Local structural effects and related dynamics in supercritical ethanol. 2. Hydrogen-bonding network and its effect on single reorientational dynamics

Abstract

The local hydrogen-bonding (HB) network and its possible interconnection with the single reorientational dynamics in pure supercritical (sc) ethanol have been systematically investigated by employing molecular dynamics simulation techniques. The results obtained reveal a nonlinear density dependence of the calculated average number of hydrogen bonds 〈nHB〉, similar to that of the calculated coordination numbers Nc, signifying also the interrelation between the local HB network and the local density augmentation in sc ethanol. Additionally, the HB dynamics were investigated in terms of several appropriate time correlation functions. The results obtained reveal that the density dependence of HB dynamics has some similarities with local density and residence dynamics, corresponding to very short length scales. Moreover, the effect of mutual reorientation on HB dynamics seems to be more important than that of mutual diffusion. Finally, the reorientational dynamics of several intramolecular vectors of ethanol have been systematically studied. From the results obtained, we may observe that the dynamics of several reorientational modes in the molecule exhibit significant differences between them. Furthermore, the effect of the HB state of each molecule on these dynamics has also been studied, revealing significant differences, especially in the case of the dynamics of HB free molecules.