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).

1. Fabrication of Nano-Micro Multiscale Structure Surface Using an AAO Filter (Figure 1)
<ol>
	<li>Purchase an AAO filter with a pore size, height, and diameter of 200 nm, 60 &#181;m, and 25 mm, respectively.</li>
	<li>1.2. Clean the surface of the Polyethylene terephthalate (PET) film having a thickness of 100 &#956;m 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.</li>
	<li>Place the PET film on a flat surface wit...

<ol>
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The authors have no competing financial interests to disclose.

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...

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&#160;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.

<table>
	<tbody>
		<tr>
			<td>MINS 511RM</td>
			<td>Minuta Tech</td>
			<td></td>
			<td>UV curable resin</td>
		</tr>
		<tr>
			<td>Octadecyltrichlorosilane (OTS)</td>
			<td>Aldrich</td>
			<td></td>
			<td>Surface treatment</td>
		</tr>
		<tr>
			<td>Sodium oxidanide</td>
			<td>SAMCHUN</td>
			<td></td>
			<td>Etching solution</td>
		</tr>
		<tr>
			<td>Anopore Inoganic Membranes</td>
			<td>Whatman</td>
			<td></td>
			<td>25mm/0.2&#181;m</td>
		</tr>
		<tr>
			<td>MT-UV-A 47</td>
			<td>Meiji Techno</td>
			<td></td>
			<td>UV curing equipment</td>
		</tr>
		<tr>
			<td>UVC-30</td>
			<td>Jaesung Engineering</td>
			<td></td>
			<td>UVO treatment equipment</td>
		</tr>
		<tr>
			<td>Smart Drop Plus</td>
			<td>FEMTOFAB</td>
			<td></td>
			<td>Contact angle measurement</td>
		</tr>
		<tr>
			<td>Fluorinert FC-70</td>
			<td>3M</td>
			<td></td>
			<td>liquid mixture of completely fluorinated aliphatic compounds</td>
		</tr>
		<tr>
			<td>Polyethylene terephthalate film</td>
			<td>Sunchem</td>
			<td></td>
			<td>Substrate</td>
		</tr>
		<tr>
			<td>Acetone (99.8%)</td>
			<td>Daejung</td>
			<td></td>
			<td>Cleaning solution</td>
		</tr>
		<tr>
			<td>Isopropyl alcohol (99.9%)</td>
			<td>Daejung</td>
			<td></td>
			<td>Cleaning solution</td>
		</tr>
		<tr>
			<td>Rubber roller</td>
			<td>Hwahong</td>
			<td></td>
			<td>For application of resin</td>
		</tr>
		<tr>
			<td>Corning Stirring Hot Plates</td>
			<td>Corning</td>
			<td></td>
			<td>Hot plate equipment (5&#34; x 7&#34;)</td>
		</tr>
	</tbody>
</table>

multiscale structures aggregated by imprinted nanofibers for functional surfaces

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.

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...

Watch this Scientific Journal Video about Multiscale Structures Aggregated by Imprinted Nanofibers for Functional Surfaces at JoVE.com

Multiscale Structures Aggregated by Imprinted Nanofibers for Functional Surfaces

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

Multiscale surface structures have attracted increasing interest owing to several potential applications in surface devices. However, an existing ...

This method can help answer key questions in the engineer to surface field in understanding functional surface for tubular morphology and wettability. The main advantage of our approach is that it allows faster fabrication of multiscale nanomicro structures by using only an imprint process with an anodic aluminum oxide filter and a self-aggregation of nano fibers. After imprinting, the replicated surface patterns initially exhibited superhydrophilicity.We can change the surface availability of the imprinted structures by using UV origin treatment and self-assembled monolayer coating. Obtain an anodic aluminum oxide, or AAO, filter with a pore size of 200 nanometers, height of 60 microns, and diameter of 25 milliliters. Clean the surface with polyethylene terephthalate, or PET film, with 99.8%acetone for five minutes, followed by 99.9.isopropyl alcohol for five minutes. Completely dry the film for three minutes using an air gun. Next, place the PET film on a flat surface without contaminants.Add a 0.1 milliliter drop of UV curable polyurethane acrylate type resin with a viscosity of 257.4 CPS on the surface. Place the AAO filter on the resin and press uniformly using a rubber roller with a diameter of 32 millimeters. The spread of the resin is visually confirmed.The roller must be repeated and carefully pushed when pressing. The AAO filter is brittle and may break if excessive force is applied. After rolling, expose the specimen made with the PET and AAO filter to UV light with a wavelength of 365 nanometers for 30 seconds to cure the resin.Then, immerse the cured specimen in 100 milliliters of two molar sodium hydroxide solution for 10 minutes to dissolve the filter. The SEM images show the surface and cross section of the structure. Clean the specimen with deionized water.Then, completely dry it for three minutes using an air gun. Use energy dispersive x-ray analysis to confirm that sodium and aluminum are not detected and are completely etched. To perform the UV ozone treatment, first clean the specimen with nanomicro multiscale structures using isopropyl alcohol for five minutes and then deionized water for five minutes.Dry the washed the specimen using an air gun for three minutes. Irradiate the specimen using UV rays for 60 minutes using UV ozone equipment with an intensity of 25 milliwatts per square centimeter. For OTS self-assembly, place the hot place inside the glovebox, and maintain a nitrogen environment for the vapor deposition process.For filming purposes we will demonstrate the procedure in mock outside a glovebox. Place a beaker on the hot plate and add two milliliters of OTS solution to the beaker using a pipette. Cover the beaker with the glass or plate face on, with the specimen facing downward into the beaker.Process for 60 minutes at 100 degrees Celsius before removing the specimen from the glovebox. To fabricate the functional surface by injecting lubricants, deposit approximately 0.2 milliliters per square centimeter of perfluorocarbon liquid on the OTS coated self-aggregated nanofiber assembly. Observe the wetting process of the perfluorocarbon using an optical microscope at five to 20 times magnification.Finally, remove the excess perfluorocarbon liquid by placing the sample in a vertical position for a few hours. Multiscale nanomicro hybrid structures obtained by the imprint process and evaporation derived self-aggregation are shown here. It is difficult to measure the contact angle because of the superhydrophilicity of the fabricated surface.Interestingly, after UV ozone treatment with sufficient time, the surface morphology and the surface wettability change from superhydrophilicity to hydrophobicity, with a contact angle of 126.8 degrees. Further more, the contact angle can be increased to 133.6 degrees by an additional coating of the self-assembled monolayer. After its development, this technique paved the way for researchers in the field of engineered surface to explore the surface functionality and morphology change with the self-assembly phenomenon and proper surface treatment.Though this method can provide insight into the modification of the surface morphology and wettability, it can also be applied to other applications such as tissue via scalpel, environmental filters, catalyst disruptor, or with diffused optics, because of its larger scale porous structures.

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JoVE Journal

Engineering

6.5K vistas.  Changwon National University. This method can help answer key questions in the engineer to surface field in understanding functional surface for tubular morphology and wettability. The main advantage of our approach is that it allows faster fabrication of multiscale nanomicro structures by using only an imprint process with an anodic aluminum oxide filter and a self-aggregation of nano fibers. After imprinting, the replicated surface patterns initially exhibited superhydrophilicity.We can change the surface availab...