Thermodynamic Study of Gaseous Adsorbed Films of Sodium Taurocholate at the Air/Water Interface

Abstract

The surface tension of the aqueous solution of sodium taurocholate was measured in the temperature range 15−35 °C at 2.5 °C intervals and concentration range 0−6 mmol kg -1 . Sodium taurocholate was strongly adsorbed and formed a saturated adsorbed film at a dilute concentration. It was found that the gaseous/expanded phase transition does not take place in the film, while it does in those of common ionic surfactants. By means of the thermodynamic equations ( J . colloid Interface Sci . 1978, 64, 348), thermodynamic quantities of interface formation were obtained and partial molar thermodynamic quantities are evaluated at the infinite dilution. It was seen that partial molar quantity changes associated with adsorption does not depend on the interfacial density of the adsorbed taurocholate ions. The results indicated that the lateral interaction between sodium taurocholate molecules are not strong enough for a phase transition in the adsorbed film to take place.