Electrospinning onto Insulating Substrates by Controlling Surface Wettability and Humidity

Nanoscale Research Letters, Nov 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.

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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)


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WooSeok Choi, Geon Hwee Kim, Jung Hwal Shin, Geunbae Lim, Taechang An. Electrospinning onto Insulating Substrates by Controlling Surface Wettability and Humidity, Nanoscale Research Letters, 2017, pp. 610, Volume 12, Issue 1, DOI: 10.1186/s11671-017-2380-6