The solution states of Aerosol OT (di-ethylhexyl sodium sulfosuccinate) in organic solvents, especially in CCl
4, were investigated with measurements of the distribution of Aerosol OT between aqueous and organic media, the vapor pressure depression of solvent, and the interfacial tension between mercury phase and organic solution phase. With the analysis of data of the first two measurements, Aerosol OT in CCl
4 was concluded to be all in monomeric state (I) below 10
-6 molality and in an equilibrium state (II) consisting of monomer and micelle above 10
-3 molality, respectively. The aggregation number of the micelle was found to be 17, which did not vary with the change of temperature. This constancy of the aggregation number against temperature change can suggest the monodispersion of micelle, according to the thermodynamic argument of Hill. This suggestion was also confirmed by the good agreement between the number average aggregation number of micelle from our vapor pressure measurement and the weight average one from the ultracentrifuge measurement cited in literature. The concentration of transition between site I and state II, i.e., CMC, of Aerosol OT in CCl
4 was estimated to lie in the neighbourhood of 2×10
-4 molality by the result of interfacial tension measurement.
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