Large-Angle X-ray Scattering Investigation of the Structure of 2-Propanol–Water Mixtures (original) (raw)
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physica status solidi (b)
The structure factor of pure 1-propanol, 2-propanol and mixtures of 1-propanol/water and 2propanol/water, as a function of composition, has been determined experimentally and by molecular dynamics simulations. The primary aim was to find interatomic potentials that reproduce measured structural data at the highest possible level. For this reason, various alcohol potential models have been employed, including united atom (UA) and all atom (AA) types, in combination with a TIP4P-based model for water. In order to improve agreement with experimental values of the dielectric constant and mass density, a new UA force field for the alcohols has also been constructed. In terms of structural properties the AA model reproduces experimental results better than any of the UA models for all compositions.
Journal of Electron Spectroscopy and Related Phenomena, 2004
We have examined the influence of the intermolecular interaction on the local electronic structure by using X-ray absorption and emission spectra of liquid methanol, water, and their mixtures (in molar ratios of 9:1 and 7:3). We find a strong involvement of hydrogen bonding in the mixing of water and methanol molecules. The local electronic structure of water and methanol clusters, where water cluster is bridging within a 6-member open-ring structured methanol cluster, is separately determined. The experimental findings suggest an incomplete mixing of water-alcohol systems and a strong self-association between methanol chain and water cluster through hydrogen bonding. The enhancement of joint water-methanol open-ring structure owes the explanation to the loss of entropy of the aqueous solutions.
Journal of Molecular Liquids, 2021
Synchrotron X-ray diffraction measurements have been conducted on aqueous mixtures of propan-2ol (a.k.a. isopropanol, or 2-propanol), for alcohol contents between 10 and 90 molar %, from room temperature down to 230 K. Molecular dynamics simulations, by using an all-atom parametrization of the propan-2-ol molecule and the well-known TIP4P/2005 water model, were able to provide semi-quantitative descriptions of the measured total structure factors. Various quantities related to hydrogen bonding, like hydrogen bond numbers, size distribution of cyclic entities and cluster size distributions, have been determined from the particle coordinates obtained from the simulations. The percolation threshold at room temperature could be estimated to be between isopropanol concentrations of 62 and 74 molar %, whereas at very low temperature, calculations yielded a value above 90 molar %.
Small-angle X-ray scattering study of fluctuations in 1-propanol-water and 2-propanol-water systems
Journal of Physical Chemistry, 1990
Small-angle X-ray scattering (SAXS) measurements have been carried out on the I-propanol (NPA)-water system and on the 2-propanol (1PA)-water system at 20 OC. In the NPA-water system, the zero angle intensity, the concentration fluctuation, the Kirkwood-Buff parameters, and Debye's correlation lengths have been determined at various concentrations. In the IPA-water system, the zero angle intensity and Debye's correlation lengths have also been determined. In both the NPA-water and IPA-water systems, all obtained parameters have maxima at about 0.2 of the mole fraction of alcohol. In terms of these parameters, the mixing state of the NPA-water and IPA-water systems is discussed and compared with that of the TBA-water system.
The Journal of chemical physics, 2016
While methanol and ethanol are macroscopically miscible with water, their mixtures exhibit negative excess entropies of mixing. Despite considerable effort in both experiment and theory, there remains significant disagreement regarding the origin of this effect. Different models for the liquid mixture structure have been proposed to address this behavior, including the enhancement of the water hydrogen bonding network around the alcohol hydrophobic groups and microscopic immiscibility or clustering. We have investigated mixtures of methanol, ethanol, and isopropanol with water by liquid microjet X-ray absorption spectroscopy on the oxygen K-edge, an atom-specific probe providing details of both inter- and intra-molecular structure. The measured spectra evidence a significant enhancement of hydrogen bonding originating from the methanol and ethanol hydroxyl groups upon the addition of water. These additional hydrogen bonding interactions would strengthen the liquid-liquid interaction...
Journal of Physical Chemistry A, 2022
Structural properties of 2-butanol aqueous solutions at different concentrations have been studied using small-and wide-angle Xray scattering and molecular dynamics simulations. The experimental structure factors have been accurately reproduced by the simulations, allowing one to explain their variation with concentration and to achieve a detailed description of the structural and dynamic properties of the studied systems. The analysis of experimental and computational data has shown that 2-butanol, the simplest aliphatic chiral alcohol, tends to form aggregates at a concentration above 1 M, affecting also both the structural and dynamic properties of the solvent.
The Journal of Physical Chemistry B, 2008
Differential scanning calorimetry (DSC) has been performed on aqueous mixtures of three diols, which involve a linear carbon chain, HO-(CH 2 ) n -OH (n ) 3, 4, and 5), over the whole mole fraction range of diols. The DSC results have shown the alkyl chain parity for the freezing process of the aqueous mixtures: aqueous mixtures of 1,3-propanediol (PrD) and 1,5-pentanediol (PeD) are kept in the supercooled state or vitrified over a wide mole fraction range, while those of 1,4-butanediol (BuD) are easily crystallized. The structure of PrD-water mixtures has been elucidated by using the large-angle X-ray scattering (LAXS) technique. It has been suggested that the structural change of PrD-water mixtures occurs at PrD mole fractions of x PrD ) 0.4 and 0.8: in the range of x PrD e 0.4 where the tetrahedral-like structure of water predominates, in the range of 0.4 < x PrD < 0.8 where both PrD and water structures coexist, and in the range of x PrD g 0.8 where the inherent structure of PrD is mainly formed. 17 O and 1 H NMR relaxation measurements have been made on aqueous mixtures of ethylene glycol (EG, n ) 2), PrD, and BuD to clarify the dynamics of H 2 17 O and diol molecules. The 17 O NMR relaxation rates have suggested that the rotational motion of water molecules is gradually retarded in the diol-water mixtures with increasing diol content and that the restriction of the motion is more remarkable in the order of EG < PrD < BuD. On the basis of all the results, together with comparison with those of methanol-water, ethanol-water, and 1-propanol-water mixtures previously reported, the mixing state of diol-water mixtures has been discussed at the molecular level.
Journal of Molecular Liquids, 2020
Methanol-water liquid mixtures have been investigated by high-energy synchrotron X-ray and neutron diffraction at low temperatures. We are thus able to report the first complete sets of both X-ray and neutron weighted total scattering structure factors over the entire composition range (at 12 different methanol concentrations (xM) from 10 to 100 mol%) and at temperatures from ambient down to the freezing points of the mixtures. The new diffraction data may later be used as reference in future theoretical and simulation studies. Measured data are interpreted by molecular dynamics simulations, in which the all atom OPLS/AA force field model for methanol is combined with both the SPC/E and TIP4P/2005 water potentials. Although the TIP4P/2005 water model was found to be somewhat more successful, both combinations provide at least semi-quantitative agreement with measured diffraction data. From the simulated particle configurations, partial radial distribution functions, as well as various distributions of the number of hydrogen bonds have been determined. As a general trend, the average number of hydrogen bonds increases upon cooling. However, the number of hydrogen bonds between methanol molecules slightly decreases with lowering temperatures in the concentration range between ca. 30 and 60 mol % alcohol content. The same is valid for water-water hydrogen bonds above 70 mol % of methanol content, from room temperature down to 193 K.
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.