Surface Tension, Heat Capacity, and Volume of Amphiphilic Compounds in Formamide Solutions

Density measurements of sodium dodecyl sulfate (SDS), sodium decyl sulfate (SDeS), sodium octyl sulfate(SOS), and sodium hexyl sulfate(SHS) in formamide (FA) as functions of the surfactant concentrations were carried out at 25°C. For SDS in FA, additional density measurements at 35 and 60°C and surface tension and specific heat capacity measurements at 25°C were also performed. From density and specific heat capacity data, the apparent molar volume and heat capacity of the surfactants as functions of concentration were calculated. The surface excess of SDS at the solution–air interface was also determined from the surface tension measurements using the Gibbs adsorption equation. Under our experimental conditions, none of the experimental results evidence micelle formation. In addition, volumetric studies of the hexanol–SDS–FA ternary system at 25°C evidence only interactions between the dispersed surfactant and alcohol.