Anisotropy of Shear Relaxation in Confined Thin Films of Unentangled Polymer Melts

Brendan C. Abberton, Wing Kam Liu, Sinan Keten*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The anisotropic shear relaxation functions of confined thin films of unentangled polymer melts are measured via nonequilibrium step-strain simulations of in-plane and out-of-plane shear using the finitely extensible, nonlinear-elastic (FENE) model. We show that the classical Rouse model unsurprisingly fails to predict the thin-film relaxation functions in response to out-of-plane shear, due in part to non-Gaussian conformation statistics in the dimension perpendicular to the sub/superstrate. Using an alternate empirical model for the out-of-plane response, we quantify decreases in the plateau modulus G⊥P, relaxation time λ, and viscosity η and an increase in the logarithmic relaxation rate r as functions of film thickness, and we discuss these anisotropic changes in stress-relaxation properties in terms of structural/conformation changes on the microscopic level, namely the relative contraction and non-Gaussian quality of polymer conformations in the dimension normal to the substrate and the resulting phenomenon of cooperative relaxation. We then incorporate these into a semiempirical extension to the Rouse model which closely predicts our computational results and which will be useful for further study of polymer thin films.

Original languageEnglish (US)
Pages (from-to)7631-7639
Number of pages9
Issue number20
StatePublished - Oct 27 2015

ASJC Scopus subject areas

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


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