Viscosity of dilute aqueous solutions of some diols

Viscosities of the aqueous solutions of ethane-1,2-diol, propane-1,2-diol, butane-1,2-diol, butane-1,4-diol and butane-2,3-diol up to a composition range of 0.1 mole fraction of diol have been determined at temperatures varying from 303.15 to 323.15 K, with an interval of 5 K. The viscosities and excess viscosities increase progressively with the increase of diol concentration. The free energies, excess free energies, entropies and excess entropies of activation for viscous flow also increase with diol concentration. The magnitude of all these parameters, except entropies and excess entropies, follows the order, butane-2,3-diol + water > butane-1,4-diol + water similar to butane-1,2-diol + water > propane-1,2-diol + water > ethane-1,2-diol + water. The hydrophilic and hydrophobic effects are considered for the interpretation of viscosities and the thermodynamic parameters of all aqueous diols, excepting ethane-1,2-diol + water system, for which the observed properties have been explained mainly in terms of hydrophilic effect.