Thermodynamics of Micellization of Some Nonionic Surfactants in Water

The enthalpies of solution (̅H₂-H⁰₂) of some nonionic surfactants polyoxyethylene alkyl ethers (C₁₀E₄C₁₀E₅, C₁₀E₆, C₁₀E₈, C₁₂E₈) and Triton X-100, in water have been measured calorimetrically in pre-CMC and post-CMC regions in the temperature range 283.15 to 328.15 K. From the enthalpies of solution data have been derived the enthalpy of micellization, ΔH_m, the heat capacities of monomeric ΔC_Pmono and micellar forms ΔC_Pmic as well as the heat capacities of micellization ΔC_Pm. The effect of temperature and size of the polar head and non-polar groups of the surfactants has been discussed in terms of the contributions of hydrophobic, hydrophilic and hydrogen bonding interactions. The ΔC_Pm values indicate that there is an appreciable water penetration into the micellar core.