Effect of temperature on the surface tension of diluted aqueous solutions of 1,2-hexanediol, 1,5-hexanediol, 1,6-hexanediol and 2,5-hexanediol

Surface tension of aqueous solutions of 1,2-hexanediol (1,2HD), 1,5-hexanediol (1,5HD), 1,6-hexanediol (1,6HD), and 2,5-hexanediol (2,5HD) was measured as a function of composition using the method of capillary rise at 283.15, 288.15, 293.15, 298.15, 303.15 and 308.15 K with emphasis in the very dilute region. The experimental data were used according to the model proposed by Connors for liquid solutes. Binding constants were determined for 1,2-hexanediol (1,2HD), 1,5-hexanediol (1,5HD) and 2,5-hexanediol (2,5HD). Infinite dilution activity coefficients were evaluated using the procedure suggested by Gracia-Fadrique and the results are discussed in terms of temperature and the size of the alkyl chain exposed to the solvent. Pure 1,6-hexanediol (1,6HD) is a solid at the selected temperatures so the models mentioned before were not used with this solute. The surface tension data, the binding constants and the infinite dilution activity coefficients were correlated with the position of hydroxyl groups in the solute and the results were used to evaluate the effect of hexanediols on the water structure. (c) 2007 Elsevier B.V. All rights reserved.