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A theoretical spinodal curve for the system water + chloroform + acetic acid at 25 °C is derived using a lattice model for ternary amphiphilic solutions: rod-like molecules covering the bonds of the honeycomb lattice with three-body interactions between the molecular ends associated to the same lattice site. The molecular model is equivalent to the standard Ising model on the same lattice; its mean-field solution is the most appropriate for reproducing, by local fitting, the experimental data for the binodal composition. The derived spinodal curve is in very good agreement with the spinodal composition determined also in the present work from the measured diffusion coefficients recently reported for the same system.

The diffusion coefficients, D ij , for the ternary system water + chloroform + acetic acid are reported at five compositions. This system presents a large solubility gap due to the almost complete insolubility between water and chloroform. The analyzed compositions have a fixed mole ratio of water and chloroform and a decreasing amount of acetic acid when approaching the binodal curve. The difficulty of interpreting the D ij is stressed, and the use of different choices of which component is the solvent and a different reference frame for the diffusive transport is suggested to extract all the possible information from the diffusion coefficients.

Measurements of osmotic coefficients, mutual diffusion coefficients, and conductivity were performed on the binary system sodium n-octyl sulfonate (C8SO3Na)-water at 25degreesC both below and above the micellar composition range. The osmotic coefficient data were obtained through vapor-pressure osmometry, while the Taylor dispersion method was used to measure diffusion coefficients. The mass equilibrium model was applied to this self-aggregating system, taking into account the deviation of the activity coefficients from the Debye-Huckel limiting law by using the Guggenheim corrective terms for mixed electrolyte solutions. The expressions derived from the model fit the experimental osmotic and diffusion coefficient data well, when the same values of aggregation number, fraction of condensed counterions, and equilibrium constant are used. Osmotic coefficients were also used to determine the thermodynamic factor required to compute the solute mobility from diffusion data. Conductivity data were used to test two theoretical models, namely, the Onsager-Fuoss and the Mean Spherical Approximation theories. Both models have been found to yield unsatisfactory fits to our experimental data and some arbitrary terms had to be applied to the theoretical expressions to obtain good agreement between experiment and theory.

Diffusion was systematically studied in the ternary system NaCl (0.5M)−KCl (0.5M)−H2O at 25°C. There were four purposes. First, current methods to extractD ij from Gouy and Rayleigh interferometry data depend on treating theD ij as effectively constant. If concentration differences ΔC i across the boundary are large, this may not be true. To explore this issue, four sets of experiments were performed. Each set had four experiments with approximately the same total number of fringesJ. Each set also had the same corresponding ΔC 1/ΔC 2 ratios as the other three, but the ΔC i were adjusted such that the four sets hadJ≈30, 60, 90, and 120, respectively. Noclear dependence of theD ij on ΔC i was found within their realistic errors. Second, the Gosting diffusiometer can yield both Rayleigh and Gouy fringe patterns during the same experiment. Therefore, theD ij from both methods were compared, and agree well. Third, a new method for analyzing Gouy fringe positions (Miller; program TNY) can be compared to the classical one (Fujita-Gosting; program RFG). TheD ij from both analyses agree well. Fourth, we compared results from the Gosting diffusiometer with those at the same composition from other diffusiometers: one data set by O[Donnell and Gosting from an older Gouy apparatus, and three Rayleigh sets at differentJ values from our older Model H diffusiometer. Results from older diffusiometers were more scattered, but correspondingD ij agree within realistic errors. As reported previously, realistic errors are approximately four times the statistical errors obtained by least squares. Recommended Rayleigh and GouyD ij are presented for this composition.

The four diffusion coefficients describing the isothermal interdiffusion transport in the three-component system BaCl2(1)-KCl(2)-H2O(3) at one concentration were measured. The conditions for the growth of convection inside the diffusion boundary (double diffusive convection) were computed according to the theory proposed by McDougall and compared with the experimental results. Good agreement was found between theory and experimental results. In this system, convection at the borders of the boundary grows even if the heavier components BaCl2 and KCl are more concentrated at the bottom of the diffusion boundary.

A rapid new procedure is described for getting the total number of fringes J from Gouy fringe pattern data. This PQ method is exact and the results excellent (within 0.01–0.03 fringe) for ideal systems (Ωj=0 for all j, Q0=0). Such systems include most binaries; for these, the diffusion coefficient is either constant or a polynomial function of concentration with small concentration differences. For multicomponent systems and some binaries, Q0 can be significantly different from 0. In these cases, the PQ method unambiguously gives the integer number of fringes. If in addition Q0/Q1 is larger than 2.0, then J obtained from a second extrapolation procedure is also good.

Diffusion, density, and viscosity data are collected for the systems α-cyclodextrin and β-cyclodextrin in water. Frictional coefficients were computed with the help of literature activity data and a qualitative discussion of their concentration dependence was attempted.