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Nanoimprint lithography (NIL) is a micro/nanoscale patterning technology on thermoplastic polymer films, and has been widely used to fabricate functional micro/nanoscale patterns. NIL was also used to develop micro/nanoscale patterns on curved surfaces by employing flexible polymer stamps or micropatterned metal molds with macroscopic curvatures. In this study, two-step ultrasonic forming was used to develop micropatterns on a curved surface out of a flat metal stamp, by connecting ultrasonic imprinting and stretching processes. Ultrasonic imprinting was used to replicate functional micropatterns on a flat polymer film, using a flat ultrasonic horn and micropatterned metal stamps with prism and dot micropatterns. An ultrasonic stretching process was then used to form a curvature on the patterned film using a curved ultrasonic horn and a soft mold insert, to avoid damage to the pre-developed micropatterns. The ultrasonic horn was designed to have three different tip radii, and the resulting forming depth and curvature formation were investigated experimentally. As a result, three different curved surfaces containing two different micropatterns were obtained. The developed curved films containing micropatterns were then evaluated optically, and showed different optical diffusion and illumination characteristics according to the film curvature and micropattern type. These results indicate that the proposed technology can extend the functionality of conventional micropatterned products by imposing appropriate curvatures.

Surface wettability is the ability of a liquid to maintain contact with a solid surface, and there have been many studies aimed at controlling surface wettability for development of functional surfaces. In this study, an approach to control surface wettability is proposed by differentiating surface energy of polycarbonate in specified regions, using a combination of two surface treatments: (i) micropattern replication using selective ultrasonic imprinting and (ii) hydrophobic coating using organic silane. In both treatments, profiled masks were used to reduce surface energy in target regions where semi-hydrophobic polycarbonate surfaces were changed to hydrophobic states. Various combinations of selective ultrasonic imprinting and hydrophobic coating were investigated in terms of changes in surface wettability, by measuring contact angle (CA) behaviors on the developed surfaces. By controlling such changes, the surface wettability of regions on a single polycarbonate surface could be differentiated, allowing semi-hydrophobic (CA 87.8°), hydrophobic (CA 114.8°) and superhydrophobic (CA 155.6°) states to coexist. This high CA difference (>60°) on a single surface was then applied to enhance water-repellent characteristics so that the surface wettability could be controlled effectively. Mechanical durability of the developed hybrid surface was also discussed by investigating its CA behavior after surface abrasion. [ABSTRACT FROM AUTHOR]

Recent advances in micro/nano technology have driven artificial modifications of surface wettability by mimicking biological surfaces, such as superhydrophobic and water-harvesting surfaces. In this study, surface wettability of polycarbonate (PC) films was modified using various surface treatments: micropatterning using ultrasonic imprint lithography, fluorinate silane coating, and electron beam irradiation. To modify surface wettability selectively in a specified region, these three treatments were performed using profiled masks with the corresponding shapes. Various combinations of these treatments were investigated in terms of wettability changes, by measuring contact angle (CA). The semi-hydrophobic PC film (CA: 89.2°) was modified to create a superhydrophobic state (CA: 155.9°) by virtue of the selective micropatterning and coating. The electron beam irradiation had an opposite effect, reducing the CA (48.2°), so that the irradiated region was modified to create a hydrophilic state. Two combinations of the proposed surface modifications made it possible to have a great difference in CA on a single surface (107.7°), and to have four different wetting states on a single surface. Various water-drop experiments proved that the developed hybrid surfaces were selectively wettable and showed water-collecting capability. [ABSTRACT FROM AUTHOR]

Ultrasonic imprinting is a patterning technology in which ultrasonic vibration energy is used to soften the surface of thermoplastic polymer to allow the formation of micropatterns. Compared with other patterning technologies, ultrasonic imprinting has the advantages of short cycle time and low energy consumption. This study deals with the selective ultrasonic imprinting process, which provides higher flexibility in developing versatile micropatterns. Selective ultrasonic imprinting uses a profiled mask film by which ultrasonic waves are transferred from an ultrasonic horn to a target polymer film. The target polymer film is locally softened in the regions in contact with the mask film, so that micropatterns can be selectively replicated in these regions. In this study, this localized heating mechanism is numerically investigated through structural-thermal-coupled finite element analysis, by effectively connecting transient structural and heat transfer analyses. This coupled simulation was performed to investigate the localized heating mechanism of the selective imprinting using an E-shaped mask, and then compared with experimental findings. Micropattern replication was then performed using an arbitrarily shaped logo, with which differentiation of optical transparency could be obtained. [ABSTRACT FROM AUTHOR]

Highlights: [•] Selective ultrasonic imprinting is developed to replicate micropatterns on predefined areas. [•] A profiled mask film is inserted between a target film and an ultrasonic horn. [•] Ultrasonic waves are selectively transferred to the target film through the mask film. [•] Temperature increase and material softening are concentrated in the masked region. [•] Selective imprinting can be applied to micropattern replications on arbitrarily profiled areas. [Copyright &y& Elsevier]

Nanoimprint lithography (NIL) is a micro/nanoscale patterning technology on thermoplastic polymer films, and has been widely used to fabricate functional micro/nanoscale patterns. NIL was also used to develop micro/nanoscale patterns on curved surfaces by employing flexible polymer stamps or micropatterned metal molds with macroscopic curvatures. In this study, two-step ultrasonic forming was used to develop micropatterns on a curved surface out of a flat metal stamp, by connecting ultrasonic imprinting and stretching processes. Ultrasonic imprinting was used to replicate functional micropatterns on a flat polymer film, using a flat ultrasonic horn and micropatterned metal stamps with prism and dot micropatterns. An ultrasonic stretching process was then used to form a curvature on the patterned film using a curved ultrasonic horn and a soft mold insert, to avoid damage to the pre-developed micropatterns. The ultrasonic horn was designed to have three different tip radii, and the resulting forming depth and curvature formation were investigated experimentally. As a result, three different curved surfaces containing two different micropatterns were obtained. The developed curved films containing micropatterns were then evaluated optically, and showed different optical diffusion and illumination characteristics according to the film curvature and micropattern type. These results indicate that the proposed technology can extend the functionality of conventional micropatterned products by imposing appropriate curvatures. [ABSTRACT FROM AUTHOR]

Recent advances in micro/nano technology have driven artificial modifications of surface wettability by mimicking biological surfaces, such as superhydrophobic and water-harvesting surfaces. In this study, surface wettability of polycarbonate (PC) films was modified using various surface treatments: micropatterning using ultrasonic imprint lithography, fluorinate silane coating, and electron beam irradiation. To modify surface wettability selectively in a specified region, these three treatments were performed using profiled masks with the corresponding shapes. Various combinations of these treatments were investigated in terms of wettability changes, by measuring contact angle (CA). The semi-hydrophobic PC film (CA: 89.2°) was modified to create a super- hydrophobic state (CA: 155.9°) by virtue of the selective micropatterning and coating. The electron beam irradiation had an opposite effect, reducing the CA (48.2°), so that the irradiated region was modified to create a hydrophilic state. Two combinations of the proposed surface modifications made it possible to have a great difference in CA on a single surface (107.7°), and to have four different wetting states on a single surface. Various water-drop experiments proved that the developed hybrid surfaces were selectively wettable and showed water-collecting capability.