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
SN - 0021-9606
VL - 121
SP - 12457
EP - 12464
JO - The Journal of Chemical Physics
JF - The Journal of Chemical Physics
IS - 24
ER -