Organisms often have superior abilities. For example, the moth’s eyes block the reflection of light, preventing even the slightest light from escaping. Morpho butterflies have vivid colors despite their lack of pigmentation. The superhydrophobicity of lotus leaves is another example, which is attributed to their characteristic surface structure. We have recreated an interesting property by mimicking the structure of rose petals. When a drop of water falls on a rose petal, it adheres to the petal like a sphere. The droplets stay in place when the petals are inverted in this state. This phenomenon is called the rose petal effect. The surface of the petals is lined with microscale hemispherical structures, and each surface has additional nanoscale grooves. The effect is due to the hierarchical structure of nano- and microstructures. When water is dropped onto these structures, the surfaces of the nanostructures become air pockets, preventing water from entering the grooves. This results in stronger water repellency compared to that of the same material with a smooth surface. In contrast, when water penetrates the microstructure, the surface area becomes larger than that of a smooth surface, increasing adhesion. This is called the Wenzel mode. Here, we attempted to reproduce this structure on film using a combination of high-throughput techniques; ultraviolet nanoimprint lithography (UV-NIL) and roll pressing. The manufacturing process comprises two main steps. First, a nanopillar structure called a moth-eye structure is fabricated over the entire surface using UV-NIL. This serves the same purpose as the nanoglobe structure. Next, microscale holes are drilled on the surface using a roll press method. The resulting depressions immobilize water droplets and improve adhesion. Despite the strong water repellency obtained through this method, with a contact angle of more than 140±b°, up to 9 µL of water droplets remained attached to the film even when the film was turned over. Because this method can impart adhesion at any position on the water-repellent surface, it can be applied to microdroplet transport.

1. [1] J. F. V. Vincent, O. A. Bogatyreva, N. R. Bogatyrev, A. Bowyer, and A. K. Pahl, “Biomimetics: its practice and theory,” J. R. Soc. Interface, Vol.3, No.9, pp. 471-482, 2006. https://doi.org/10.1098/rsif.2006.0127
2. [2] M. E. Abdelsalam, P. N. Bartlett, T. Kelf, and J. Baumberg, “Wetting of Regularly Structured Gold Surfaces,” Langmuir, Vol.21, No.5, pp. 1663-2092, 2005. https://doi.org/10.1021/la047468q
3. [3] M. Yu, S. Chen, B. Zhang, D. Qiu, and S. Cui, “Why a lotus-like superhydrophobic surface is self-cleaning? An explanation from surface force measurments and analysis,” Langmuir, Vol.30, No.45, pp. 13615-13621, 2014. https://doi.org/10.1021/la5041272
4. [4] L. Wang, S. Zhang, S. Li, S. Yan, and S. Dong, “Inner surface of Nepenthes slippery zone: ratchet effect of lunate cells causes anisotropic superhydrophobicity,” R. Soc. Open Sci., Vol.7, No.3, 2020. https://doi.org/10.1098/rsos.200066
5. [5] A. R. Parker and C. R. Lawrence, “Water capture by a desert beetle,” Nature, Vol.414, pp. 33-34, 2001. https://doi.org/10.1038/35102108
6. [6] W. J. Hamilton III and M. K. Seely, “Fog basking by the Namib Desert beetle, Onymacris unguicularis,” Nature, Vol.262, pp. 284-285, 1976. https://doi.org/10.1038/262284a0
7. [7] L. Feng, Y. Zhang, J. Xi, Y. Zhu, N. Wang, F. Xia, and L. Jiang., “Petal Effect: A Superhydrophobic State with High Adhesive Force,” Langmuir, Vol.24, No.8, pp. 4114-4119, 2008. https://doi.org/10.1021/la703821h
8. [8] B. Bhushan and M. Nosonovsky, “The rose petal effect and the modes of superhydrophobicity,” Philos. Trans. R. Soc. A, Vol.368, No.1929, pp. 4713-4728, 2010. https://doi.org/10.1098/rsta.2010.0203
9. [9] L. Shang, Y. Cheng, and Y. Zhao, “Emerging Droplet Microfluidics,” Chem. Rev., Vol.117, No.12, pp. 7964-8040, 2017. https://doi.org/10.1021/acs.chemrev.6b00848
10. [10] M. Cao, J. Ju, K. Li, S. Dou, K. Liu, and L. Jiang, “Facile and large-scale fabrication of a cactus-inspired continuous fog collector,” Adv. Funct. Mater., Vol.24, No.21, pp. 3235-3240, 2014. https://doi.org/10.1002/adfm.201303661
11. [11] A. B. D. Cassie and S. Baxter, “Wettability of porous surfaces,” Trans. Faraday Soc., Vol.40, pp. 546-551, 1944. https://doi.org/10.1039/TF9444000546
12. [12] R. N. Wenzel, “Resistance of solid surfaces to wetting by water,” Ind. Eng. Chem., Vol.28, No.8, pp. 988-994, 1936. https://doi.org/10.1021/ie50320a024
13. [13] K. Fujiwara, H. Sugawara, and J. Taniguchi, “Fabrication of a rose-petal-inspired micro/nanostructured surface via the ultraviolet nanoimprint lithography and roll-press methods,” J. Photopolym. Sci. Technol., Vol.35, No.2, pp. 117-123, 2022. https://doi.org/10.2494/photopolymer.35.117
14. [14] Y. Kanemori, M. Okouchi, and K. Hane, “Fabrication of antireflective subwavelength-grating structures on optical fiber end faces using UV nanoimprinting technique,” Trans. Jpn. Soc. Mech. Eng. C, Vol.76, No.771, pp. 2854-2860, 2010 (in Japanese). https://doi.org/10.1299/kikaic.76.2854
15. [15] B. K. Mousavi, A. K. Mousavu, T. Busani, M. H. Zadeh, and S. R. J. Brueck, “Nanostructured anti-reflection coatings for enhancing transmission of light,” J. Appl. Math. Phys., Vol.7, No.12, 2019. https://doi.org/10.4236/jamp.2019.712217
16. [16] S. J. Park, S. W. Lee, K. J. Lee, J. H. Lee, K. D. Kim, J. H. Jeong, and J. H. Choi, “An antireflective nanostructure array fabricated by nanosilver colloidal lithography on a silicon substrate,” Nanoscale Res. Lett., Vol.5, pp. 1570-1577, 2010. https://doi.org/10.1007/s11671-010-9678-y
17. [17] C. H. Sun, P. Jiang, and B. Jiang, “Broadband moth-eye antireflection coatings on silicon,” Appl. Phys. Lett., Vol.92, No.6, 2008. https://doi.org/10.1063/1.2870080
18. [18] Y. Kanamori, K. Hane, H. Sai, and H. Yugami, “100-nm period silicon antireflection structures fabricated using a porous alumina membrane mask,” Appl. Phys. Lett., Vol.78, No.2, pp. 142-143, 2001. https://doi.org/10.1063/1.1339845
19. [19] T. Yanagishita, K. Yasui, T. Kondo, Y. Kawamoto, K. Nishio, and H. Masuda, “Antireflection polymer surface using anodic porous alumina molds with tapered holes,” Chem. Lett., Vol.36, No.4, pp. 530-531, 2007. https://doi.org/10.1246/cl.2007.530
20. [20] J. Taniguchi, Y. Kamiya, and N. Unno, “Fabrication of anti-refrection structure using photo-curable polymer,” J. Photopolym. Sci. Technol., Vol.24, No.1, pp. 105-110, 2011. https://doi.org/10.2494/photopolymer.24.105
21. [21] J. Taniguchi, Y. Nemoto, and Y. Sugiyama, “Fabrication of non reflective structure on glassy carbon surface using oxygen ion beam irradiation,” J. Nanosci. Nanotechnol., Vol.9, No.1, pp. 445-449, 2009. https://doi.org/10.1166/jnn.2009.J039
22. [22] R. Fukuyama, J. Taniguchi, K. Yoshikawa, and H. Yagishita, “Pierce characteristics of titanium foil with roll press method,” Microelectron. Eng., Vol.150, pp.74-83, 2016. https://doi.org/10.1016/j.mee.2015.11.009
23. [23] H. Eto, S. Hiwasa, and J. Taniguchi, “Tough and antifouling antireflection structures made by partial-filling ultraviolet nanoimprint lithography,” Microelectron. Eng., Vol.197, No.5, pp. 33-38, 2018. https://doi.org/10.1016/j.mee.2018.04.017