The third-normal stress difference in entangled melts: Quantitative stress-optical measurements in oscillatory shear

R. M. Kannan, J. A. Kornfield

Research output: Contribution to journalArticle

Abstract

Stress-optical measurements are used to quantitatively determine the third-normal stress difference (N3 = N1 + N2) in three entangled polymer melts during small amplitude (<15%) oscillatory shear over a wide dynamic range. The results are presented in terms of the three material functions that describe N3 in oscillatory shear: the real and imaginary parts of its complex amplitude ψ3*= ψ3- iψ3, and its displacement ψ3d. The results confirm that these functions are related to the dynamic modulus by ω2ψ3*(ω)=(1-β)[G*(ω))- {Mathematical expression}G*(2ω)] and ω2ψ3d(ω)=(1- β)G′(ω) as predicted by many constitutive equations, where β = -N2/N1. The value of (1-β) is found to be 0.69±0.07 for poly(ethylene-propylene) and 0.76±0.07 for polyisoprene. This corresponds to -N2/N1 = 0.31 and 0.24±0.07, close to the prediction of the reptation model when the independent alignment approximation is used, i.e., -N2/N1 = 2/7 - 0.28.

Original languageEnglish (US)
Pages (from-to)535-544
Number of pages10
JournalRheologica Acta
Volume31
Issue number6
DOIs
StatePublished - Nov 1 1992
Externally publishedYes

Keywords

  • entangled melts
  • flow birefringence
  • oscillatory shear
  • poly(ethylene-propylene)
  • polyisoprene
  • third normal stress difference

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics

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