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5.8 Summarized parameters and surface tension in critical mixtures

in which d is the spacial dimension of the system. Unfortunately, it is not possible to find for all considered systems experimental literature data of σ0, probably, due to experimen- tal problems in the determination of this quantity. Nevertheless, in [151], an expression for an ideal surface tension for a mixture σid AB has been presented as mole fraction weighted quantity:

here A, B denote the components and x the mole fraction (x = xc) at critical composition. Surface tension data for pure liquids of all components of binary mixtures presented in Table (5.10) have been found in the literature [151], where for every component the sur- face tension of four temperatures is listed. Values at temperatures between the tabulated ones could be obtained by linear interpolation with an error of less than ±0.02 mN/m. Taken into account the critical temperature of a mixtures as well as using the Eq.(5.31) the surface tension σid AB has been calculated, Table (5.10). In order to perform qualitative

critical Γ0 ξ0 σA(Tc) σB(Tc) σid AB(Tc,xc) mixture 109s−1 nm mN· m−1 mN· m−1 mN· m−1

± 2 ± 0.02 ± 0.1 ± 0.1 ± 0.1 isobutoxyethanol-water [77] 5.3 0.320 27.69 71.66 70.82 ethanol-dodecane [99] 6.4 0.370 38.62 24.52 34.11 nitrobenzene-isooctane [142] 16 0.300 42.86 20.66 30.09 nitrobenzene-n-hexane [143], [144], [145] 20 0.350 42.28 16.68 27.69 2,6-dimethylpyridine-water [123] 25 0.198 35.44 70.47 68.37 methanol-cyclohexane [70] 27 0.330 20.47 22.20 21.34 benzonitrile-isooctane [146] 39 0.270 21.61 21.82 18.58 methanol-n-heptane [147] 44 0.260 21.30 16.68 18.99 methanol-n-hexane [93] 69 0.350 21.30 18.67 19.98 triethylamine-water [136] 90 0.107 20.89 73.01 69.00 nitroethane-3-methylpentane [86] 125 0.230 31.94 17.45 24.70 nitroethane-cyclohexane [90] 156 0.162 32.34 24.85 28.23 n-pentanol-nitromethane [76] 187 0.145 25.12 37.48 32.72

Table 5.10: Amplitude of the characteristic relaxation rate Γ0, and of the fluctuation correlation length ξ0, surface tension σA(Tc), and σB(Tc) of components A, B and ideal surface tension σid AB(Tc,xc) of the mixture, according to Eq.(5.31).

studies of a correlation between characteristic relaxation rate and the surface tension, both quantities have been plotted against another in Fig.(5.56). Unfortunately, the data points do not represent any analytical behavior. Nevertheless, the plot displays three groups of binary critical systems. Group (I) represents binary mixtures, where the characteristic

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