Abstract
The phase behavior of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymers (PEO-PPO-PEO Pluronics) in liquid and supercritical carbon dioxide has been studied by cloud point measurements. It shows that such trade hydrocarbonated surfactants are fairly soluble (0.1 wt.%) in carbon dioxide in relatively mild conditions of temperature and pressure (T < 65 °C, P < 30 MPa). An empirical model based on the molecular weight of the copolymer has been proposed to predict the pressure–temperature phase diagram for a series of Pluronics (10 wt.% of ethylene oxide). Furthermore, the water/CO2 interfacial tension has been measured to investigate the interactions between water and the polar moieties of the surfactants (PEO blocks and hydroxyl end-groups) as well as the interactions between CO2 and the “CO2-philic” moiety of the surfactants (PPO block). An interfacial saturation concentration was evidenced and it was shown to depend on the temperature at a given pressure. The cloud point curves and interfacial tension data are fully consistent with a change in the affinity of the surfactant for CO2 versus pressure and temperature. A correlation between CO2-philic characteristics and surface active properties of the copolymers is given.