E-Mails:

This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (

In this paper, the dielectric properties of water-dimethylsulfoxide (DMSO) mixtures with different mole ratios have been investigated in the range of 1 GHz to 40 GHz at 298 K by using a molecular dynamics (MD) simulation. Only one dielectric loss peak was observed in the frequency range and the relaxation in these mixtures can be described by a single relaxation time of the Davidson-Cole. It was observed that within experimental error the dielectric relaxation can be described by the Debye-like model (

Over the past few years, the use of microwave heating for promoting organic chemical transformations has been widely accepted by scientists [

Dimethylsulfoxide (DMSO) and its mixtures with other solvents (particularly water) have aroused much interest among scientists in the last decades [_{2}O) was formed under certain conditions [

In fact, the long-standing interest in all mixed solvents is largely due to their importance as tunable reaction media. The dielectric constant and the relaxation time, as well as the refractive indexes and other transport properties of mixed solvents, can be conveniently tuned by changing the composition [

A dielectric study of DMSO-water using molecular dynamics simulation (MD) is introduced in this paper. The static dielectric constant _{0}, dielectric constant at high frequency _{∞}, the relaxation time τ, the Cole-Cole curve and the complex permittivity spectrum have been obtained.

The mixtures with DMSO mole fractions _{DMSO}_{D}_{i}_{j}_{ij}_{ij}_{i}_{i}_{i}

Simulations reported in this paper were run in the NVT ensemble on systems consisting of a thousand molecules placed in a cubic box with periodic boundary conditions at an average temperature of 298 K. The box length was chosen to match the experimental density of DMSO-water mixtures solvent at 298 K. The Lennard-Jones forces were cut off at half of the box length and long-range Coulomb interactions were treated using the Ewald sum method [

To calculate the effective dielectric constant of a complex solute from computer simulation, it is necessary to map the properties of the solute observed in the simulation onto a simpler geometry, one amenable to analytical treatment. Specifically, the solute is approximated as a spherical cavity of volume _{RF}_{RF}_{0} is the dielectric constant of vacuum, _{B}

Thermodynamic and statistical perturbation theory originally developed by Zwanzig [

The composition dependence of the calculated values of Δ

Eyring _{B}

The mixture’s overall dielectric relaxation time

In

The complex permittivities are fitted by the nonlinear least-squares fit method to the Havriliak-Negami expression to obtain various dielectric parameters:
_{∞} is the permittivity at high frequency, _{∞} is the static dielectric constant,

For the Debye Equation, the real

Permittivity and losses for DMSO-water mixtures at 298 K are shown in _{D}

From

This paper presents the picosecond dynamical profile of water-DMSO solutions over the entire range of composition. The static dielectric constant, dielectric relaxation in the frequency of microwave, as well as the microwave spectra of DMSO-water mixtures have been investigated through molecular dynamics simulation at room conditions, and this simulation has been proved to be an efficient tool for the study of molecular processes in solutions under the sufficiently wide frequency range.

This project is supported by the National Science Foundation of China under Grant NO.60531010 and Research Fund for the Doctoral Program of Higher Education of China under Grant NO. 20070610120.

MD (full symbols) and Reference [

Free energy change of activation via water-DMSO solutions vs. mole fractions.

Mole fraction dependence of the relaxation time

Permittivities and losses for DMSO-water mixtures at various concentrations at 298 K. (a) The real vs. frequency. (b) The imaginary vs. frequency.

The Cole-Cole curve of DMSO-water mixture at various concentrations.

L-J parameters and partial charges for water and DMSO.

^{−1}) |
|||
---|---|---|---|

O(water) | 0.65 | 0.3165 | −0.82 |

H(water) | 0.0 | 0.0 | 0.41 |

| |||

O(DMSO) | 0.30 | 0.28 | −0.459 |

S | 1.00 | 0.34 | 0.139 |

CH_{3} |
1.23 | 0.38 | 0.16 |

Compositions of the DMSO-water mixtures. Solvent 1 is DMSO; solvent 2 is water; _{i}_{i}_{D}

_{1} |
_{2} |
_{1} |
_{2} |
^{3}) |
_{D} | ||
---|---|---|---|---|---|---|---|

1 | 0.1 | 0.9 | 100 | 900 | 34.05 | 1.0105 |
1.3458 |

2 | 0.21 | 0.79 | 210 | 790 | 36.76 | 1.0242 |
1.3600 |

3 | 0.35 | 0.65 | 350 | 650 | 39.0 | 1.0927 | 1.4385 |

4 | 0.48 | 0.52 | 480 | 520 | 41.38 | 1.0983 | 1.4525 |

5 | 0.91 | 0.09 | 910 | 90 | 47.93 | 1.0965 | 1.4741 |

Reference [

Reference [