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

Excess molar volumesV _m ^f of the mixtures diglyme (2,5,8-trioxanonane: TON), triglyme (2.5,8,11-tetraoxadodecane: TODD), or tetraglyme (2,5,8,11,14-pen-taoxapentadecane: 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 capacitiesC _p ^E at constant pressure for the same mixtures except for TON+n-nonane and at the same temperatures except for 278.15 K. These results allowed us to calculate the following mixing quantities in the complete range of concentration: α(∂V _m ^υ /∂T) _p , and (∂H ^υ/∂p)nT at 298.15K. The excess molar volumes are positive with large maximum values located in the central concentration range with the exception of POPD +n-nonane at 278.15 K, which has a central miscibility gap. For these mixtures,C _p ^F has a W-shaped concentration dependence: two minima separated by a maximum.