New X-ray and neutron
diffraction experiments have been performed
on ethanol–water mixtures as a function of decreasing temperature,
so that such diffraction data are now available over the entire composition
range. Extensive molecular dynamics simulations show that the all-atom
interatomic potentials applied are adequate for gaining insight into
the hydrogen-bonded network structure, as well as into its changes
on cooling. Various tools have been exploited for revealing details
concerning hydrogen bonding, as a function of decreasing temperature
and ethanol concentration, like determining the H-bond acceptor and
donor sites, calculating the cluster-size distributions and cluster
topologies, and computing the Laplace spectra and fractal dimensions
of the networks. It is found that 5-membered hydrogen-bonded cycles
are dominant up to an ethanol mole fraction
x
eth
= 0.7 at room temperature, above which the concentrated
ring structures nearly disappear. Percolation has been given special
attention, so that it could be shown that at low temperatures, close
to the freezing point, even the mixture with 90% ethanol (
x
eth
= 0.9) possesses a three-dimensional (3D)
percolating network. Moreover, the water subnetwork also percolates
even at room temperature, with a percolation transition occurring
around
x
eth
= 0.5.