Adiabatic compressibility of surfactant micelles in aqueous solution

The compressibilities of micellar solutions of the surfactants sodium dodecyl sulphate (SDS), sodium decyl sulphate (SDeS), sodium octyl sulphate (SOS), sodium decyl sulphonate (SDeSon), decyltrimethylammonium bromide (DeTABr), decylammonium bromide (DeABr) and dodecyltrimethylammonium bromide (DTABr) have been determined from sound-velocity measurements. A theoretical treatment has been introduced which enables the micellar compressibility (Kmic) to be evaluated from these data. From a systematic study of the above compounds it was found that a significant factor which controls the overall compressibility of the micellar aggregate is the nature of the surfactant head group. The overall picture is that the micelle resembles an aggregate with a compressible core surrounded by a less compressible surface structure.