Excess molar volumes of aqueous systems of some diamines

Densities of the systems, water (W)+ethylenediamine (ED), W+trimethylenediamine (TMD), W+1,2-diaminopropane (DAP), and W+N,N-dimethyltrimethylenediamine (DMTMD), have been measured for the whole range of composition at temperatures ranging from 303.15 to 323.15 K. The densities, ρ, excess molar volumes, VmE, thermal expansivities, α, and their excess values, αE, have been plotted against mole fraction of diamines. The density curves for the systems, W+ED, W+TMD, and W+DAP are quite similar to one another with humps in the water-rich region but dissimilar to those of W+DMTMD. Excess molar volumes are negative and large in magnitude and are marked by well-defined minima in water-rich region. The temperature has little effect on VmE. The large negative VmE, the depth of minima in VmE, and the position of minima for different systems along the composition axis have been discussed mainly in terms of hydrophobic hydration. At higher concentration of diamines, the variation of VmE is attributed to hydrophobic interaction. Thermal expansivities have been found to rise up sharply in water-rich region, followed by a slower rate as the concentration of diamines is continuously increased. The excess expansivities have been found to be positive for the whole rage of composition.