Electrospinning onto Insulating Substrates by Controlling Surface Wettability and Humidity
Choi et al. Nanoscale Research Letters
Electrospinning onto Insulating Substrates by Controlling Surface Wettability and Humidity
WooSeok Choi 3
Geon Hwee Kim 2
Jung Hwal Shin 1
Geunbae Lim 2
Taechang An 0
0 Department of Mechanical Design Engineering, Andong National University , Kyungbuk 760-749 , Republic of Korea
1 Biomedical Engineering, School of Life Sciences, Ulsan National Institute of Science and Technology (UNIST) , 50, UNIST-gil, Ulsan 44919 , Republic of Korea
2 Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH) , Pohang 790-784 , Republic of Korea
3 Department of Mechanical Engineering, Korea National University of Transportation , Chungju, Chungcheongbuk-do 380-702 , Republic of Korea
We report a simple method for electrospinning polymers onto flexible, insulating substrates by controlling the wettability of the substrate surface. Water molecules were adsorbed onto the surface of a hydrophilic polymer substrate by increasing the local humidity around the substrate. The adsorbed water was used as the ground electrode for electrospinning. The electrospun fibers were deposited only onto hydrophilic areas of the substrate, allowing for patterning through wettability control. Direct writing of polymer fiber was also possible through nearfield electrospinning onto a hydrophilic surface.
Electrospinning; Nanofibers; Surface wettability; Thin film water; Insulator substrate
Background
Electrospinning is a technique used to produce
continuous fibers, with diameters of several hundred
nanometers, using an electric field. Electrospinning is relatively
inexpensive and has been applied to a wide variety of
applications and materials [
1–4
]. The electrospinning setup
consists primarily of three parts: a high-voltage source, a
spinneret, and a collector. The collector is generally a
conductive substrate, such as a metal, that functions as
the ground electrode and helps form a stable electric
field in the spinneret. When non-conductive substrates
are used as collectors, conductive ground electrodes
must be placed on the substrate surface [
4, 5
].
Many industrial applications of electrospun nanofibers
require their deposition onto insulating substrates, such as
flexible polymers [
6, 7
]. Cho et al. [6] demonstrated the
deposition of electrospun nanofibers onto thin, flexible
insulator layers on an electrode. Electrospun nanofibers
deposited under such circumstances will follow or align with
the underlying electrodes. Min et al. [
8
] produced
patterned organic semiconducting nanowires on a polymer
substrate using near-field electrospinning. In both cases,
electrospinning onto the polymer substrate was only
possible if the insulating layer was thin enough (less than
100 μm) to maintain a high electric field. Zheng et al. [
7
]
reported electrospinning onto an insulating polymer
substrate (polyethylene terephthalate) using an AC
pulsemodulated electrohydrodynamic method. This method is
capable of electrospinning onto polymer substrates
regardless of substrate thickness, but requires the
application of a relatively complex AC electric field. While the
aforementioned studies have demonstrated feasibility,
electrospinning onto non-conductive surfaces has not
attained widespread use in industrial applications.
Here, we present a novel method for electrospinning
fibers onto insulating substrates that overcomes the
limitations of previous work. Electrospinning has been
demonstrated using a liquid electrolyte as the collector
electrode [
9–12
]. Also note that, at an appropriately high
humidity, water molecules will adsorb to a hydrophilic
surface and begin to conduct electricity at approximately
one monolayer [13]. If the proper humidity is
maintained around an insulating substrate with a hydrophilic
surface, then water molecules adsorbed on the surface
can serve as an electrode layer, allowing the deposition
of electrospun fibers. Unlike previous studies, this
method is independent of substrate thickness because it
relies only on the surface characteristics of the substrate
in the surrounding environment. Moreover, it is
compatible with conventional electrospinning techniques,
requiring only humidity control.
Methods
Preparation of Polymer Substrate with a Hydrophilic
In this experiment, a 500-μm acrylic substrate with an
originally hydrophobic surface was used as the collector.
Oxygen plasma treatment (CUTE, Femto Science,
Korea) for 30 s of the acrylic substrate resulted in a
hydrophilic surface populated with silanol groups
(SiOH) [
14
]. This reaction was confirmed by a change in
water contact angle from 81.3° on pristine acrylic to
36.7° after plasma treatment (Additional file 1: Figure
S1b–d). Regions of the acrylic substrate were selectively
made hydrophilic by applying a stencil mask prior to
plasma treatment (Additional file 1: Figure S1a).
Preparations for Electrospinning
Electrospinning was performed at room temperature
and moderate humi (...truncated)