Multiscale Structures Aggregated by Imprinted Nanofibers for Functional Surfaces

Summary

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

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

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 engineering^{1,2,3,4,5,6,7,8}. In particular, nanofibers are widely used in stretchable and transparent electrodes⁹, wearable senso....

Protocol

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.

Results

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.......

Discussion

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.......

Materials

List of materials used in this article

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