Communications ADVANCED MATERIALSdesiccator under vacuum for 20 min to remove air bubbles trapped in the liquid prepolymer, When features on the surface of the shrunken film were deep, many small air bubbles could not escape but settled down at the interface between the liquid prepolymer and the solid shrunken film. The air bubbles were thus replicated into the replica after the prepolymer was solidified (e.g. the surface texture shown in Fig. 2b-d). We used a UV-curable polyurethane (NOA73, Norland Products, New Brunswick, NJ) and a heatcurable epoxy (F114, Tra-Con, Medford. MA) to replicate the surface of shrunken films. The prepolymcr of NOA73 was irradiated with a UV light (Type 7825-34, Canrdd-Hanovia 450 W medium-pressure Hg vapor lamp, Ace Glass, Tnc., Vineland. NJ) for 45 min, with samples placed at a distance of -1-2 cm from the lamp. The precursor of F114 was cross-linked at 65 "C for 4 h.

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