English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

A simple and predictive model is put forward explaining the experimentallyobserved substantial shift of the glass transition temperature, Tg, ofsufficiently thin polymer films. It focuses on the limit of small molecularweight, where geometrical `finite size' effects on the chain conformation canbe ruled out. The model is based on the idea that the polymer freezes due tomemory effects in the viscoelastic eigenmodes of the film, which are affectedby the proximity of the boundaries. The elastic modulus of the polymer at theglass transition turns out to be the only fitting parameter. Quantitativeagreement is obtained with our experimental results on short chain polystyrene(Mw = 2 kg/mol), as well as with earlier results obtained with largermolecules. Furthermore, the model naturally accounts for the weak dependence ofthe shift of Tg upon the molecular weight. It furthermore explains whysupported films must be thinner than free standing ones to yield the sameshift, and why the latter depends upon the chemical properties of thesubstrate. Generalizations for arbitrary experimental geometries arestraightforward.Comment: 7 pages, 4 figure

The glass transition of thin polymer films: some questions, and a possible answer