engleski

Structural organization in alcohol solutions

In a similar manner as the large molecules containing non-polar and polar regions adopt complex self- assemblies, small molecules as alcohols in the water environment, holding the same amphipatic property, also form rich types of association. Moreover, alcohol-water mixtures, exhibit micro-heterogeneity or local immiscibility of the components. Structural specificity is also shown through non trivial concentration dependence, which is usually connected to the three structural regimes: strong water clustering ; bi-continuous phase of water and alcohol clusters ; and alcohol-rich cluster domain. However, no clear or unambiguous description of these phenomena yet exist. In our study, we use molecular dynamic simulations to access structural properties on the level of the atomic scale. Extensive simulations of concentration dependence were done for three systems: methanol-water, ethanol-water and methanol-acetone. In addition to thermodynamic, static and dynamic properties such as radial distribution functions (RDFs), cluster size distributions and velocity correlations, we also analyzed the pair connectedness function or radial distribution functions of clusters, which to our knowledge have not yet been reported for these systems. We show that connectedness functions offer better insight in the global structural organization. The most intriguing result is that regimes defined by the change of the behavior in cluster RDFs can be compared to the extreme values in the concentration dependence for example of the heat of mixing and sound propagation.

alcohol solutions; structure; clusters; molecular dynamics

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