Effect of ethanol addition upon the structure and the cooperativity of the water H bond network Original Research Article

Density and water self-diffusion in ethanol-water mixtures are measured as a function of the temperature and for several alcohol concentrations in the water rich region. An extension of the five species model for liquid water, in which H bond cooperativity is taken into account, is proposed to interpret the temperature and concentration trends of the mixture density, solvent self-diffusion and near infrared spectra. This approach allowed us to extract some significant parameters characteristic of the solvent water H bond network such as the probability of forming H bonds, the degree of cooperativity, the supercooling and superheating limit temperatures and the distribution of water molecules among the five species. The emerging picture suggests that alcohol acts upon the water H bond network as a structure maker in the normal temperature region and, probably, as a structure breaker in the supercooled one. Moreover, a progressive disappearance of the H bond network cooperativity is observed as the alcohol concentration is increased.