ISSN:
0887-6266
Keywords:
polyethylene
;
polyolefins
;
blends
;
thermodynamics
;
neutron scattering
;
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Small-angle neutron scattering (SANS) measurements of interactions in polymer blends, χNS, generally depend on blend concentration Φ, even though χNS is evaluated with a model that assumes that the thermodynamic interaction parameter χFH = χNS is independent of Φ. Londono et al. have reported χNS to increase by ∼ 4× when Φ drops below 0.05 in polyethylene isotope blends. The relation between scattering and thermodynamics is addressed with incompressible Flory-Huggins theory wherein the nthermodynamic interaction parameter χ may vary with concentration Φ and degree of polymerization N; here χNS(Φ) ≠ χ(Φ). For polyethylene isotope and similar polyolefin blends, the strong upward curvature of χNS implies a modest (ca. 30%) increase of χ. Macroscopic phase behavior is unaffected because the shape of the binodal remains essentially unchanged. The Φ-dependence of χNS in turn depends on N, leading to the following empirical expression for the thermodynamic interaction parameter: χ(Φ, N) = β - (2γ′/NΦ1Φ2)(Φ1 ln Φ1 + Φ2 ln Φ2). For polyethylene isotope blends at 155°C, β = 2.85 × 10-4 and γ′ = 0.15. Simple Flory-Huggins behavior with χFH = β is recovered when N approaches infinity. The source of the Φ- and N-dependent second term is not known. © 1997 John Wiley & Sons, Inc. J Polym Phys 35: 2889-2899, 1997
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
