Abstract: The structural parameters of complex systems of seven kinds of aryl sulfonate(synthesized in the laboratory) alkyl aryl sulfonate(AAS)/n-butanol/n-decane/water microemulsions were obtained by means of a dilution method. We also calculated the standard free energy ΔG0o→i of transfer from the continuous oil phase to the interfacial region, the standard enthalpy ΔH0o→i and the standard entropy ΔS0o→i values. The effects of the average molecular mass and its distribution of AAS on the structural parameters and thermodynamic functions were investigated. The results show that the effective radius of dispersive phase Re, the radius of inner sphere water Rw, their difference di, the average aggerate number of surfactant molecules per drop n, have the tendency of normal distribution＜descending distribution＜uniform distribution＜incremental distribution＜reversed normal distribution. The total number of dispersion phase particles Nd and the total interface area of dispersion phase outer sphere Ad appear to be contrary to the above consequence. The values of -ΔG0o→i exhibit the tendency of normal distribution(5.36 kJ/mol)＜descending distribution(5.49 kJ/mol)＜uniform distribution(5.64 kJ/mol)＜incremental distribution(5.78 kJ/mol)＜reversed normal distribution(6.01 kJ/mol). The values of ΔS0o→i have the tendency of normal distribution(26.88 J/(mol·K))＜descending distribution(27.12 J/(mol·K))＜uniform distribution(27.60 J/(mol·K))＜incremental distribution(28.06 J/(mol·K))＜reversed normal distribution(29.23 J/(mol·K)). With the increase of average molecular mass, the values of Rw, Re, n, di, -ΔG0o→i, ΔH0o→i, ΔS0o→i increase while the values of Nd, Ad decrease. In addition, the values of structural parameters, -ΔG0o→i and ΔS0o→i change linearly with the average molecular mass of the AAS, the latter two are y=0.0586x-17916 and y=0.2203x-61.275, respectively.

Key words: alkyl aryl sulfonates, average molecular mass, molecular mass distribution, microemulsion, structural parameter, thermodynamic functions