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Ultra small angle neutron scattering instruments have recently covered the gap between the size resolution available with conventional intermediate angle neutron scattering and small angle neutron scattering instruments on one side and optical microscopy on the other side. Rocks showing fractal behavior in over two decades of momentum transfer and seven orders of magnitude of intensity are examined and fractal parameters are extracted from the combined USANS and SANS curves. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper we report a SANS investigation of micelle formation by fluorocarbon-hydrocarbon block copolymers in supercritical CO[sub 2](scCO[sub 2]) at 313K. A sharp unimer-micelle transition is obtained due to the tuning of the solvating ability of scCO[sub 2] by profiling pressure. At high pressure the copolymer is in a monomeric state with a random coil structure. By lowering the pressure aggregates are formed with the hydrocarbon segments forming the core and the fluorocarbon segments forming the corona of spherical aggregates. This aggregate-unimer transition is driven by the gradual penetration of CO[sub 2] molecules toward the core of the aggregate and is critically related to the density of the solvent, thus suggesting the definition of a critical micellization density (CMD). © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]