TY - JOUR

T1 - Quasi-elastic neutron scattering study of dimethyl-sulfoxide-water mixtures

T2 - Probing molecular mobility in a nonideal solution

AU - Bordallo, H. N.

AU - Herwig, K. W.

AU - Luther, B. M.

AU - Levinger, N. E.

PY - 2004/12/22

Y1 - 2004/12/22

N2 - The translational and rotational motions of water and dimethyl sulfoxide, [DMSO, (CH 3) 2SO] have been investigated using quasi-elastic neutron scattering. Water-DMSO mixtures at five DMSO mole fractions, χ DMSO, ranging from 0 to 0.75, were measured. Hydrogen-deuterium substitution was used to extract independently the water proton dynamics (d-DMSO-H 2O), the DMSO methyl proton dynamics (h-DMSO-D 2O) and to obtain background corrections (d-DMSO-D 2O). The translational diffusion of water slows down significantly compared to bulk water at all χ DMSO>0. The rotational time constant for water exhibits a maximum at χ DMSO=0.33 that corresponds to the observed maximum of the viscosity of the mixture. Data for DMSO can be analyzed in terms of a relatively slow tumbling of the molecule about its center-of-mass in conjunction with random translational diffusion. The rotational time constant for this motion exhibits some dependence on χ DMSO, while the translational diffusion constant shows no clear variation for χ DMSO>0. The results presented reinforce the idea that due to the stronger associative nature of DMSO, DMSO-water aggregates are formed over the whole composition range, disturbing the tetrahedral natural arrangement of the water molecules. As a consequence adding DMSO to water causes a drastic slowing down of the dynamics of the water molecule, and vice versa.

AB - The translational and rotational motions of water and dimethyl sulfoxide, [DMSO, (CH 3) 2SO] have been investigated using quasi-elastic neutron scattering. Water-DMSO mixtures at five DMSO mole fractions, χ DMSO, ranging from 0 to 0.75, were measured. Hydrogen-deuterium substitution was used to extract independently the water proton dynamics (d-DMSO-H 2O), the DMSO methyl proton dynamics (h-DMSO-D 2O) and to obtain background corrections (d-DMSO-D 2O). The translational diffusion of water slows down significantly compared to bulk water at all χ DMSO>0. The rotational time constant for water exhibits a maximum at χ DMSO=0.33 that corresponds to the observed maximum of the viscosity of the mixture. Data for DMSO can be analyzed in terms of a relatively slow tumbling of the molecule about its center-of-mass in conjunction with random translational diffusion. The rotational time constant for this motion exhibits some dependence on χ DMSO, while the translational diffusion constant shows no clear variation for χ DMSO>0. The results presented reinforce the idea that due to the stronger associative nature of DMSO, DMSO-water aggregates are formed over the whole composition range, disturbing the tetrahedral natural arrangement of the water molecules. As a consequence adding DMSO to water causes a drastic slowing down of the dynamics of the water molecule, and vice versa.

UR - http://www.scopus.com/inward/record.url?scp=22944449019&partnerID=8YFLogxK

U2 - 10.1063/1.1823391

DO - 10.1063/1.1823391

M3 - Journal article

AN - SCOPUS:22944449019

VL - 121

SP - 12457

EP - 12464

JO - The Journal of Chemical Physics

JF - The Journal of Chemical Physics

SN - 0021-9606

IS - 24

ER -