Micellization and Physicochemical Properties of CTAB in Aqueous Solution: Interfacial Properties, Energetics, and Aggregation Number at 290 to 323 K

This work reports a detailed investigation of the micellization of the cationic surfactant cetyltrimethylammonium bromide (CTAB) over the temperature range of 290–313 K. Conductometry, tensiometry, fluorimetry, and isothermal titration calorimetry (ITC) were used to study the overall solution behavior of amphiphilic self-aggregation. The CMC values showed a trend of first declining and then rising with a minimum temperature of 298 K. The adsorption at the air–water interface and micellization processes of CTAB are both spontaneous. The enthalpy of CTAB micellization is negative at 290 K and increases negatively as the temperature rises. The interfacial parameters—maximum surface excess concentration (Γmax), minimum area per molecule (Amin), standard free energy of adsorption (Amin), and surface pressure at CMC (ΠCMC)—were calculated using surface tension data. The aggregation numbers (N) of CTAB micelles and others (SDS and CHAPS) determined at different [surfactant]>CMC by the static fluorescence quenching method were used to find out the N values at CMC (or NCMC). The results revealed that the NCMC values were 48, 54, and 4 for CTAB, SDS, and CHAPS micelles, respectively. Temperature-dependent NCMC by the ITC method was also examined for the studied surfactants. Additionally, the ITC-determined specific heat of micellization was used to find out the extent of water penetration into the micelle interior of up to 8, 7, and 3 hydrocarbons for CTAB, SDS, and CHAPS, respectively.