ISOTOPIC-SUBSTITUTION EFFECTS ON THE VOLUMETRIC AND VISCOSIMETRIC PROPERTIES OF WATER-DIMETHYLSULFOXIDE MIXTURES AT 25-DEGREES-C

Densities and viscosities of binary mixtures (H2O or D2O) (1) + (DMSO or DMSO-D6)(2) have been measured over the entire mole fraction range; and the excess volumes, excess viscosities, and excess partial molar volumes V-l(E) of the components have been obtained. All systems show negative excess volume V-E at all compositions, values for mixtures co ntaining D2O being more negative than those with H2O by ca. 0.03 cm(3) -mol(-1) at x(1) = 0.6, where a minimum is observed. The difference be tween DMSO and DMSO-D6 containing mixtures is negligible. The excess v iscosity eta(E) is always positive and shows a maximum at x(1) = 0.65; at this composition, the substitution of H2O with D2O causes an exces s viscosity increment of ca. 0.35 mPa-s, while deuteration of DMSO bri ngs about a smaller increase, ca. 0.1 mPa-s. The trend of V-2(E) with concentration shows the characteristic features of moderately hydropho bic solutes in water (negative values and a minimum in the water-rich region), features that are slightly but significantly more marked in D 2O than in H2O. The V-l(E) values in the water-diluted region and at x (1) = 0 are more negative for D2O than for H2O.