Anomalous viscoelastic response of water-dimethyl sulfoxide solution and a molecular explanation of non-monotonic composition dependence of viscosity

Kumar, Shubham and Sarkar, Sarmistha and Bagchi, Biman (2019) Anomalous viscoelastic response of water-dimethyl sulfoxide solution and a molecular explanation of non-monotonic composition dependence of viscosity. In: JOURNAL OF CHEMICAL PHYSICS, 151 (19).

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Abstract

Amphiphilic molecules such as dimethyl sulfoxide (DMSO) and its aqueous binary mixtures exhibit pronounced nonideality in composition dependence of several static and dynamic properties. We carry out detailed molecular dynamics simulations to calculate various properties including viscosity of the mixture and combine the results with a mode coupling theory analysis to show that this nonideality can be attributed to local structures that are stable on a short time scale but transient on a long time scale to maintain the large scale homogeneity of the solution. Although the existence of such quasistable structures has been deciphered from spectroscopy, a detailed characterization does not exist. We calculate stress-stress autocorrelation functions (SACFs) of water-DMSO binary mixtures. We employ two different models of water, SPC/E and TIP4P/2005, to check the consistency of our results. Viscosity shows a pronounced nonmonotonic composition dependence. The calculated values are in good agreement with the experimental results. Fourier transform of SACF provides frequency-dependent viscosity. The frequency-dependent viscosity (that is, viscoelasticity) is also found to be strongly dependent on composition. Viscoelasticity exhibits sharp peaks due to intramolecular vibrational modes of DMSO, which are also seen in the density of states. We evaluate the wavenumber dependent dynamic structure factor and wavenumber dependent relaxation time. The latter also exhibits a sharp nonmonotonic composition dependence. The calculated dynamic structure factor is used in mode coupling theory expression of viscosity to obtain a semiquantitative understanding of anomalous composition dependence of viscosity. Both the self-diffusion coefficients and rotational correlation times of water and DMSO molecules exhibit nonmonotonic composition dependence.

Item Type:	Journal Article
Publication:	JOURNAL OF CHEMICAL PHYSICS
Publisher:	AMER INST PHYSICS
Additional Information:	Copyright of this article belongs to AMER INST PHYSICS
Keywords:	HYDROGEN-BOND DYNAMICS; MODE-COUPLING THEORY; DMSO BINARY-MIXTURE; NEUTRON-DIFFRACTION; SHEAR VISCOSITY; FORCE-FIELD; LIQUID; DIMETHYLSULFOXIDE; TRANSPORT; NONIDEALITY
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	23 Jan 2020 09:33
Last Modified:	23 Jan 2020 09:33
URI:	http://eprints.iisc.ac.in/id/eprint/64345

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