Wrenching of a metal thin film on a structured polymer layer

We report on the wrenching of a metal-capped periodically corrugated polymer bilayer when the bilayer is annealed at a temperature far above the glass transition temperature of the polymer layer. Certain corrugation geometries such as several micrometre line width of groove and ridge and step heights, thicknesses of the metal film, and extents of reduction of the elastic modulus of the polymer layer by increasing the annealing temperature give rise to a wrenching pattern in the metal surface. This wrenching pattern was characterized by the critical wrenching angle. The critical wrenching angle could be theoretically determined by calculating the mechanical energy required for the wrenching of the metal film and polymer layer in order to relax the thermal compressive in-plane stress. An increase in the annealing temperature incorporated with a decrease in the corrugation period yields a smaller critical wrenching angle. For the critical wrenching angle larger than a certain value, the wrenching wave pattern was directed by the wave interaction relationship between the corrugation and the intrinsic buckling wave of the metal-capped polymer bilayer.