Temperature-dependent structure of 1-propanol/water mixtures: X-ray diffraction experiments and computer simulations at low and high alcohol contents

• Published in: Journal of molecular liquids 2021-10, Vol.340, p.117188, Article 117188
• Main Authors: Pethes, Ildikó, Pusztai, László, Ohara, Koji, Temleitner, László
• Format: Article
• Language: English
• Subjects: 1-Propanol-water mixtures; Hydrogen bonded network; Molecular dynamics simulation; Temperature dependence; X-ray diffraction
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2021.117188

•Systematic X-ray diffraction studies over the entire concentration range, from room temperature down to the freezing point.•Molecular dynamics simulations with OPLS/AA, TIP4P2005 and SPC/E potentials for interpreting experimental data.•Detailed description of the H-bonded network: H-bond numbers, cluster size distributions, ring statistics.•H-bonded network is percolating for xP ≤ 0.71 at all examined temperature and for xP = 0.89 at T ≤ 273 K.•5-fold rings are the most frequent cyclic entities for xP ≥ 0.2. 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.