Volumetric properties of some water + monoalkanolamine systems between 303.15 and 323.15 K

Density (ρ) of aqueous solutions of monomethylethanolamine (MEA), monoethylethanolamine (EEA), dimethylethanolamine (DMEA), dimethylpropan-1-olamine (DMPA-1) and dimethylpropan-2-olamine (DMPA-2) is measured at a 5 K interval between 303.15 and 323.15 K in the range of 0 ≤ x2 ≤ 1, where x2 is the mole fraction of alkanolamines. The ρ of the monoalkanolamines is assumed to be related to respective strength of association. Excess molar volumes (VmE) were negative for all systems in the whole range of composition and at all temperatures with minima occurring at x2 ~ 0.35 to 0.40. The depth of minima varied as, W + DMPA-2 > W + DMEA > W + DMPA-1 > W + EEA > W + MEA. Negative VmE were explained by large size difference as well as hydrophobicity effects. Thermal expansivity (α) followed as, W + DMPA-2 > W + DMEA > W + DMPA-1 > W + EEA > W + MEA, while its excess values were found to form distinct minima. The ρ vs. x2 isotherms have been correlated with polynomials, while VmE and αE were fitted to the Redlich-Kister equation. In addition to intermolecular H-bonding, interstitial accommodation, steric effects etc. 'hydrophobicity' of the alkanolamines is suggested to play the most vital role for the systems under investigation.