Fig. 3
Fabrication steps for tribocharge-enabled EHDL of photopolymer. a Liquid-phase PDMS is poured onto the PC mold textured with a 2D triangular nanocone array. After thermal curing, the PDMS replica, textured with a nanocup array, is peeled off. Its surface becomes selectively tribocharged during this demolding process. b A UV-curable photopolymer (NOA73) is spin-coated on a silicon substrate and exposed to a UV-two-beam interference pattern. c The NOA73 thin film is textured sinusoidally with well-defined crest (C) and trough (T) areas due to local volume shrinkage. d The tribocharged PDMS nanocup array is placed on the sinusoidally textured NOA73 film. e NOA73 in the trough region is attracted upward by the spatially modulated electric fields originated from the tribocharges and undergoes EHDL. NOA73 on the crest experiences forces from both the capillary action and Coulomb attraction. f The cross-sectional profile defines the heights of the nanostructures in the crest (hc) and trough (ht) areas along with d, the nanocup depth. g The final UV-induced solidification of NOA73 and removal of the PDMS nanocup array completes the tribocharge-enabled EHDL of NOA73
