Pressure dependence on the single-particle dynamics and hydrogen-bond structural relaxation of water–DMSO mixtures under ambient and cold conditions

Abstract

The effects of pressure on the single-particle translational and rotational dynamics and the hydrogen-bond structural relaxation of water–dimethyl sulfoxide (DMSO) mixtures were investigated under ambient and cold conditions using classical molecular dynamics simulations. We considered five different concentrations of DMSO with mole fractions X _DMSO = 0.012, 0.09, 0.20, 0.35, and 0.50 and seven different pressures ranging from 0.1 to 500 MPa. It was found that the addition of DMSO to water leads to slow dynamics for both water and DMSO molecules under pressure. At very low concentrations of DMSO, water exhibits anomalous behavior with the application of pressure at 258 K, whereas DMSO molecules exhibit average pressure dependencies. The formation of strong hydrogen bonds between water and DMSO molecules occurs when DMSO is added to water, but the extended network is altered due to the absence of any hydrogen-bond donating ability of DMSO. Our calculated water–water and DMSO–water hydrogen-bond structural relaxation times show an initial decrease with the application of pressure at 258 K for solutions with low DMSO concentrations. However, at higher concentrations of DMSO, the relaxation times increase, on average, and no anomalous behavior of the dynamical properties is found on the application of pressure.

Keywords:

• water–DMSO mixture
• self-diffusion coefficients
• orientational relaxation times
• hydrogen bonds structural relaxation times

Acknowledgements

One of the authors (S. Chowdhuri) would like to thank Prof. Amalendu Chandra for his kind support and many helpful communications. The authors are grateful to the CSIR for financial support of this work through grant No. 01 (2352)/09 EMR-II and also to the Indian Institute of Technology, Bhubaneswar, for the initial help in executing this project.