Abstract
Functional films with hydrophobic, oleophobic, anti-fouling, anti-icing, anti-bacterial and low reflectance properties can be produced by patterning nano- or micro-structures on films via nano imprint lithography. Here, an omni-phobic surface showing both hydrophobicity and oleophobicity was obtained without chemical surface treatment by increasing the surface roughness and deforming the pattern morphology using only nano imprint lithography and the oxygen-inhibited curing properties of polyurethane acrylate (PUA) resin. A tulip-shaped pattern imprinting process was designed in which microscale patterns were fabricated using a porous polydimethylsiloxane (PDMS) mold with high oxygen transmission. During ultraviolet (UV) curing, a curing inhibiting layer was formed by reaction with oxygen. Next, a PDMS pad was used for the pressurized curing of the curing inhibition layer to modify the micro scale structures. Finally, final curing of the deformed pattern was performed using ultra high-power UV light. The deformation of the pattern into tulip-like shapes with increased surface roughness was confirmed by microscopy, and contact angle measurement was performed to confirm omni-phobicity. The final cured imprinted samples showed water and oil contact angles reaching 169.2° and 115°, respectively; thus, the omni-phobic surface could be demonstrated by a tulip-shaped pattern imprinting process.
Highlights
Functional films that realize characteristics appearing in nano- and micro-scale patterns have been fabricated biomimetically [1–12]
Micro-sized structures were patterned on a substrate using ultraviolet (UV) nano-imprint lithography among soft lithography
Among the materials used in the UV nano-imprint lithography process, polyurethane acrylate (PUA) resins include radical polymerization resins containing acrylate as the main component and cation polymerization resins containing epoxy as the main component
Summary
Functional films that realize characteristics appearing in nano- and micro-scale patterns have been fabricated biomimetically [1–12]. Micro-sized structures were patterned on a substrate using ultraviolet (UV) nano-imprint lithography among soft lithography. Radical polymerization resins have a property of inhibiting UV curing by generating an inert material (I-R-O-O) when reacting with oxygen This characteristic deteriorates the mechanical properties of fine structures manufactured with the correct dimensions. When PUA was imprinted using a porous polydimethylsiloxane (PDMS) mold, oxygen inherent in the mold cavity or penetrating the mold diffused into the resin, inhibiting ultraviolet (UV) curing. This produced partially cured structures with Bingham plastic behaviors; the partially cured structures deformed under the application of pressure exceeding the yield stress [16]. When applying the Roll-to-Roll process, it is possible to fabricate a large-area omni-phobic surface
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