  Aqueous mixtures of 1-propanol have been investigated by high-energy
synchrotron X-ray diffraction upon cooling. X-ray weighted total scattering
structure factors of 6 mixtures, from 8 mol% to 89 mol% alcohol content, as
well as that of pure 1-propanol are reported from room temperature down to the
freezing points of the liquids. Molecular dynamics simulations have been
performed, in order to interpret measured data. The all atom OPLS-AA potential
model was used for 1-propanol, combined with both the SPC/E and the TIP4P/2005
water models: both combinations provide a semi-quantitative description of the
measured total structure factors at low and high alcohol contents, while the
agreement is qualitative for the mixture with 71 mol% of 1-propanol. From the
simulated particle configurations, partial radial distribution functions were
calculated. Furthermore, detailed description of the hydrogen bonded network is
provided, in terms of hydrogen bond numbers, analysis of proton donor-acceptor
ratios, size distributions of hydrogen bonded clusters and ring size
statistics. Strong temperature dependence of the percolation threshold, as well
as of the participation of the number of doubly hydrogen bonded molecules in
cyclic entities, has been found for the mixture with 89 mol% of 1-propanol.
Above an alcohol content of 20 mol%, 5-fold rings are the most frequent cyclic
entities, with a strong temperature dependence in terms of the number of rings.

Chemical Physics;Soft Condensed Matter