Temperature dependent dynamics in water-ethanol liquid mixtures

Temperature dependent hydrogen bond energetics and dynamical features, such as the diffusion coefficient and re-orientational times, have been determined for ethanol-water mixtures with 10, 20 and 30 mol% of ethanol. Concerning pairwise interaction energies between molecules, it is found that water-water interactions become stronger, while ethanol-ethanol ones become significantly weaker in the mixtures, than the corresponding values characteristic to the pure substances. Concerning the diffusion processes, for all concentrations the activation barrier of water and ethanol molecule become very similar to each other. Re-orientational motions of water and ethanol become slower as ethanol concentration is increasing. Characteristic re-orientational times of water in the mixtures are substantially longer than these values in the pure substance. On the other hand, this change for ethanol is only moderate. Re-orientational motions of water (especially the ones related to the H-bonded interaction) become very similar for those of ethanol in the mixtures.