Method Article

Multiscale Structures Aggregated by Imprinted Nanofibers for Functional Surfaces

DOI:

10.3791/58356

⸱

September 11th, 2018

 ,  ,  ,  ,  ,  ,  , 
1Department of Mechanical Engineering, Changwon National University, 2Department of Mechanical Engineering, Massachusetts Institute of Technology, 3Printed Electronics Research Team, Korea Institute of Machinery and Materials

* These authors contributed equally

In This Article

Summary

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Presented is an easy method to fabricate nano-micro multiscale structures, for functional surfaces, by aggregating nanofibers fabricated using an anodic aluminum oxide filter.

Abstract

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Multiscale surface structures have attracted increasing interest owing to several potential applications in surface devices. However, an existing challenge in the field is the fabrication of hybrid micro-nano structures using a facile, cost-effective, and high-throughput method. To overcome these challenges, this paper proposes a protocol to fabricate multiscale structures using only an imprint process with an anodic aluminum oxide (AAO) filter and an evaporative self-aggregation process of nanofibers. Unlike previous attempts that have aimed to straighten nanofibers, we demonstrate a unique fabrication method for multiscale aggregated nanofibers with high aspect ratios. Furthermore, the surface morphology and wettability of these structures on various liquids were investigated to facilitate their use in multifunctional surfaces.

Introduction

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Nanoscale textured structures such as nanoparticles, nanotubes, and nanofibers have attracted attention in the scientific community, as they demonstrate unique characteristics in various applications including electrical, biomedical, optical, and surface engineering1,2,3,4,5,6,7,8. In particular, nanofibers are widely used in stretchable and transparent electrodes9, wearable sensors10,11, interconnections12,13, and nano-optics applications14. Among the various methods of fabricating nanoscale structures, such as sol-gel methods, self-assembly, lithography, and replication15,16,17,18,19,20, direct replication using a template is currently considered a promising method because it is simple, cost-effective, and applicable to various curable materials21,22,23,24,25,26.

Owing to its multiscale structure having a large number of nano-scale pores and micro-scale height, AAO is widely used as the template for fabrication of nanofibers and nanotubes with a high aspect ratio27,28,29,30. However, because of the surface tension at such a high aspect ratio, nanofibers tend to easily aggregate31,32,33. Existing research has proved that nanofibers having an aspect ratio greater than 15:1 do not stand upright but instead aggregate, whereas those having a ratio less than 5:1 are individually isolated without aggregation33,34. Capillary force and surface tension play an important role upon the removal of alumina using an etchant, which is one of the processes during nanofiber fabrication. When aspect ratio increases, surface tension among nanofibers tends to pull them closer to one another, causing aggregation. Several studies have focused on methods to prevent such aggregation35, which is particularly observed in polymer and metallic nanofibers. Among these, hydration of the nanofiber surface may reduce the agglomeration because when a liquid occupies the spaces between nanofibers, surface tension decreases. Further, the freeze-drying method may also reduce aggregation by decreasing surface tension between nanofibers. However, despite various efforts, the straightening of nanofibers with a high aspect ratio remains a challenge.

To this end, we report a unique method for fabricating multiscale structures of tangled nanofiber by exploiting the aggregation phenomenon in a positive manner. Here, the nanofiber structure is imprinted using an AAO filter and polyurethane-acrylate (PUA)-type resins with a viscosity of 257.4 cP. After UV nano imprint lithography (UV-NIL) is performed, the mold is etched with a NaOH solution. To characterize the proposed multiscale structures, we investigate the pattern behaviors of the sample with aggregated nanofibers and the surface wettability after proper surface treatments such as coating with a self-assembled monolayer and UV ozone treatment. Furthermore, we propose that the multiscale porous surface can be converted simply to a slippery surface using a lubricant-infused process.

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Protocol

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1. Fabrication of Nano-Micro Multiscale Structure Surface Using an AAO Filter (Figure 1)

  1. Purchase an AAO filter with a pore size, height, and diameter of 200 nm, 60 µm, and 25 mm, respectively.
  2. 1.2. Clean the surface of the Polyethylene terephthalate (PET) film having a thickness of 100 μm to use acetone with 99.8% and isopropyl alcohol (IPA) with 99.9% for 5 min, and completely dry for 3 min using an air gun.
  3. Place the PET film on a flat surface without contaminants, and add a 0.1 mL drop of UV-curable polyurethane-acrylate (PUA)-type resin with a viscosity of 257.4 cPs onto the surface.
  4. Place the AAO filter on the resin and press uniformly, using a rubber roller with a diameter of 32 mm. The spread of the resin is visually confirmed, so the roller must be repeatedly and carefully pushed when pressing.
    CAUTION: The AAO filter is brittle and may break if excessive force is applied.
  5. After rolling, expose the specimen made with the PET and AAO filter (attached using the resin) to UV light with a wavelength of 365 nm for 30 s to cure the resin.
  6. Immerse the cured specimen in 100 mL of 2 M NaOH solution for 10 min to dissolve the filter.
    NOTE: The SEM images show the cross-section and surface of the structure (Figure 2).
  7. Clean the specimen with DI water, then completely dry it for 3 min using an air gun.
    NOTE: EDX analysis confirmed that Na and Al were not detected and were completely etched (Figure 3).

2. Surface Treatments

  1. UV ozone treatment
  2. Clean the specimen with nano-micro multiscale structures using IPA and DI water for 5 min, then dry it using an air gun for 3 min.
  3. Irradiate the side of the multiscale structures of the specimen (the side with multiscale structures) using UV rays (wavelength of 185-254 nm) for 60 min.
    NOTE: The UV ozone equipment has an intensity of 25 mW/cm2.
  4. Octadecyltrichlorosilane (OTS) self-assembly
  5. Place a hot plate inside the glove box and maintain a N2 environment for a vapor deposition process.
  6. Fix the edge of the specimen on a glass or flat plate using adhesive tape. Ensure that the size of the glass or plate is large enough to cover the top of a beaker (with 8 mm of diameter and 13 mm of height).
  7. Place the beaker on the hot plate with 5"x7" and add 2 mL of OTS solution tothe beaker using a pipette.
  8. Cover the beaker with the glass or plate face-on, with the specimen facing downward into the beaker.
  9. Process for 60 min at 100 °C, then remove the specimen from the glove box.
    NOTE: After the OTS-coating process, the beaker and glove box must be cleaned.

3. Fabrication of Functional Surface by Injecting Lubricants

  1. Deposit approximately 0.2 mL of perfluorocarbon (PFC) liquid onto the OTS-coated self-aggregated nanofiber assembly.
  2. Observe the wetting process of PFC using an optical microscope with an objective lens at 5X-20X.
  3. Remove the excess PFC liquid by placing the samples in a vertical position for a few hours.

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Results

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We demonstrated a fast and simple method for the fabrication of multiscale nano-micro hybrid structures using an AAO filter as an imprinting mold. The entire process took 30 min (Figure 4). It was noted that after undergoing the etching process using NaOH, the resultant surface exhibited an opaque color similar to the original AAO filter, owing to the aggregated nanofiber assembly caused by surface tension. Further, the results of the EDX analysis confirmed t...

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Discussion

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The key step in fabrication of the self-aggregated nanofiber assembly is to ensure that the brittle AAO filter does not break when applying the resin with the rubber rollers. In fact, it should be ensured that the AAO filter does not break at any point before the etching step. Because the AAO filter is 25 mm in diameter, the size of the substrate is approximately 30 x 30 mm.

The self-aggregated nanofiber assembly allows us to provide various functional surfaces through the proper surface treat...

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Disclosures

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The authors have no competing financial interests to disclose.

Acknowledgements

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This material is based on work supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2017R1A2B4008053) and the Ministry of Trade, Industry and Energy (MOTIE, Korea) under Industrial Technology Innovation Program No. 10052802 and the Korea Institute for the Advancement of Technology (KIAT) through the Encouragement Program for The Industries of Economic Cooperation Region (N0002310).

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
MINS 511RMMinuta TechUV curable resin
Octadecyltrichlorosilane (OTS)AldrichSurface treatment
Sodium oxidanideSAMCHUNEtching solution
Anopore Inoganic MembranesWhatman25mm/0.2µm
MT-UV-A 47Meiji TechnoUV curing equipment
UVC-30Jaesung EngineeringUVO treatment equipment
Smart Drop PlusFEMTOFABContact angle measurement
Fluorinert FC-703Mliquid mixture of completely fluorinated aliphatic compounds
Polyethylene terephthalate filmSunchemSubstrate
Acetone (99.8%)DaejungCleaning solution
Isopropyl alcohol (99.9%)DaejungCleaning solution
Rubber rollerHwahongFor application of resin
Corning Stirring Hot PlatesCorningHot plate equipment (5" x 7")

References

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,
  1. Elghanian, R., Storhoff, J. J., Mucic, R. C., Letsinger, R. L., Mirkin, C. A. Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles. Science. 277, 1078-1081 (1997).
  2. Berdichevsky, Y., Lo, Y. H. Polypyrrole nanowire actuators. Advanced Materials. 18, 122-125 (2006).
  3. Mitchell, D. T., et al. Smart nanotubes for bioseparations and biocatalysis. Journal of the American Chemical Society. 124, 11864-11865 (2002).
  4. Nicewarner-Pena, S. R., et al. Submicrometer metallic barcodes. Science. 294, 137-141 (2001).
  5. Dersch, R., Steinhart, M., Boudriot, U., Greiner, A., Wendorff, J. H. Nanoprocessing of polymers: applications in medicine, sensors, catalysis, photonics. Polymers for Advanced Technologies. 16, 276-282 (2005).
  6. Baker, L. A., Jin, P., Martin, C. R. Biomaterials and biotechnologies based on nanotube membranes. Critical reviews in solid state and materials sciences. 30, 183-205 (2005).
  7. Xiang, H., et al. Block copolymers under cylindrical confinement. Macromolecules. 37, 5660-5664 (2004).
  8. Fei, G., et al. Electro-activated surface micropattern tuning for microinjection molded electrically conductive shape memory polyurethane composites. RSC Advances. 3, 24132-24139 (2013).
  9. Kim, K., et al. Stretchable and transparent electrodes based on in-plane structures. Nanoscale. 7, 14577-14594 (2015).
  10. Kim, J., et al. Wearable smart sensor systems integrated on soft contact lenses for wireless ocular diagnostics. Nature Communications. 8, 14997(2017).
  11. Park, J., et al. Wearable, wireless gas sensors using highly stretchable and transparent structures of nanowires and graphene. Nanoscale. 8, 10591-10597 (2016).
  12. An, B. W., et al. High-resolution printing of 3D structures using an electrohydrodynamic inkjet with multiple functional inks. Advanced Materials. 27, 4322-4328 (2015).
  13. Kim, M., et al. Fully-integrated, bezel-less transistor arrays using reversibly foldable interconnects and stretchable origami substrates. Nanoscale. 8, 9504-9510 (2016).
  14. Zhao, Y. S., Zhan, P., Kim, J., Sun, C., Huang, J. Patterned growth of vertically aligned organic nanowire waveguide arrays. American Chemical Society Nano. 4, 1630-1636 (2010).
  15. Kuo, C. W., Shiu, J. Y., Chen, P. Size-and shape-controlled fabrication of large-area periodic nanopillar arrays. Chemistry of Materials. 15, 2917-2920 (2003).
  16. Lee, S. B., Koepsel, R., Stolz, D. B., Warriner, H. E., Russell, A. J. Self-assembly of biocidal nanotubes from a single-chain diacetylene amine salt. Journal of the American Chemical Society. 126, 13400-13405 (2004).
  17. Gibson, J. M. Reading and writing with electron beams. Physics Today. 50, 56-61 (1997).
  18. Kramer, N., Birk, H., Jorritsma, J., Schönenberger, C. Fabrication of metallic nanowires with a scanning tunneling microscope. Applied Physics Letters. 66, 1325-1327 (1995).
  19. Jiang, P., Bertone, J. F., Colvin, V. L. A lost-wax approach to monodisperse colloids and their crystals. Science. 291, 453-457 (2001).
  20. Steinhart, M., et al. Polymer nanotubes by wetting of ordered porous templates. Science. 296, 1997(2002).
  21. Hong, S. H., Hwang, J., Lee, H. Replication of cicada wing's nano-patterns by hot embossing and UV nanoimprinting. Nanotechnology. 20, 385303(2009).
  22. Han, K. S., Shin, J. H., Yoon, W. Y., Lee, H. Enhanced performance of solar cells with anti-reflection layer fabricated by nano-imprint lithography. Solar Energy Materials and Solar Cells. 95, 288-291 (2011).
  23. Choo, S., Choi, H. J., Lee, H. Replication of rose-petal surface structure using UV-nanoimprint lithography. Materials Letters. 121, 170-173 (2014).
  24. Yu, Z., Chou, S. Y. Triangular profile imprint molds in nanograting fabrication. Nano Letters. 4, 341-344 (2004).
  25. Hirai, Y., Harara, S., Isaka, S., Kobayashi, M., Tanaka, Y. Nano-Imprint lithography using replicated mold by Ni electroforming. Japanese Journal of Applied Physics. 41, 4186(2002).
  26. Kim, J. H., Cho, Y. T., Jung, Y. G. Selection of absorptive materials for non-reflective wire grid polarizers. International Journal of Precision Engineering and Manufacturing. 17, 903-908 (2016).
  27. St˛epniowski, W. J., Salerno, M. Fabrication of nanowires and nanotubes by anodic alumina template-assisted electrodeposition. Manufacturing Nanostructures. 12, 321-357 (2014).
  28. Sousa, C. T., et al. Nanoporous alumina as templates for multifunctional applications. Applied Physics Reviews. 1, 031102(2014).
  29. Hong, S. H., Bae, B. J., Lee, H., Jeong, J. H. Fabrication of high density nano-pillar type phase change memory devices using flexible AAO shaped template. Microelectronic Engineering. 87, 2081-2084 (2010).
  30. Schwirn, K., et al. Self-ordered anodic aluminum oxide formed by H2SO4 hard anodization. American Chemical Society Nano. 2, 302-310 (2008).
  31. Lee, P. S., et al. Vertically aligned nanopillar arrays with hard skins using anodic aluminum oxide for nano imprint lithography. Chemistry of Materials. 17, 6181-6185 (2005).
  32. Lopes, M. C., de Oliveira, C. P., Pereira, E. C. Computational modeling of the template-assisted deposition of nanowires. Electrochimica Acta. 53, 4359-4369 (2008).
  33. Choi, M. K., Yoon, H., Lee, K., Shin, K. Simple fabrication of asymmetric high-aspect-ratio polymer nanopillars by reusable AAO templates. Langmuir. 27, 2132-2137 (2011).
  34. Kim, Y. S., Lee, K., Lee, J. S., Jung, G. Y., Kim, W. B. Nanoimprint lithography patterns with a vertically aligned nanoscale tubular carbon structure. Nanotechnology. 19, 365305(2008).
  35. Chen, G., Soper, S. A., McCarley, R. L. Free-standing, erect ultrahigh-aspect-ratio polymer nanopillar and nanotube ensembles. Langmuir. 23, 11777-11781 (2007).
  36. Jeong, Y., et al. Fabrication of Nano-Micro Hybrid Structures by Replication and Surface Treatment of Nanowires. Crystals. , (2017).

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Tags

Anodic Aluminum OxideImprint ProcessSelf AggregationNanofiber AssemblySurface MorphologyWettability AnalysisUV Ozone TreatmentSelf Assembled Monolayer

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