- Nano Express
- Open Access
Electrospinning onto Insulating Substrates by Controlling Surface Wettability and Humidity
© The Author(s). 2017
- Received: 4 July 2017
- Accepted: 21 November 2017
- Published: 28 November 2017
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 near-field electrospinning onto a hydrophilic surface.
- Surface wettability
- Thin film water
- Insulator substrate
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.  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.  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.  reported electrospinning onto an insulating polymer substrate (polyethylene terephthalate) using an AC pulse-modulated 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 . 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.
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) . 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
Local Humidity Control
To increase the humidity in the immediate vicinity of the polymer substrate, a wet paper was placed between the polymer substrate and the ground electrode (Fig. 1b). The humidity was relatively high only around the polymer substrate due to the low diffusivity of water vapor. The humidity around the electrospinning syringe tip was about 50%, while the humidity around the polymer substrate was about 70% (Additional file 1: Figure S2). It has been shown that water molecule adsorption onto the surface of hydrophilic polymers increases rapidly when the relative humidity exceeds 50% .
The Force Acting on CNTs at the Liquid–Air Interface
We investigated two modes of electrospinning: a tip-to-electrode distance of 8 cm and applying 13 kV DC voltage with a fixed tip (far-field electrospinning), and a tip-to-electrode distance of 1 cm and applying 2 kV DC voltage with a moving tip (near-field electrospinning).
We introduced a novel method for electrospinning onto an insulating substrate regardless of substrate thickness. Plasma treatment of an acrylic substrate produces a hydrophilic surface. In an appropriately high-humidity environment, water molecules adsorb to form a thin layer that acts as a ground electrode. Electrospun nanofibers were deposited on a flexible polymer substrate using this method and there was no significant difference from the morphology of electrospun fiber from conventional electrospinning. It was also shown that polymer fibers could be written directly on hydrophilic surfaces of hydrophobic substrates using near-field electrospinning. Increasing the local humidity around the polymer substrate enabled electrospinning onto the insulator surface. This interesting result contrasts with the general assumption that electrospinning should be performed at low humidity. Specific regions of a polymer substrate can be defined for electrospun fiber deposition by selectively controlling the wettability of the substrate. Therefore, fiber patterns are possible without the relatively complex and expensive processes, such as microelectromechanical system (MEMS)-based techniques, currently used to fabricate micropatterned electrodes. Moreover, we believe that electrospinning using conductive materials such as carbon nanotubes or conducting polymers may be applicable to fabricating electrodes on flexible substrates that can be used in wearable devices.
This work was supported by Korea National University of Transportation in 2016 and National Research Foundation of Korea (NRF) grants funded by the Korean Government (MSIP) (NO. 2015R1A2A2A01006496).
WC, GHK, and TA conceived of the study and participated in its design. GHK and TA participated in the fabrication of selective hydrophobic surface. WC and TA carried out electrospinning experiments. WC, JHS, and GB wrote this manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Huang Z-M, Zhang Y-Z, Kotaki M, Ramakrishna S (2003) A review on polymer nanofibers by electrospinning and their applications in nanocomposites. Compos Sci Technol 63:2223–2253View ArticleGoogle Scholar
- Teo WE, Ramakrishna S (2006) A review on electrospinning design and nanofibre assemblies. Nanotechnology 17:R89–R106View ArticleGoogle Scholar
- Zhang C-L, Yu S-H (2014) Nanoparticles meet electrospinning: recent advances and future prospects. Chem Soc Rev 43:4423–4448View ArticleGoogle Scholar
- Mirjalili M, Zohoori S (2016) Review for application of electrospinning and electrospun nanofibers technology in textile industry. J Nanostruct Chem 6:207–213View ArticleGoogle Scholar
- Ramakrishna S, Fujihara K, Teo WE, Lim TC & Zuwei Ma: An introduction to Electrospinning and Nanofibers. (World Scientific Publishing Company, 2005)View ArticleGoogle Scholar
- Cho SJ, Kim B, An T, Lim G (2010) Replicable multilayered nanofibrous patterns on a flexible film. Langmuir 26:14395–14399View ArticleGoogle Scholar
- Zheng J-Y et al (2014) Electrohydrodynamic direct-write orderly micro/nanofibrous structure on flexible insulating substrate. J Nanomater:1–7Google Scholar
- Min S-Y et al (2013) Large-scale organic nanowire lithography and electronics. Nat Commun 4:1773View ArticleGoogle Scholar
- Heo J et al (2016) Enhanced cellular distribution and infiltration in a wet electrospun three-dimensional fibrous scaffold using eccentric rotation-based hydrodynamic conditions. Sensors Actuators B Chem 226:357–363View ArticleGoogle Scholar
- Smit E, Bűttner U, Sanderson RD (2005) Continuous yarns from electrospun fibers. Polymer 46:2419–2423View ArticleGoogle Scholar
- Yokoyama Y et al (2009) Novel wet electrospinning system for fabrication of spongiform nanofiber 3-dimensional fabric. Mater Lett 63:754–756View ArticleGoogle Scholar
- Park SM, Kim DS (2015) Electrolyte-assisted electrospinning for a self-assembled, free-standing nanofiber membrane on a curved surface. Adv Mater 27:1682–1687View ArticleGoogle Scholar
- Beaglehole D (1997) Aspects of vapor adsorption on solids. Physica A: Statistical Mechanics and its Applications 244:40–44View ArticleGoogle Scholar
- Johnston EE, Ratner BD (1996) Surface characterization of plasma deposited organic thin films. J Electron Spectrosc Relat Phenom 81:303–317View ArticleGoogle Scholar
- Vogt BD, Soles CL, Lee H-J, Lin EK, Wu W (2005) Moisture absorption into ultrathin hydrophilic polymer films on different substrate surfaces. Polymer 46:1635–1642View ArticleGoogle Scholar
- Li D, Wang Y, Xia Y (2003) Electrospinning of polymeric and ceramic nanofibers as uniaxially aligned arrays. Nano Lett 3:1167–1171View ArticleGoogle Scholar
- Reneker DH, Yarin AL, Fong H, Koombhongse S (2000) Bending instability of electrically charged liquid jets of polymer solutions in electrospinning. J Appl Phys 87:4531–4547View ArticleGoogle Scholar
- Lauricella M, Cipolletta F, Pontrelli G, Pisignano D, Succi S (2017) Effects of orthogonal rotating electric fields on electrospinning process. Phys Fluids 29:082003View ArticleGoogle Scholar
- Wang H, Zheng G, Li W, Wang X, Sun D (2011) Direct-writing organic three-dimensional nanofibrous structure. Appl Phys A Mater Sci Process 102:457–461View ArticleGoogle Scholar