Abstract
Apparent molar volumes Vφ, apparent molar heat capacities Cp, φ, and relative apparent molar enthalpies Lφ of the mixed solute {di-2-ethylhexyl sodium sulfosuccinate (Aerosol OT, or AOT)+r·H2O} in cyclohexane were determined over the molality range of 0.0002 to 1mol kg-1 at 298.15K. The heats of dilution were measured by using a newly constructed flow-calorimeter. The excess enthalpies for the systems (benzene+cyclohexane) and (chlorobenzene+toluene) at 298.15K were also measured to test the operating technique for the calorimeter. In the system without adding water (r=0) the enthalpy of dilution changes from endotherm to exotherm at about 0.2mol kg-1, and the change in Cp, φ with molality is monotonous. In the systems with r≥5 a sharp peak appears at m=0.001mol kg-1 in Cp, φ and the enthalpy of dilution increases very sharply at m < 0.01mol kg-1. We concluded that the intermolecular interaction of AOT in cyclohexane is moderate, and no micelles are formed. In the systems with r≥5 a transition occurs at m=0.001mol kg-1 and W/O microemultion is formed.
