The Effect of the Pressure on the Micellization of the Surfactant in Aqueous Urea Solutions

Abstract

The critical micelle concentrations (CMC) of dodecyltrimethylammonium bromide (DTAB) in aqueous urea solutions have been determined over a range of pressures up to 2500 atm at 25 and 35 °C. The partial molal volumes of DTAB in micellar (\barVm) and singly-dispersed states (\barVs) have also been determined in aqueous urea solutions at 25 °C. \barVs increases with the addition of urea, while \barVm remains approximately constant. The partial molal entropy change of micellization (Δ\barSm) in water increases with an increase in the pressure up to about 1500 atm, while Δ\barSm in 3-m urea solution remains virtually unaltered in the low-pressure region. The results suggest that the “iceberg” structure of water around the hydrocarbon chain of the monomeric surfactant is effectively broken down by urea.