Kinsi Motomura

Thermodynamic consideration of the mixed micelle of surfactants

In conformity with the conclusion obtained previously, the mixed micelle formation of surfactants was treated thermodynamically as the appearance of a macroscopic bulk phase with the aid of the excess thermodynamic quantities similar to those used for the adsorbed film. The composition of surfactant in the mixed micelle and the thermodynamic quantities of micelle formation were found to be evaluated by applying the thermodynamic equations derived. These equations were extended so as to be applicable to any kind of surfactant mixture. It was shown that the critical micelle concentration vs. composition of surfactant curves form a diagram analogous to the phase diagram of binary mixture. Applying the equation to the published data on typical surfactant systems, this thermodynamic approach was proved to be useful to clarify the miscibility of surfactants in the micellar state.

Thermodynamic studies on adsorption at interfaces. I. General formulation

Abstract In conformity with the view that the evaluation of the thermodynamic quantity of adsorption at a plane interface is essential in understanding the structure and property of interface, a thermodynamic treatment has been developed on the basis of the interfacial excess quantity defined by Hansen [J. Phys. Chem. 66, 410 (1962)] and of the quasithermodynamics. It has been clarified that the partial derivatives of interfacial tension with respect to independent intensive variables determine the interfacial densities of surface-active substances and the changes of entropy and volume associated with the adsorption. By use of these results, the corresponding changes of other thermodynamic quantities have all been evaluated. Further, we have introduced the mean partial molar thermodynamic quantity in the interface and discussed the procedure to estimate the partial molar quantity of the adsorption. The equations have been applied, as an example, to the system consisting of an ideal phase and to the system of two immiscible phases.

Thermodynamic studies on adsorption at interfaces: IV. Dodecylammonium chloride at water/air interface

Abstract The thermodynamic treatment of the adsorption at water oil interface developed in the previous papers has been extended so as to be applied to the adsorption at water/air interface. The surface tension of the aqueous solution of dodecylammonium chloride (DAC) has been measured as a function of temperature and concentration. By applying the thermodynamic relations, the entropy of surface formation Δs and the surface density of DAC Γ 1 H have been calculated. Further, we have shown that the energy of surface formation Δ u can be evaluated numerically. It has been observed that the values of Δs and Δ u decrease, while the value of Γ 1 H increases, with increasing concentration of DAC. It has been found that the adsorbed film transforms from a gaseous to an expanded state at a relatively low concentration, which has been proved thermodynamically. Such a behavior seems to be similar to that at water hexane interface except for the phase transition. The mutual interaction between DAC molecules in the adsorbed film appears to be weakened by the presence of hexane.

The critical micelle concentration of sodium dodecyl sulfate-bivalent metal dodecyl sulfate mixtures in aqueous solutions

Abstract Critical micelle concentrations (CMC) were determined at 30°C for aqueous sodium dodecyl sulfate (SDS)-bivalent metal dodecyl sulfate [M (DS) 2 ] mixtures over the entire surfactant composition range. Bivalent metals used were Mg 2+ , Mn 2+ , Co 2+ , Ni 2+ , and Cu 2+ . The CMC of surfactant mixtures decreased rapidly with the increase of M (DS) 2 content from the value 8.25 × 10 −3 mole/liter for pure SDS to the value 2.7 × 10 −3 mole/liter at 0.2 in mole fraction of M (DS)2, and then asymptotically to the value 1.20 × 10 −3 mole/liter for pure M (DS) 2 . Variation of the CMC with the composition can be explained in terms of an improved Shinodas equation, in which the charge density at the micelle surface and the effective coefficient of an electrostatic contribution to micellar formation defined as K g were modified. An excellent agreement was obtained between experimental and theoretical curves. The same treatment was also successful for the sodium dodecyl sulfate-potassium dodecyl sulfate mixture.

Thermodynamics of interfacial monolayers

Abstract Since the evaluation of changes in thermodynamic quantities by adsorption and phase transition is essential in the study on the structure and properties of interfacial films, a thermodynamic treatment has been developed on the basis of the interfacial excess quantities defined by Hansen and of the quasithermodynamics. Mean partial molar thermodynamic quantities of constituents at the interface have been introduced in the course of development. It has been shown that the partial supposed that ethyl heptadecanoate has a difficulty in arranging its polar head group so as to produce a regular array of condensed monolayer. The above discussion shows that the thermodynamic approach developed in Chapter II serves as a tool for elucidating the structure and properties of interfacial monolayers.

Thermodynamic studies on adsorption at interfaces. II. One surface-active component system: Tetradecanol at hexane/water interface

Abstract In order to show that the thermodynamic [ J. Colloid Interface Sci. 64 , 348 (1978)] treatment developed in Part I is useful in studying the adsorption of surface-active substances at interfaces, comparison has been made with a system consisting of water and dilute solution of tetradecanol in hexane. As the system is trivariant, we have chosen the temperature, pressure, and mole fraction of tetradecanol in hexane for the thermodynamic independent variables and measured the interfacial tension as their functions. By means of the thermodynamic equations derived in Part I, the interfacial concentration of tetradecanol and thermodynamic quantities of interface formation have been determined from the experimental results. Further, the partial molar thermodynamic quantity changes at the adsorption have been calculated. It has been observed that the thermodynamic quantities of interface formation decrease, while the interfacial concentration increases with increasing the mole fraction of tetradecanol. The results are explicable in terms of negative values of the partial molar quantity changes.

Phase transition in the adsorbed films at water/air interface

Abstract The surface tension at the aqueous solution/air interface has been measured for eight surface active substances at 298.15°K under atmospheric pressure. It has been found that each surface tension versus concentration curve has a distinct break at a relatively low concentration and a relatively high surface tension. This result implies that the two states of adsorbed monolayer coexist in equilibrium at the break point. The surface excess numbers of moles of surface active substances and the surface pressure versus mean area per adsorbed molecule curves confirmed that the phase transformation takes place between the gaseous and the expanded states. It has also been shown that the hydrocarbon chain length, and the ionic nature and size of polar head group of a surface active substance have a great influence on the properties inherent in the phase transition.

Thermodynamic studies on adsorption at interfaces: VII. Adsorption and micelle formation of binary surfactant mixtures

Abstract By extending the thermodynamic method developed in this series, a thermodynamic formulation has been proposed to account for the behavior of the adsorbed films of binary surfactant mixtures at interfaces. Further, this formulation has been extended so as to be applicable to the mixed adsorbed films in equilibrium with mixed micelles. The surface tension of the aqueous solution of a decylammonium bromide (DeAB)-dodecylammonium chloride (DAC) mixture has been measured as a function of the total molality of DeAB and DAC and the mole fraction of DAC in the total surfactant at 298.15 K under atmospheric pressure. The total surface density and the compositions in the adsorbed film and micelle have been evaluated by applying the thermodynamic equations derived to the experimental results. It has been concluded on the basis of the surface tension-composition and critical micelle concentration (CMC)-composition diagrams that DeAB and DAC mix slightly nonideally with each other in both the adsorbed film and the micelle.

Thermodynamic studies on adsorption at interfaces

Abstract The thermodynamic treatment of adsorption developed in Part I has been extended so as to include the case of strong electrolytes. By applying the thermodynamic relations to experimental results obtained for the system consisting of aqueous solution of sodium dodecyl sulfate (SDS) and hexane, the thermodynamic quantities of interface formation and partial molar quantities of the adsorption have been evaluated. Their values have been compared with the corresponding ones of tetradecanol described in Part II. It has been observed that SDS has a negative entropy of interface formation which is smaller than tetradecanol, while it has a larger interfacial concentration. This value is closely related to a larger positive value of the volume of interface formation. The above view has been confirmed by changes in the mean partial molar entropy and volume at adsorption. It has also been found from the energy of interface formation and partial molar energy of the adsorption that the adsorption of SDS from aqueous solution is inferior energetically to that of tetradecanol from hexane solution.

Thermodynamics of multicomponent monolayers. I. General formulation

Abstract In view of the fact that monolayers are composed of air, water, and film-forming substances and exist in equilibrium with the adjacent air and water phases, we have derived the fundamental equations to describe the thermodynamic states of multicomponent monolayers. With the aid of the equations, it is clarified that the phase rule in the monolayer system is given in a simple form, which is consistent with modified Defays equation. With respect to thermodynamic function changes on monolayer mixing, we have obtained expressions different from those of Goodrich; the discrepancy is ascribed to his disregard of air and water in the monolayer phase. Phase transitions in the monolayer system are also taken into consideration. General equations have been presented for the partial derivatives of equilibrium surface pressure with respect to temperature and composition. In order to show how to use the derived equations, we have taken up a one-component monolayer, as an example, and indicated that the expressions describing the phase transitions agree with previously published ones.