Journal of Physical Chemistry, Vol.98, No.12, 3222-3225, 1994
Thermal Expansivity, Molar Volume, and Heat-Capacity of Liquid Dimethyl-Sulfoxide Water Mixtures at Subzero Temperatures
The specific volume, thermal expansivity, and specific heat capacity of liquid binary mixtures of water and dimethyl sulfoxide (DMSO) have been measured at temperatures ranging from approximately -25-degrees-C to room temperature, and at DMSO concentrations from 0 to 85% (w/w). Apparent quantities (apparent molar volume, apparent thermal expansivity, and apparent molar heat capacity) of DMSO were evaluated. Around room temperature, the concentration dependence of these functions show a behavior characteristic for aqueous solutions of molecules with nonpolar moieties. However, at the lowest temperatures the concentration dependence of the apparent molar volume and heat capacity resembled what is observed for strongly hydrophilic nonelectrolytes. These observations suggest that the effect of (small amounts of) DMSO on connectivity and fluctuations of the three-dimensional hydrogen-bonding system of water depends strongly on temperature. Above approximately -15-degrees-C DMSO promotes connectivity and introduces enhanced fluctuations of the H-bond network. At lower temperatures it inhibits fluctuations and possibly reduces connectivity of the water-water H-bonding system.