Effect of Ethanol Addition Upon the Structure and the Cooperativity of Thewater H Bond Network (original) (raw)
Related papers
The Journal of Physical Chemistry B
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.
Variations of the Hydrogen Bonding and Hydrogen-Bonded Network in Ethanol–Water Mixtures on Cooling
The Journal of Physical Chemistry B, 2018
Extensive molecular dynamics computer simulations have been conducted for ethanol-water liquid mixtures in the water-rich side of the composition range, with 10, 20 and 30 mol % of the alcohol, at temperatures between room temperature and the experimental freezing point of the given mixture. All-atom type (OPLS) interatomic potentials have been assumed for ethanol, in combination with two kinds of rigid water models (SPC/E and TIP4P/2005). Both combinations have provided excellent reproductions of the experimental X-ray total structure factors at each temperature; this provided a strong basis for further structural analyses. Beyond partial radial distribution functions, various descriptors of hydrogen bonded assemblies, as well as of the hydrogen bonded network have been determined from the simulated particle configurations. A clear tendency was observed towards that an increasing proportion of water molecules participate in hydrogen bonding with exactly 2 donor-and 2 acceptor sites as temperature decreases. Concerning larger assemblies held together by hydrogen bonding, the main focus was put on the properties of cyclic entities: it was found that, similarly to methanolwater mixtures, the number of hydrogen bonded rings has increased with lowering temperature. However, for ethanol-water mixtures the dominance of not the six-, but of the five-fold rings could be observed.
Ethanol and water capacities of alcohols: A molecular dynamics study
Chemical Engineering Science, 2006
The extended hydrogen bond networks formed by alcohols are good indicators of their capacities to hold water. Results from molecular dynamics simulations on 24 linear alcohol isomers containing 6-12 carbon atoms show the effects of hydroxyl location on bulk hydrogenbonded structures. Calculated oxygen-oxygen radial distributions obtained from simulations were correlated to experimental liquid-liquid solvent extraction studies involving ternary water/ethanol/alcohol systems. It was found that hydroxyl group location determines the primary structure of the bulk alcohol's hydrogen bond network and that an alcohol's capacity for water correlates directly to the size of this network.
Chemical Physics Letters, 2003
Molecular dynamics simulations have been performed for water-tertiary butyl alcohol (TBA) mixtures in the water rich region. Examination of the Kirkwood-Buff integrals, local composition, and potential mean force for concentration in the range 0.05-0.07 TBA mole fraction leads to insight into the unexpected behaviors of some thermodynamics properties. Hydrophobic hydration phenomena and solvent-solute association are discussed at the molecular level. Since the hydrogen bond network elasticity modulus is a quantitative measure of the resistance of the water hydrogen bonds network to external perturbation arising from solvent-solute interactions, a first principle calculation of the elasticity modulus was carried out.
Structural transition in alcohol-water binary mixtures: A spectroscopic study
Journal of Chemical Sciences, 2008
The strengthening of the hydrogen bonding (H-bond) network as well as transition from the tetrahedral-like water network to the zigzag chain structure of alcohol upon increasing the alcohol concentration in ethanol-water and tertiary butanol (TBA)-water mixtures have been studied by using both steady state and time resolved spectroscopy. Absorption and emission characteristics of coumarin 153 (C153), a widely used non-reactive solvation probe, have been monitored to investigate the structural transition in these binary mixtures. The effects of the hydrogen bond (H-bond) network with alcohol concentration are revealed by a minimum in the peak frequency of the absorption spectrum of C153 which occur at alcohol mole fraction ~0⋅10 for water-ethanol and at ~0⋅04 for water-TBA mixtures. These are the mole fractions around which several thermodynamic properties of these mixtures show anomalous change due to the enhancement of H-bonding network. While the strengthening of H-bond network is revealed by the absorption spectra, the emission characteristics show the typical non-ideal alcohol mole fraction dependence at all concentrations. The time resolved anisotropy decay of C153 has been found to be bi-exponential at all alcohol mole fractions. The sharp change in slopes of average rotational correlation time with alcohol mole fraction indicates the structural transition in the environment around the rotating solute. The changes in slopes occur at mole fraction ~0⋅10 for TBA-water and at ~0⋅2 for ethanol-water mixtures, which are believed to reflect alcohol mole fraction induced structural changes in these alcohol-water binary mixtures.
Hydrogen-bond networks in linear, branched and tertiary alcohols
Chemical Engineering Science, 2007
Molecular dynamics simulations are used to determine the hydrogen-bond networks formed by 54 linear and branched alcohols containing 5-20 carbon atoms, and the results show systematic differences in their hydrogen-bonded structures, depending both on hydroxyl group position and the alcohol's molecular weight. The hydrogen-bonded networks within these pure solvents correspond with experimentally determined water capacities for solvents in four main structural classes. These categories are: primary alcohols, secondary alcohols, tertiary alcohols, and alcohols with the branching point removed from the hydroxyl group. Each of these structural classes exhibits unique behavior in the correlation between the extended hydrogen-bond networks and observed capacities for water.
Hydrogen bond network topology in liquid water and methanol: a graph theory approach
Physical chemistry chemical physics : PCCP, 2013
Networks are increasingly recognized as important building blocks of various systems in nature and society. Water is known to possess an extended hydrogen bond network, in which the individual bonds are broken in the sub-picosecond range and still the network structure remains intact. We investigated and compared the topological properties of liquid water and methanol at various temperatures using concepts derived within the framework of graph and network theory (neighbour number and cycle size distribution, the distribution of local cyclic and local bonding coefficients, Laplacian spectra of the network, inverse participation ratio distribution of the eigenvalues and average localization distribution of a node) and compared them to small world and Erd + os-Rényi random networks. Various characteristic properties (e.g. the local cyclic and bonding coefficients) of the network in liquid water could be reproduced by small world and/or Erd + os-Rényi networks, but the ring size distribution of water is unique and none of the studied graph models could describe it. Using the inverse participation ratio of the Laplacian eigenvectors we characterized the network inhomogeneities found in water and showed that similar phenomena can be observed in Erd + os-Rényi and small world graphs. We demonstrated that the topological properties of the hydrogen bond network found in liquid water systematically change with the temperature and that increasing temperature leads to a broader ring size distribution. We applied the studied topological indices to the network of water molecules with four hydrogen bonds, and showed that at low temperature (250 K) these molecules form a percolated or nearly-percolated network, while at ambient or high temperatures only small clusters of four-hydrogen bonded water molecules exist. † Electronic supplementary information (ESI) available: : the fraction of bonds between molecules with different numbers of hydrogen bonds; : the histogram of the local bonding coefficient (r b ) for the investigated systems; : spectral density of the Laplace matrix for the investigated systems; : the histogram of the local cyclic coefficient (r c ) for the low-density patch of water at various temperatures (in K). See
How can we detect hydrogen bond local cooperativity in liquid water: A simulation study
Journal of Molecular Liquids, 2017
The significant cooperative effect between water molecules substantially affects the properties of liquid water. The cooperativity of hydrogen bonds means that the hydrogen bond strength is influenced by the neighboring water molecules. Another descriptor related to cooperativity is degree correlation (or static correlation) describing the probability of hydrogen-bonded molecule pairs participating in additional hydrogenbonds. Herein we analyze the latter one in liquid water at various temperatures and densities in a series of molecular dynamics simulations with the help of knowledge from network science. We investigated how the applied hydrogen bond criteria (energetic or geometric) influence the obtained results, and showed that the energetic criterion is much more rigorous and reliable, therefore should be used for similar studies. We found that the structure of the subsystems of water molecules with 3 and 4 hydrogen-bonds is distinctly different at low temperature, 3-hydrogen-bonded water molecules form branched chain structures at all temperature. Deconvolution of the descriptors of the mixing pattern of water molecules according to their donor and acceptor numbers showed that species with complementary hydrogen bonding properties are likely to correlate and form H-bonds with each other, while species with similar H-bond pattern tend to avoid each other. Pearson's coefficient (global descriptor of the local cooperativity) of the studied networks suggests that at normal density the H-bonded network in liquid water can be described by an uncorrelated network.