Slippery or Sticky Boundary Conditions: Control of Wrinkling in Metal-Capped Thin Polymer Films by Selective Adhesion to Substrates

Wrinkling patterns at the metallized surface of thin polymer films are shown to be sensitive to the sticky or slippery character of the polymer-substrate interface. Existing theoretical models were expanded to specific boundary conditions (adhesive versus slippery) in order to rationalize these observations. Based on this concept, we were able to propose a new and simple method to orient the wrinkles by chemically patterning the substrate with regions of high and low adhesion.

Figure 1

Optical Micrographs of wrinkled surfaces obtained with a 20 nm thick metal layer and a 60 nm polymer layer on chemically patterned gold substrates, after annealing at $130°\mathrm{C}$. Alternating stripe widths are (a) $5\mu \mathrm{m}/5\mu \mathrm{m}$, (b) $10\mu \mathrm{m}/10\mu \mathrm{m}$.

Figure 2

Schematic representation of wrinkle formation on a bare substrate. (a) Layered system prior to heating. (b) Upon heating, (left) expansion that would be obtained for each layer independently in the absence of any surrounding material and (right) distribution of the compressive stresses in the trilayer prior to wrinkling. (c) Deformation profile in the polymer layer induced by wrinkling in adhesive (left) and slippery regions (right).

Figure 3

Evolution of the wavelength versus the product of the metal and polymer thickness for trilayers $\mathrm{Ti}/\mathrm{PS}/\mathrm{Si}$ heated at $130°\mathrm{C}$. The inset shows OM image of a wrinkled surface obtained with a 15 nm thick metal layer and a 350 nm thick polymer layer [the Fast Fourier Transform (FFT) of a broad sample area, 10 times larger than the OM image is also shown].

Figure 4

Schematic representation of the slight membrane displacement (and corresponding deformation of the polymer layer) when wrinkles appear above slippery regions. This displacement induces the observed preferred wrinkle orientation above slippery stripes (and later the observed opposite preferred orientation above sticky stripes). It is also at the origin of the contrasted wrinkle amplitude between both types of regions.