Effect of temperature on W-shaped excess molar heat capacities and volumetric properties: Oxaalkane-nonane systems

Excess molar volumes V-m(E) of the mixtures diglyme (2,5,8-trioxanonane; TON), triglyme (2,5,8,11-tetraoxadodecane; TODD), or tetraglyme (2,5,8,11,14-pentaoxapentadecane; POPD; E181) + n-nonane have been obtained from density measurements at 278.15, 288.15, 298.15, and 308.15 K. In addition, a micro DSC II differential scanning calorimeter was used to obtain excess molar heat capacities C-p(E) at constant pressure for the same mixtures except for TON + n-nonane and at the same temperatures except for 279.15 K. These results allowed us to calculate the following mixing quantities in the complete range of concentration: alpha, (partial derivative V-m(E)/partial derivative T)(p), and (partial derivative H-E/partial derivative p)(T) at 298.15 K. The excess molar volumes are positive with large maximum values located in the central concentration range with the exception of POPD + n-nonane ar 278.15 K, which has a central miscibility gap. For these mixtures, C-p(E) has a W-shaped concentration dependence: two minima separated by a maximum.