Hypothesis: The micellization behavior of nonionic surfactants is significantly influenced by substituting ethylene oxide (EO) units with CO2 in the head group of nonionic C12EOj surfactants. Incorporating hydrophobic units has a major effect on the driving forces of the micellization process by a reduced hydration affinity. Hence, the incorporation of CO2 moieties is favoring micellization and thereby adding a further tuning parameter. Experiments: The micellization of the surfactants was characterized in terms of thermodynamics and the assembly properties on the water/air interface by isothermal titration calorimetry (ITC) and surface tension measurements. The incorporation of CO2 moieties was compared to the effect of propylene oxide (PO) and propiolactone (PL) over the temperature range of 25-50 degrees C. From ITC measurements and the van't Hoff relation, we determined the thermodynamic parameters of micellization: enthalpy (Delta H-mic), entropy (Delta S-mic), and Gibbs free energy (Delta G(mic)). Findings: The incorporation of CO2 moieties reduces the critical micellization concentration (cmc) and a transfer energy of -0.36 kT/CO2 unit quantifies favored micellization for CO2 surfactants. The presence of PO or CO2 in the head group has a similar effect on the cmc, but for CO2 Delta H-mic is substantially decreased, resulting in a largely reduced temperature sensitivity of the micellization process and indicating a reduced hydration affinity. This thermodynamic analysis reveals that CO2 and PO behave very differently concerning their effect on the micellization process. (C) 2020 Elsevier Inc. All rights reserved.