Thermodynamic studies on adsorption at interfaces

Thermodynamic Quantities of Surface Formation of Aqueous Electrolyte Solutions

The surface tensions of aqueous salt solutions of LiCl, KCl, and CsCl were measured as a function of concentration and temperature. By analyzing the results, the thermodynamic quantities of surface formation such as entropy (Deltas), Helmholtz free energy (Deltaf), and energy of surface formation (Deltau) were evaluated. Addition of salts into aqueous solution leads to an increase in Deltaf but decreases in Deltas and Deltau. The variations of Deltas, Deltaf, and Deltau with the change of salt concentration are almost the same for all alkali metal chlorides in spite of their large difference in hydration force. Copyright 1999 Academic Press.

Thermodynamic Quantities of Surface Formation of Aqueous Electrolyte Solutions

The surface tensions of aqueous solutions of sodium, magnesium, and lanthanum chlorides were measured as a function of concentration and temperature. By analyzing the results, the concentration dependence of the thermodynamic quantities of surface formation such as entropy (Deltas), Helmholtz free energy (Deltaf), and energy of surface formation (Deltau) were evaluated. The Deltaf increased almost linearly with increasing concentration, and the degree of the increase is mainly determined by the net charges of the salts. The Deltas decreased with the addition of salt into the solution. It was found that the net charge of salts determines the degree of the decrease in Deltas. On the other hand, a slight change in the Deltau is observed because of the opposite contribution of Deltaf and TDeltas to the Deltau value. Copyright 1999 Academic Press.

Thermodynamic Quantities of Surface Formation of Aqueous Electrolyte Solutions

The surface tensions of binary salt mixtures made up from NaCl and MgCl2 in aqueous solution were measured as a function of concentration and temperature. By analyzing the results, the thermodynamic quantities of surface formation such as entropy (Deltas), Helmholtz free energy (Deltaf), and energy of surface formation (Deltau) were evaluated. The Deltaf of the mixtures positively deviates from the straight line connecting those of NaCl and MgCl2 aqueous solutions. On the other hand, Deltas shows negative deviation from the linear relation. Copyright 1999 Academic Press.

Extremely Strong Interaction of Sodium Decyl Sulfate and Decyltrimethylammonium Bromide in Molecular Aggregates

The thermodynamic behavior of a mixture of sodium decyl sulfate (SDeS) and decyltrimethylammonium bromide (DeTAB) in aqueous solution and in molecular aggregates such as surface adsorbed films and micelles was investigated by measuring the electric conductivity and surface tension of the aqueous solutions. The thermodynamic quantities in solution and those in the molecular aggregates were evaluated from the experimental conductivity and surface tension data. The results for molar conductivity showed that dimerization or ion-pair formation of the SDeS and DeTAB molecules does not occur in aqueous solution and the mixture behaves as uni-univalent strong electrolyte below the critical micelle concentration (CMC). Contrary to the results in the aqueous solution, we found significant nonideal behavior in the phase diagrams of surface adsorption; that is, equimolar mixture of SDeS and DeTAB exists in the adsorbed film at almost all compositions irrespective of the bulk composition in the solution. The same result was also observed in the phase diagram of micelle formation. There was no difference in phase diagrams between surface adsorption and micelle formation at the CMC. The great nonideal mixing of SDeS and DeTAB in the molecular aggregates is undoubtedly attributable to the extreme attractive interaction between oppositely charged polar head groups of surfactants as well as to cohesion between hydrophobic groups. Further, in a low concentration region, it turned out that equimolar composition is preserved in the film during phase transition of the mixed adsorbed film of SDeS and DeTAB from a gaseous state to an expanded state.