Interfacial Strengthening with Random Copolymers

  • S. T. Milner
  • G. H. Fredrickson


Recent experiments show increased interfacial strength of interfaces between immiscible A and B homopolymers when A/B random copolymers (RCs) are added at the interface. These results have been interpreted in terms of the work of Garel et al., which predicts that RCs at such A-B interfaces will adopt conformations in which long loops (of order 1/χ2 monomers) slightly rich in A (B) monomers will be found on the A (B) side of the interface. We reexamine these results in light of a simple Flory-Huggins description, which shows that such RCs would be immiscible with either A or B homopolymer with an effective χ parameter χ eff=χ/4 for symmetric RCs, and would tend to collapse at the A-B interface. Thus, the RC-homopolymer interface would then be only as strong as an interface between homopolymers with χ=χeff, which would be strong only if the A-B interface is nearly broad enough to be self-entangled already. Alternatively, if the RCs have a broad composition distribution, they can segregate by composition in strata, producing a “graded” interface. We derive criteria for the RC composition distribution and layer thickness in order that the resulting interface be strong.


Tube Diameter Random Copolymer Interfacial Strength Composition Distribution Interfacial Width 
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Copyright information

© Springer Science+Business Media New York 1997

Authors and Affiliations

  • S. T. Milner
    • 1
  • G. H. Fredrickson
    • 2
  1. 1.Exxon Research and EngineeringAnnandaleUSA
  2. 2.Dept. of Chemical EngineeringUniv. of CaliforniaSanta BarbaraUSA

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