Hydrogen Bonding and Dielectric Spectra of Ethylene Glycol-Water Mixtures from Molecular Dynamics Simulations (original) (raw)
Related papers
2018
The dielectric response of fluids to electromagnetic radiation in the microwave region originates from processes occurring at the molecular level. Understanding these processes in more detail is relevant to many fields, such as microwave heating, fluid mixing, and separation technologies. In this work, we use molecular dynamics (MD) simulations to study the dielectric spectra of ethanol/water mixtures. We compare our predictions with experimental results at different compositions. We show how the dielectric response can be estimated to a high level of accuracy using three dielectric relaxations: a dominant and slower process at microwave frequencies and two faster processes. A deeper study of the dynamics of the hydrogen bond network formed in these systems reveals how collective processes between the individual species are the origin of the final dielectric response. Our results agree with the “wait-and-switch” mechanism, which describes the dynamics of the hydrogen bond network as...
The journal of physical chemistry. B, 2018
The dielectric response of fluids to electromagnetic radiation in the microwave region originates from processes occurring at the molecular level. Understanding these processes in more detail is relevant to many fields, such as microwave heating, fluid mixing, and separation technologies. In this work, we use molecular dynamics (MD) simulations to study the dielectric spectra of ethanol/water mixtures. We compare our predictions with experimental results at different compositions. We show how the dielectric response can be estimated to a high level of accuracy using three dielectric relaxations: a dominant and slower process at microwave frequencies and two faster processes. A deeper study of the dynamics of the hydrogen bond network formed in these systems reveals how collective processes between the individual species are the origin of the final dielectric response. Our results agree with the "wait-and-switch" mechanism, which describes the dynamics of the hydrogen bond ...
Condensed Matter Physics, 2015
We have investigated thermodynamic and dynamic properties as well as the dielectric constant of water-methanol model mixtures in the entire range of composition by using constant pressure molecular dynamics simulations at ambient conditions. The SPC/E and TIP4P/Ew water models are used in combination with the OPLS united atom modelling for methanol. Changes of the average number of hydrogen bonds between particles of different species and of the fractions of differently bonded molecules are put in correspondence with the behavior of excess mixing volume and enthalpy, of self-diffusion coefficients and rotational relaxation times. From the detailed analyses of the results obtained in this work, we conclude that an improvement of the description of an ample set of properties of water-methanol mixtures can possibly be reached, if a more sophisticated, carefully parameterized, e.g., all atom, model for methanol is used. Moreover, exploration of parametrization of the methanol force field, with simultaneous application of different combination rules for methanol-water cross interactions, is required.
Journal of Molecular Liquids, 2014
Molecular dynamics simulations of liquid ethylene glycol described by the OPLS-AA force field were performed to gain insight into its hydrogen-bond structure. We use the population correlation function as a statistical measure for the hydrogen-bond lifetime. In an attempt to understand the complicated hydrogen-bonding, we developed new molecular visualization tools within the Vish Visualization shell and used it to visualize the life of each individual hydrogen-bond. With this tool hydrogen-bond formation and breaking as well as clustering and chain formation in hydrogen-bonded liquids can be observed directly. Liquid ethylene glycol at room temperature does not show significant clustering or chain building. The hydrogen-bonds break often due to the rotational and vibrational motions of the molecules leading to an H-bond half-life time of approximately 1.5 ps. However, most of the H-bonds are reformed again so that after 50 ps only 40% of these H-bonds are irreversibly broken due to diffusional motion. This hydrogenbond half-life time due to diffusional motion is 80.3 ps. The work was preceded by a careful check of various OPLS-based force fields used in the literature. It was found that they lead to quite different angular and H-bond distributions.
Dielectric Relaxation Studies of Binary Liquid Mixtures of a few Glycols with 1, 4-Dioxane
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The dielectric relaxation and dipole moment of different concentration binary mixtures of Ethylene glycol, Propylene glycol and Butylene glycol with dilute solutions of 1,4-Dioxane at 33°C. The dielectric relaxation of binary mixtures of polar liquids in non polar solvents at microwave frequencies has been attempted such studies provide meaningful information regarding intermolecular and intramolecular association between the solutes and solvent molecules. The static dielectric constants (e 0 ) of glycols like ethylene glycol, propylene glycol and butylene glycol in dilute solutions of 1,4-Dioxane were determined at 303K. The measuring frequency of the dipole meter was 2MHz. Xband and J-band microwave benches operating at 9.52GHz and 7.72GHz were used for determination dielectric permittivity (e¢) and dielectric loss factor (e²). The values of molecular relaxation time (t 0 ) and dipole moment (m) for the different composition of binary mixtures are determined. The comparative values of relaxation time (t 0 ) of the two bands (X-Band) and (J-Band) for various binary mixture molecular conformation of these system.
Collective contributions to the dielectric relaxation of hydrogen-bonded liquids
The Journal of Chemical Physics, 2004
Dielectric relaxation times are often interpreted in terms of the reorientation of dipolar species or aggregates. The relevant time correlation function contains, however, cross terms between dipole moments of different particles. In the static case, these cross terms are accounted for by the Kirkwood factor g K. Theories and molecular dynamics simulations suggest that such cross correlations may also affect the time-dependent properties, as reflected in the dielectric spectra. We present an experimental method for detecting effects of such cross correlations in dielectric spectra by a comparative analysis of dielectric and magnetic relaxation data. We demonstrate that such collective contributions can substantially affect dielectric relaxation. Experiments for n-pentanol (g K ϭ3.06 at 298 K͒ and 2,2-dimethyl-3-ethyl-pentane-3-ol (g K ϭ0.59) and their solutions in carbon tetrachloride show that in systems with g K Ͼ1, the cross correlations slow down dielectric relaxation. In systems with g K Ͻ1, dielectric relaxation is enhanced. The results conform to theoretical predictions by Madden and Kivelson ͓Adv. Chem. Phys. 56, 467 ͑1984͔͒ and to results of molecular dynamics simulations. The relaxation enhancement by cross terms in the case of g K Ͻ1 is difficult to rationalize by conventional models of dielectric relaxation.
Molecular Simulation, 2015
The response of molecular systems to electromagnetic radiation in the microwave region (0.3-300 GHz) has been principally studied experimentally, using broadband dielectric spectroscopy. However, relaxation times corresponding to reorganisation of molecular dipoles due to their interaction with electromagnetic radiation at microwave frequencies are within the scope of modern molecular simulations. In this work, fluctuations of the total dipole moment of a molecular system, obtained through molecular dynamics simulations, are used to determine the dielectric spectra of water, a series of alcohols and glycols, and monoethanolamine. Although the force fields employed in this study have principally been developed to describe thermodynamic properties, most them give fairly good predictions of this dynamical property for these systems. However, the inaccuracy of some models and the long simulation times required for the accurate estimation of the static dielectric constant can sometimes be problematic. We show that the use of the experimental value for the static dielectric constant in the calculations, instead of the one predicted by the different models, yields satisfactory results for the dielectric spectra, and hence the heat absorbed from microwaves, avoiding the need for extraordinarily long simulations or re-calibration of molecular models.
Dielectric relaxation in water–cholesterol mixture cluster: molecular dynamics simulation
Journal of Molecular Structure, 2005
Molecular dynamics (MD) studies of the cluster composed of cholesterol (C 27 H 45 OH) and water molecules are presented. We have investigated several dynamical quantities of cholesterol as a function of its concentration in the mixture cluster and the temperature. The main attention was focused on the temperature and concentration dependence of the calculated total dipole moment autocorrelation function and dielectric loss of the cluster.
Journal of Molecular Liquids, 2011
The dielectric relaxation measurements on binary mixtures of 2-methoxyethanol with water have been carried out over entire concentrations and at temperature range of 0°C to 25°C using a picosecond time domain reflectometry technique. The complex dielectric permittivity spectra of 2-methoxyethanol/water mixtures were fitted using Havriliak-Negami equation. The static dielectric constant and relaxation time for all concentrations were obtained using least square fit method. The principal relaxation time is small if compared to that of corresponding alcohol/water mixtures this may be due to the hydrogen bonding ether oxygen in the 2-ME-water system. Excess dielectric properties, Kirkwood correlation factor, thermodynamic properties and Bruggeman factor are also determined and the results are interpreted in terms of heterogeneous interactions among the unlike molecules due to hydrogen bonding.
2012
Using time domain reflectometry, the complex dielectric spectra between 10 MHz to 20 GHz has been measured in the whole composition range at 10, 20, 30 and 40 o C for the binary mixtures of ethylene glycol and dimethyl sulfoxide. For all the mixtures, only one dielectric loss peak was observed in this frequency range. The relaxation in these mixtures can be described by a single relaxation time using the Debye model. A systematic variation is observed in dielectric constant (ε0) and relaxation time (τ). The excess permittivity (ε E ), excess inverse relaxation time (1/τ) E , Kirkwood correlation factor (g) and thermodynamic parameters viz. enthalpy of activation (∆H) and Gibbs free energy of activation (∆G) have been determined, to confirm the formation of hydrogen bonded homogeneous and heterogeneous cooperative domains, the dynamics of solute -solute interaction and the hindrance to molecular rotation in the hydrogen bonded glass forming ethylene glycol -dimethyl sulphoxide system.