation and the change in apparent molar quantity with adsorption such as entropy, Helmholtz free energy, and energy. Comparing the results with that observed for an adsorbed film formed at the solution/air surface ( J. Colloid Interface Sci., 196, 123 (1997)), we have shown that transfer of sodium taurodeoxycholate from the solution/air interface to the solution/hexane interface is accompanied by negative changes in partial molar quantities of Helmholtz free energy, enthalpy, and energy. Further, we have shown that sodium taurodeoxycholate takes a more restricted conformation at the solution/hexane interface than that at the solution/air interface.