PHASE-BEHAVIOR OF FLUOROETHER-FUNCTIONAL AMPHIPHILES IN SUPERCRITICAL CARBON-DIOXIDE

The observed low solubility of hydrophilic compounds in non-polar CO2 can limit applications of supercritical-fluid technology in some high growth industries, such as biotechnology. Reverse micelle formation offers a means to overcome low solubility of hydrophilic compounds in carbon dioxide, yet commercially-available ionic surfactants exhibit relatively poor solubility in CO2 at moderate pressures. Synthesis of amphiphiles containing functional groups which are known to interact favorably, in a thermodynamic sense, with carbon dioxide offers a potential solution to this problem. Our results with fluoroether-functional amphiphiles show this to be a valid premise. Apparently, there are several competing effects that determine the solubility of these materials in carbon dioxide: increasing molecular weight tends to drive the cloud-point curve to higher pressures, yet, addition of CO2-philic fluoroether groups and branching of the CO2-philic tails works to depress the cloud-point curve to lower pressures. Further, increasing the polarity of the polar head group induces the cloud-point curve to move to higher pressures. Finally, we have shown that fluoroether-functional amphiphiles permit extraction of thymol blue from aqueous solution into carbon dioxide.