Three fundamental mechanical properties of supported glassy polystyrene films with thickness ranging from 250 nm to 9 nm were quantitatively determined by a recently developed wrinklingcracking method. Films below about 40 nm showed a decrease in both elastic modulus and fracture strength with decreasing film thickness, whereas the onset fracture strain was shown to increase. The observed variations in mechanical properties with respect to the bulk counterparts support the notion that a mechanically soft thin layer having a loosely-entangled chain network exists in the near-surface region of polymeric materials, whose contribution becomes more pronounced in thinner films.
Citation: ACS Macro Letters
Pub Type: Journals
wrinkling, cracking, polymers, thin films, mechanical properties, modulus, fracture, toughness