Neutron scattering characterization of homopolymers and graft-copolymer micelles in supercritical carbon dioxide

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Supercritical fluids are becoming an attractive alternative to the liquid solvents traditionally used as polymerization media. As the synthesis proceeds, a wide range of colloidal aggregates form, but there has hitherto been no way to measure such structures directly. We have applied small-angle neutron scattering (SANS) to characterize such systems, and although SCF polymerizations are carried out at high pressures, the penetrating power of the neutron beam means that typical cell windows are virtually transparent. Systems studied include molecules soluble in CO{sub 2} (e.g. polyfluoro-octyl acrylate or PFOA) and this polymer has previously been shown to exhibit a positive second ... continued below

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12 p.

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Chillura-Martino, D.; Triolo, R. & McClain, J. B. December 1995.

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Supercritical fluids are becoming an attractive alternative to the liquid solvents traditionally used as polymerization media. As the synthesis proceeds, a wide range of colloidal aggregates form, but there has hitherto been no way to measure such structures directly. We have applied small-angle neutron scattering (SANS) to characterize such systems, and although SCF polymerizations are carried out at high pressures, the penetrating power of the neutron beam means that typical cell windows are virtually transparent. Systems studied include molecules soluble in CO{sub 2} (e.g. polyfluoro-octyl acrylate or PFOA) and this polymer has previously been shown to exhibit a positive second virial coefficient (A{sub 2}). Other CO{sub 2}-soluble polymers include hexafluoro-polypropylene oxide (HFPPO), which appears to have a second virial coefficient which is close to zero (10{sup 4}A{sub 2} {approx_equal} 0 +{+-} 0.2 cm{sup 3} g{sup -2} mol). Polydimethylsiloxane (PDMS), is soluble on the molecular level only in the limit of dilute solution and seems to form aggregates as the concentration increases (c > 0.01 g cm{sup -3}). Other polymers (e.g. polystyrene) are insoluble in CO{sub 2}, though polymerizations may be accomplished via the use of PS-PFOA blockcopolymer stabilizers, which are also amenable to SANS characterization, and have been shown to form micelles in CO{sub 2}. Other amphiphilic surfactant molecules that form micelles include PFOA-polyethylene oxide (PFOA-PEO) graft copolymers, which swell as the CO{sub 2} medium is saturated with water. These systems have been characterized by SANS, by taking advantage of the different contrast options afforded by substituting D{sub 2}O for H{sub 2}O. This paper illustrates the utility of SANS to measure molecular dimensions, thermodynamic variables, molecular weights, micelle structures etc. in supercritical CO{sub 2}.

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12 p.

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OSTI as DE96005727

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  • Horizons in small-angle scattering from mesosopic systems, Stromboli (Italy), 27-30 Sep 1995

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  • Other: DE96005727
  • Report No.: CONF-9509328--1
  • Grant Number: AC05-84OR21400
  • Office of Scientific & Technical Information Report Number: 203969
  • Archival Resource Key: ark:/67531/metadc664672

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  • December 1995

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  • June 29, 2015, 9:42 p.m.

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  • Jan. 19, 2016, 8:27 p.m.

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Chillura-Martino, D.; Triolo, R. & McClain, J. B. Neutron scattering characterization of homopolymers and graft-copolymer micelles in supercritical carbon dioxide, article, December 1995; Tennessee. (digital.library.unt.edu/ark:/67531/metadc664672/: accessed December 11, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.