Single-particle dynamics in dimethyl-sulfoxide/water eutectic mixture by neutron scattering

Citation
Jt. Cabral et al., Single-particle dynamics in dimethyl-sulfoxide/water eutectic mixture by neutron scattering, J CHEM PHYS, 113(19), 2000, pp. 8736-8745
Citations number
58
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF CHEMICAL PHYSICS
ISSN journal
00219606 → ACNP
Volume
113
Issue
19
Year of publication
2000
Pages
8736 - 8745
Database
ISI
SICI code
0021-9606(20001115)113:19<8736:SDIDEM>2.0.ZU;2-6
Abstract
We study water and dimethyl-sulfoxide (DMSO) dynamics in the eutectic DMSO/ water mixture, 2H(2)O:1DMSO, by incoherent quasielastic and inelastic neutr on scattering. A temperature range from room down to -27 degreesC is invest igated. Both water and DMSO translational dynamics are significantly slowed in the mixture compared to pure liquids. They exhibit different diffusion dynamics, pointing to the absence of stable hydrogen bonded complexes. Furt her, the presence of a solute suppresses the dynamic anomalies of water: se lf-diffusion coefficients for water in the mixture, as well as residence ti mes for jump diffusion reveal an Arrhenius temperature dependence, in contr ast to the strong non-Arrhenius behavior in pure water. The density of vibr ational states shows a shift of the characteristic librational peak in pure water towards higher energies in the mixture, reflecting hindrance of larg e amplitude proton motions. These results are compatible with computer simu lations which predict longer hydrogen-bond lifetimes in the mixture, compar ed to pure water. However, rotational relaxation times for water protons in the mixture are estimated to be similar to1 ps, as for pure water. This ex perimental finding suggests that unlike in pure, low temperature water, pro ton librations should no longer be the main mechanism responsible for hydro gen-bond breaking in the mixture. Thus, the correspondence between the prot on hindered rotational relaxation time and the "hydrogen-bond lifetime" sho uld not apply in DMSO-water mixtures. (C) 2000 American Institute of Physic s. [S0021-9606(00)51242-2].