Calorimetric studies of aggregate formation of oleyl alcohol in oil solutions

The enthalpies of mixing of oleyl alcohol and oils (cyclohexane, benzene) were measured as a function of the concentration at fixed temperatures by the use of a high-accuracy isothermal calorimeter. By applying the thermodynamic equations to the enthalpy of mixing, the differential enthalpies of solution of oleyl alcohol in the oil solution were evaluated. The enthalpies are positive and decrease with increasing concentration in both oils, indicating that the aggregate formation is exothermic. However, the enthalpy of aggregate formation in the cyclohexane solution is much larger than that in the benzene solution and has a magnitude corresponding to the hydrogen bond formation, which was supported by the infrared spectra. Furthermore, the infrared spectra of the benzene solution showed that the hydroxyl group of alcohol attractively interacts with benzene molecule. These experimental results suggested that oleyl alcohol molecules associate themselves through the hydrogen bond formation between the hydroxyl groups in the cyclohexane solution, whereas with keeping finteraction between hydroxyl group and benzene molecule in the benzene solution.