| We report the formation of highly oriented wrinkling on the surface of the bilayer (polystyrene (PS)/poly(vinyl pyrrolidone) (PVP)) confined by a polydimethylsiloxane (PDMS) mold in a water vapor environment. When PVP is subjected to water vapor, the polymer loses its mechanical rigidity and changes to a viscous state, which leads to a dramatic change in Young's modulus. This change generates the amount of strain in the bilayer to induce the wrinkling. With a shape-controlled mold, we can get the ordered wrinkles perfectly perpendicular or leaned 45°to the channel orientation of the mold because the orientation of the resultant force changes with the process of water diffusion which drives the surface to form the wrinkling. Additionally, we can get much smaller wrinkles than the stripe spacing of PDMS mold about one order. The wrinkle period changes with the power index of about 0.5 for various value of the multiplication product of the film thicknesses of the two layers, namelyλ～(hPShPVP)1/2.
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