Density and Viscosity of Octyl, Decyl, and Dodecyl Sodium Sulfates in Ethanol

The density of mixtures of a homologous series of sodium alkyl sulfate (H(CH 2 ) n OSO 3 - Na + surfactants (where n = 8, 10, and 12) in ethanol has been measured as a function of concentration and temperature, and the apparent molal volumes have been derived. The calculated partial molal volume of sodium ion (V° Na+ ) at infinite dilution from the three surfactants is found equal to -14.23, -13.75, and -10.44 cm 3 . mol -1 at 25, 35, and 45 °C, respectively. The electrostriction of the alcohol molecules by the hydrophobic part H(CH 2 ) n OSO 3 - has been found to be almost negligible since the central charge is partially masked by the large hydrocarbon group. The Jones-Dole equation is used to determine the ionic β coefficient from viscosity measurements. The data are interpreted in light of structure-making or structure-breaking phenomena.