PHASE-BEHAVIOR OF FLUOROETHER-FUNCTIONAL AMPHIPHILES IN SUPERCRITICALCARBON-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 of fers a means to overcome low solubility of hydrophilic compounds in ca rbon dioxide, yet commercially-available ionic surfactants exhibit rel atively poor solubility in CO2 at moderate pressures. Synthesis of amp hiphiles containing functional groups which are known to interact favo rably, in a thermodynamic sense, with carbon dioxide offers a potentia l solution to this problem. Our results with fluoroether-functional am phiphiles show this to be a valid premise. Apparently, there are sever al competing effects that determine the solubility of these materials in carbon dioxide: increasing molecular weight tends to drive the clou d-point curve to higher pressures, yet, addition of CO2-philic fluoroe ther groups and branching of the CO2-philic tails works to depress the cloud-point curve to lower pressures. Further, increasing the polarit y of the polar head group induces the cloud-point curve to move to hig her pressures. Finally, we have shown that fluoroether-functional amph iphiles permit extraction of thymol blue from aqueous solution into ca rbon dioxide.