Small-angle neutron scattering study of aqueous solutions of pentanediol and hexanediol

Aqueous solutions of 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol and 1,6hexanediol have been studied by small-angle neutron scattering over a wide range of concentrations and temperatures. The structure of the solutions on the mesoscopic length scale, corresponding to the intermolecular distances, was analysed with the help of the Kirkwood–Buff formalism. 1,2-Hexanediol solutions exhibited a strong attractive diol–diol interaction, a weak diol–diol attraction was found for 1,6-hexanediol and 1,2-pentanediol, and an extremely weak diol–diol attraction was found in 1,5-pentanediol solutions. The general tendencies are the following: aggregation is stronger as the length of the hydrophobic hydrocarbon chain increases and the 1,2-diols exhibit much stronger attraction then the 1,!-diols. The temperature dependence of the aggregation is weak for the 1,2-diols but strong for the 1,!-diols, indicating in the latter case the hydrophobic character of the interaction.