Nanoimprinting of Flexible Polycarbonate Sheets with a Flexible Polymer Mold and Application to Superhydrophobic Surfaces

This study demonstrates a reliable process for the direct nanoimprinting of a flexible polycarbonate (PC) sheet using a perfluoropolyether (PFPE) mold. PC is a commonly used flexible substrate with optical transparency, low thermal expansion coefficient, high mechanical strength, and excellent deformation resistivity. The imprint performances of PFPE, hard/soft-polydimethylsiloxane, and silicon molds are compared. Given that the heating temperature is near the glass transition temperature (approximate to 153 degrees C) of PC, only PFPE mold can be fully patterned into PC substrate with viable integrity. The mechanical property and gas permeability of the materials are investigated to determine the mechanism of the flexible PFPE mold, which performs better than a rigid silicon mold. Nanoimprint process using a PFPE mold is performed at 153 degrees C and 5 bars. The lower imprint temperature or imprint pressure of the proposed process compared with those from previous studies is favorable in nanoimprinting. Finally, nanoroughness-on-nanopillar hierarchical surfaces, which possess superhydrophobic slippery characteristics superior to those of nanoroughness-only surfaces, are obtained by treating PC nanopillar arrays imprinted by PFPE mold with C4F8 plasma.