Structure of diblock copolymers in supercritical carbon dioxide and critical micellization pressure
- Department of Physical Chemistry, University of Palermo, Vialle delle Scienze, Parco d'Orleans II, 90128 Palermo, (Italy)
- School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, (United Kingdom)
- ISIS, Rutherford Appleton Laboratory, Chilton, Oxon OX11 OQX, (United Kingdom)
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599 (United States)
This paper reports a small angle neutron scattering investigation of micelle formation by fluorocarbon-hydrocarbon block copolymers in supercritical CO{sub 2}(sc-CO{sub 2}) at 65 degree sign C. A sharp unimer-micelle transition is obtained due to the tuning of the solvating ability of sc-CO{sub 2} by profiling pressure, so that the block copolymer, in a semidilute solution, finds sc-CO{sub 2} a good solvent at high pressure and a poor solvent at low pressure. At high pressure the copolymer is in a monomeric state with a random coil structure. However, on lowering the pressure, aggregates are formed with a structure similar to aqueous micelles with the hydrocarbon segments forming the core and the fluorocarbon segments forming the corona of the micelle. This unimer-aggregate transition is driven by the gradual elimination of CO{sub 2} molecules solvating the hydrocarbon segments of the polymer. Comparison of these results with related data on the same polymer at different temperatures indicates that the transition is critically related to the density of the solvent. This suggests the definition of a critical micellization density, to our knowledge a new concept in colloid chemistry. (c) 2000 The American Physical Society.
- OSTI ID:
- 20216100
- Journal Information:
- Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, Journal Name: Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics Journal Issue: 4 Vol. 61; ISSN PLEEE8; ISSN 1063-651X
- Country of Publication:
- United States
- Language:
- English
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