Investigation of fine structure in the steps observed in the intermolecular activation energy of viscous flow of ethylene glycol

Abstract

Previous experiments had shown that, whereas the steps in the intermolecular activation energy epsilon of viscous flow of water are sharp and separated by intervals of nearly 6 °C, the steps in ethylene glycol occur at about 12 °C intervals and the drop from one to the next is very gradual (Qurashi and Ahsanullah 1961, Rauf and Qurashi 1959). The measurements on ethylene glycol, using the equation Δ ln η/ΔT = - (/κ)/T2, have now been repeated with more refined techniques working at intervals of 1 °C (with temperature control to 0.002 °C) in the range 2-92 °C, and the gradual drop is in each case found to break up into two short and sharp steps. The results have an accuracy to the order of 0.2% in /κ and indicate the presence of two regular series of steps, out of phase with each other by a slowly varying temperature difference. To study the possible effects of impurities on these phenomena, the experiments have been repeated with three different grades of ethylene glycol, namely (i) commercial grade, (ii) technical grade and (iii) laboratory reagent grade. The graph for the purest grade, (iii), exhibits pairs of steps of equal height, Δ/κ similar 100, while that for (i) shows some large irregularities and the curve for (ii) shows only small deviations from regularity. This confirms the general reproducibility of the phenomena and establishes that they are characteristic of pure ethylene glycol. The refined graphs for glycol now show several similarities with those for water, and quantitative and graphical comparison indicates that /κ for water runs very close to 0.6 × /κ for ethylene glycol, both in regard to the temperatures at the discontinuities and the values of the energy jumps, so that the phenomena are to be associated with the two effective OH groups in ethylene glycol and water. A tentative quantitative interpretation is attempted on the basis of existing theories of molecular association, with some measure of success. Data on other related liquids are being obtained for further elucidation.