Thermodynamic activation parameters for viscous flow of dilute aqueous solutions of ethylenediamine, trimethylenediamine and N,N-dimethyltrimethylenediamine.

The density and the viscosity data have been used to determine the thermodynamic activation parameters, free energies (ΔG‡), enthalpies (ΔH‡) and entropies (ΔS‡), for viscous flow of the systems; water (W) + ethylenediamine (ED), W + trimethylenediamine (TMD) and W + N,N-dimethyltrimethylenediamine (DMTMD) in the temperature range of 303.15-323.15 K over the composition range of 0 ≤ X2 ≤ 0.45, where X2 is the mole fraction of diamines. On addition of diamines to water, ΔG‡, ΔH‡ and ΔS‡ values increase sharply, pass through a maximum and then decline. The heights of maximum in the ΔG‡ versus X2 curve vary as, W + DMTMD > W + TMD > W + ED. For all systems, the excess properties, ΔG‡E, ΔH‡E and ΔS‡E are positive. The observed increase in thermodynamic values may be due to combined effect of hydrophobic hydration of diamines and water-diamine interaction as a result of hydrophilic effect. [ABSTRACT FROM AUTHOR]