Comparison of sodium dodecylsulfate apparent molar volumes and micellar aggregation numbers

The apparent molar volume of sodium dodecylsulfate (SDS) was determined vs. surfactant concentration in normal and 99.85 % heavy water solutions at 25 °C up to 0.8 mol/dm3. The apparent molar volume data in normal water were found to be systematically greater than those in heavy water. The apparent volume of aggregated SDS molecules v was found to be constant; in normal water for SDS concentrations greater than 0.04 mol/dm3, v=(4.1472 ± 0.0049) · 10−22 cm3, indicating no change in the intermolecular forces inside SDS micelles of increasing size.