Glass transition dynamics and surface mobility of entangled polystyrene films at equilibrium

Zhaohui Yang, Andrew Clough, Chi Hang Lam, Ophelia K.C. Tsui

Research output: Journal article publicationJournal articleAcademic researchpeer-review

55 Citations (Scopus)


There has been continuing effort to understand the cause for the thickness dependence observed in the glass transition dynamics of polymer films. In a previous experiment, we showed that a two-layer model, assuming the films to contain a high-mobility surface layer residing on top of a bulklike inner layer, can explain the thickness dependence found in the viscosity of unentangled polystyrene films. Here, we examine the validity of this model in polystyrene films that are entangled. Unlike the unentangled films, the entangled ones are initially out-of-equilibrium, exhibiting a plateau modulus ∼1/10 times the bulk value. Upon annealing, the viscosity typically grows with time and eventually saturates. For the films with thickness above 20 nm, the saturated viscosity is the same as the bulk and takes ∼5-10 reptation times to reach. We find that the saturated viscosity is fully explainable by the two-layer model. A straightforward interpretation would imply that the surface mobile layer exists at equilibrium and modifies the dynamics of unentangled and entangled polymer films in a similar way.
Original languageEnglish
Pages (from-to)8294-8300
Number of pages7
Issue number20
Publication statusPublished - 25 Oct 2011

ASJC Scopus subject areas

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


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