One-step fabrication of optically transparent polydimethylsiloxane artificial lotus leaf film using under-exposed under-baked photoresist mold

We report an extremely simple one-step fabrication method of flexible, optically transparent super-hydrophobic polydimethylsiloxane (PDMS) thin film using under-exposed under-baked photoresist (PR) mold. Significant under soft bake condition makes photoresist retains good amount of solvents which greatly increase the dissolution rate. Once this condition is combined with the under-exposure condition, it would create a mushroom-like structure on the PR mold. The replicated PDMS using this PR mold showed hierarchical micro/nano scale features on the high aspect ratio pillar array structure. Contact angles and optical transmittance of various surfaces were tested and results were compared. A static contact angle as high as 163° was achieved. These micro/nano patterned super-hydrophobic transparent PDMS films could be used in various water-repellent applications.