Local and Global Stretching of Polymer Chains during Startup of Extensional Flow

Carlos R. López-Barrón*, Wesley R. Burghardt, Mu Sung Kweon

*Corresponding author for this work

Research output: Contribution to journalArticle

1 Scopus citations

Abstract

The nonlinear rheological response to extensional flows in entangled polymers is related to the segmental chain stretching and to the chemical identity of the monomeric units. The latter has a strong effect on the drag coefficients, and therefore, quantification of molecular conformation changes in the subnanometer scale (at the monomer level) are crucial to fully understand nonlinear viscoelastic behavior in polymer melts. We report in situ time-resolved extensional rheo-small-angle neutron scattering (tEr-SANS) and wide-angle X-ray scattering (tEr-WAXS) during startup of uniaxial flow on a monodisperse polystyrene melt. Flow-induced segmental alignment was quantified with tEr-SANS, whereas local alignment of the backbone-backbone and phenyl-phenyl interactions were measured with tEr-WAXS. Linear relations between the three alignment factors and stress were observed at low stresses, which confirmed the validity of simple stress-SANS and stress-WAXS rules (SSR and SWR, respectively). Significant differences in SSR and SWR coefficients, as well as the stress values for failure of the two rules suggest very different correlations between global (at the segmental level) and local (at the monomer level) conformations with stress.

Original languageEnglish (US)
Pages (from-to)26-31
Number of pages6
JournalACS Macro Letters
Volume9
Issue number1
DOIs
StatePublished - Jan 21 2020

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ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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