Security & Privacy
Webmaster
Review date: July 24, 2003
PNNL-SA-27883

Aggregation of Amphiphilic Molecules in Supercritical Carbon Dioxide: A Small Angle X-Ray Scattering Study

JL Fulton, DM Pfund, JB Mcclain, TJ Romack, EE Maury, JR Combes, ET Samulski, JM DeSimone, and M Capel. Langmuir 11, 4241-4249 (1995).

Abstract: Highly soluble amphiphilic materials are shown to form aggregates in supercritical CO2. The strategy for synthesis of these amphiphilic molecules involves incorporating CO2-philic segments that, for this study, are perfluorinated alkyl chains. These CO2-philic regions function like the hydrocarbon tails of conventional surfactant molecules used in liquid organic solvents. Synthesis and characterization of three different CO2 amphiphiles are reported. Subsequent small angle x-ray scattering (SAXS) measurements were used to characterize the aggregation of these materials in supercritical CO2. Each of the three amphiphiles studies showed a different type of aggregation behavior. A graft copolymer consisting of a CO2-philic backbone and CO2-phobic grafts associated into a micellar structure in the presence of water to promote hydrogen bonding. These aggregates contain approximately 600 grafts in the core. The commercially available surfactant, perfluoroalkyl-polyethylene oxide or F(CF2)610CH2CH2O(CH2CH2O)28H, forms classic reverse micelle structures having radii of about 84Å under the conditions of high pressure required to solubilize the material. A third amphiphile, the semifluorinated alkane diblock molecule F(CF2)10(CH2)10H, may form small aggregates of at most 4 unimers per aggregate. The improved understanding of amphiphile aggregation in CO2 will aid in the development of new routes for polymer and organic synthesis in this relatively benign solvent.