Three-Dimensional Highly Stretchable Conductors from Elastic Fiber

Subscriber access provided by Eastern Michigan University | Bruce T. Halle Library

Article

Three-Dimensional Highly Stretchable Conductors from Elastic Fiber Mat with Conductive Polymer Coating Shasha Duan, Zhihui Wang, Ling Zhang, Jin Liu, and Chunzhong Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b08453 • Publication Date (Web): 16 Aug 2017 Downloaded from http://pubs.acs.org on August 18, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Three-Dimensional Highly Stretchable Conductors from Elastic Fiber Mat with Conductive Polymer Coating Shasha Duan, Zhihui Wang, Ling Zhang,* Jin Liu, Chunzhong Li* School of Materials Science and Engineering, Key Laboratory for Ultrafine Materials of Ministry of Education, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, P. R. China KEYWORDS.

three-dimensional

structure,

polyurethane

fiber

mat,

poly(3,4-

ethylenedioxythiophene), stretchable, conductive

ABSTRACT. The manufacture of stretchable conductors with well-reserved electrical performance under large-degree deformations via scalable processes remains of great importance. In this work, a highly stretchable 3D conductive framework consisted of polyurethane fiber mat (PUF) and poly(3,4-ethylenedioxythiophene) (PEDOT) is reported through facile approaches, electrospinning and in situ interfacial polymerization, which was then backfilled with poly(dimethylsiloxane) to obtain 3D conductors. The excellent stretchability of the 3D conductive network imparted the as-prepared electrode superior mechanical durability. What’s more, the applied strains can be effectively accommodated by the arrangement and orientation of the fibers resulting in relatively stable electrical performance with only 20%

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 23

increased resistance at 100% stretching. Meanwhile, the resistance of the conductor could keep constant during 2000 times of bending and showed slightly increase during 100 times of 50% stretching. The potential in the applications of large-area stretchable electrodes were demonstrated by the construction of LED arrays with the PUF based conductors as electrical connections.

INTRODUCTION Stretchable conductive materials (SCMs) are of significant importance in next-generation electronics such as stretchable displays, artificial skins, strain and pressure sensors, and so on.1-11 Except the application of sensors, in most cases, a key element to evaluate SCMs is whether they are capable of retaining electrical conductivity under large bending, twisting and stretching deformations.12-20 Rigid conductive materials were transferred onto pre-strained polymer substrates to form stretchable wavy structure, revealing high conductivity but relatively poor stretchability.21-22 An inevitable decrease in conductivity under even low strain of 20% was common phenomenon in composites with silicon as conductive components due to their inherent stiffness. How to retain the electrical conductivity at high strains to satisfy requirements remains a great challenge. In comparison, 3D stretchable conductor made from 3D conductive skeleton including carbon nanotubes (CNTs), graphene or metal nanowires, was demonstrated to be a more competitive one due to its considerable mechanical durability. More importantly, the particular 3D structure is capable of accommodating part of the applied strain by the shape deformation and keeping the conductive pathway from breaking to some extent. One common and effective approach to acquire 3D stretchable electrode is to backfill poly(dimethylsiloxane) (PDMS) into the pre-made conductive network. Featuring remarkable electrical conductivity and flexibility, conductive


2

Page 3 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


aerogel is regarded as a good 3D conductive network. Nevertheless, even though they are bendable and compressible, the limited stretchability makes this kind of conductive network easy to crack under high stretching. For example, a CuNWs aerogel/PDMS electrode exhibited a maximum strain of 60%, and a CNTs/graphene aerogel/PDMS electrode in our previous work showed 30% decreased conductivity at a low stretching of 30%, which restricted their applications in the electronics that need to operate at high-degree deformations.23-24 In order to achieve superior stretchability, 3D stretchable electrodes are also prepared by the combination of a 3D porous elastomer and conductive components. J. Park et al. offered a novel 3D porous PDMS with enhanced elongation by using photolithography technique.25 Due to the special 3D structure, the applied strain was partly undertaken by the rotation of the bridging elements resulting in well-retained electrical conductivity after the infilling of liquid metal. In addition, nickel foam and 3D printing technique were also employed to produce 3D porous PDMS in our previous work and the resulted products both performed well under large strains.2627

Unfortunately, the fabrication processes of this kind of 3D porous elastomer are either high-

cost or complicated, which added difficulty to their realistic applications in stretchable electronics. On the other hand, due to continuous macropores and noticeable commercial availability, polyurethane sponge (PUS) is an alternative 3D porous elastomer with good practicality.28-31 For instance, J. Ge et al. prepared a binary-network-based stretchable electrode PUS-AgNWs-PDMS by using PU sponge as the support of 2D AgNWs network. Nevertheless, the limited elongation rate of and the inherent defects the commercial PUS make the conductive framework easily break at large strains, and thus the PUS-AgNWs-PDMS electrode showed obvious resistance increase of 160% at 100% stretching.32 At present, both high stretchability and well-reserved electrical conductivity are still far less than the requirements for practical


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 23

applications. Moreover, the large-area fabrication of the conductors via a scalable process is demanded. Here, a highly stretchable and defect-free PU fiber mat (PUF) is creatively developed by electrospining, followed by the integration of poly(3,4-ethylenedioxythiophene) (PEDOT) coating to serve as the 3D conductive network. Compared to the conductive network based on PUS, the superior stretchability (>300%) of the PUF/PEDOT fabricated in this work imparts the skeletons better mechanical durability at large strains and therefor well-retained conductive pathway. In order to further improve the resilience and strength of the PUF/PEDOT, PDMS was employed to encapsulate the conductive framework resulting in a high-performance 3D stretchable conductor. Owing to the extraordinary framework of PUF/PEDOT, the applied strains were adapted via the rearrangement and orientation of the fibers, and consequently the resistance of the as-prepared PUF/PEDOT/PDMS showed a small increment of 20% at a large stretching of 100%. Meanwhile, the composite exhibited outstanding endurance after cyclic deformations: the resistance kept stable after 2000 bendings and slightly increased after 100 times of the 50% stretching-releasing process. Besides, a bendable and stretchable 2*4 LED arrays were successfully manufactured with the 3D conductive composites as interconnections. Both of the scalable fabrication process and the ascendant performance of the PUF/PEDOT/PDMS composite makes it a potential candidate in the applications of the nextgeneration stretchable electronics.

EXPERIMENTAL METHODS Fabrication of PUF. PU solution (10 wt%) was prepared by adding PU pellets to DMF/THF mixed solvent with weight ratio of 2/1. After dissolved PU at 60 °C for 1h, the mixed solution was stirred for 6h at room temperature to make a homogeneous mixture. A voltage of 15 KV was


4

Page 5 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


applied to the solution to spin the fibers out of a grounded aluminum foil. The distance from the capillary tip to the collector and the pump rate was separately set as 30cm and 1ml/h. The fibers were collected for 2 to 5h to obtain fiber mats with different thickness. The prepared fiber mat was dried at 50 °C for 3h to remove residual solvents. Fabrication of PUF/PEDOT. 0.5g FeCl3 and 0.373ml EDOT were added into 10ml ethanol followed by stirring for 2h. Then the mixed solution was added onto PU fiber mat drop by drop to make the mat fully wet. PEDOT shell gradually formed on PU fiber during the evaporation of ethanol. The conductive fiber mat was prepared until ethanol was completely evaporated. Then the obtained conductive fiber mat was washed by a lot of methanol using an ultrasound machine to remove residual reagents. Finally the conductive fiber mat was dried at 40 °C for 4h in vacuum. Fabrication of PUF/PEDOT/PDMS stretchable conductor. Copper wires were attached to the two ends of the PU/PEDOT conductive fiber mat by silver paste. Then the fiber mat was put in a glass petri dish. PDMS prepolymer prepared by mixing PDMS base agent with curing agent in a weight ratio of 10:1 was poured onto the fiber mat. After degassing in a vacuum desiccator, PDMS was cured at 60 °C for 2h. Finally, PUF/PEDOT/PDMS stretchable conductor was obtained after it was peeled off from the glass petri dish. Characterization. A field emission scanning electron microscopy (FE-SEM, Hitachi S-4800) was used to characterize the morphologies of PUF, PUF/PEDOT, PUF/PEDOT/PDMS, operating at 15 kV. Raman spectra of PUF/PEDOT was collected on a Lab Ram Infinity Raman spectrometer, using a linearly 514.5nm lasers. The electrical conductivity of PUF/PDMS composites were measured by four-point probes (model RTS-8, Guangzhou 4Probes Tech Industrial Co., Ltd., Guangzhou, China) contact direct current (dc) conductivity measurement


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 23

method. The stress versus strain properties of PUF and PUF/PEDOT composites were performed using a universal testing machine (CMT4204, Sansi Co., Ltd., China). The normalized resistance measurements under mechanical strain were taken using a motorized test stand (Mark-10, USA) combined with a Keithley 2400-C Sourcemeter (USA). The stretching and bending cycles of PUF/PEDOT/PDMS were performed by the motorized test stand (Mark-10, USA).

RESULTS AND DISSUSSION The preparation of PUF/PEDOT/PDMS is presented in Figure 1. Here, electrospinning technique, a scalable and low cost approach, was employed to produce stretchable PU fiber mat. Through adjusting the technical parameters of electrospinning, random networks consisted of PU fibers (diameter, ~1 µm) were obtained (Figure 1a). PUF with different thickness can be prepared by controlling the length of the spinning time. Then a highly conductive PEDOT shell was formed on the surface of PU fibers via in situ interfacial polymerization of EDOT. Here, PEDOT was selected as the conductive component because the hydrophobic PUF can be easily wetted by the ethanol solution of EDOT/FeCl3 and as the ethanol evaporated, the micro-sized fibers were successfully coated with PEDOT forming a core-shell structure.33-36 As shown in Figure 1b, the conductive shell is relatively uniform and no agglomerates can be observed, which also benefited the electrical conductivity of PUF/PEDOT. Additionally, our coating process showed excellent reproducibility that the pores weren’t blocked even at a very high PEDOT loading of 60 wt% (Figure S1, Supporting Information). The successful polymerization of PEDOT was further identified by Raman spectroscopy (Figure S2, Supporting Information). It is noted that after the coating process of PEDOT, the fibers become curve. This is because during the process of impregnation and washing, fibers got soft and bent in solution, and after being dried they maintained the bending state. In order to acquire excellent resilience and strength,


6

Page 7 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


PDMS was backfilled into the pores of PUF/PEDOT forming a sandwich structure. Two copper wires are separately fixed on the two ends of the sample by Ag paste before PDMS impregnation to record the electrical properties of the composite under the applied strains. Based on the crosssection SEM images of PUF/PEDOT/PDMS in Figure 1c, PDMS completely filled the pores of the fiber mat forming an integral sandwich structured stretchable conductor. The PUF prepared by electrospinning showed significantly improved mechanical performance in comparison to commercial PUS. As shown in Figure 2a, the breaking elongation of a 50-µm PUF is as high as 434% with a tensile strength of 6.3 MPa while the maximal strain of a 3-mm thick PUS is only 111% with a low strength of 0.11 MPa (shown in Figure S3, Supporting Information). Though the introduction of PEDOT caused decreased stretchability, the PUF/PEDOT (with 30 wt% PEDOT) prepared by a 50-µm PUF still possesses a high breaking elongation of 315%. The excellent mechanical performance of PUF/PEDOT demonstrated their advantage in the fabrication of 3D stretchable conductors. However, obvious hysteresis was found on PUF, which is caused by the intrinsic property of PU. Moreover, the PEDOT loading process increased the stiffness of PUF/PEDOT and led to more irreversible deformation (Figure S4, Supporting Information). For a PUF/PEDOT prepared by 50-µm PUF, when it is released from 100% stretching, up to 50% irreversible deformation was observed. Fortunately, the introduction of PDMS solved the problem and endows the conductive fiber mat with predominant resilience. The conductivity of the prepared PUF/PEDOT can be expediently controlled through regulating the loading capacity of PEDOT, which increases with the increased content of PEDOT (Figure 2b). In addition, with the same PEDOT mass fraction, thicker PUF corresponds to more conductive pathway in PUF/PEDOT and thus higher conductivity. With a 150-µm PUF


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 23

and 30 wt% PEDOT, the conductivity of PUF/PEDOT can reach 4.7 S/cm. Meanwhile, PEDOT was polymerized on PUS using the same loading process and the results show that even with a high PEDOT loading of 30 wt%, the conductivity of the PUS/PEDOT is less than 0.1 S/cm, far lower than that of PUF/PEDOT (Figure S5, Supporting Information). The distinct difference in conductivity of the two composites should be attributed to the different compact degree of the two frameworks. For commercial available PUS (Figure S6, Supporting Information), the size of skeleton and pore are 40 µm and 300 µm respectively, while the PUF in this work shows both skeleton and pore with only a few microns. It is calculated that the density of the PUF in this work is 598 mg/cm3 while that of the PUS is only 24.5 mg/cm3. The intensive conductive network of PUF/PEDOT provides more paths for electrical transmission and leads to superior electrical performance. A crucial indicator of SCMs is whether they are capable of retaining conductivity unchanged while bearing large deformations. Benefiting from the superior flexibility of PUF based conductive network, the PUF/PEDOT/PDMS composite exhibits fascinating electrical performance during the tensile process. The resistance variations of the composites (with 30 wt% PEDOT) prepared by different thickness of PUF as a function of the applied strain are shown in Figure 2c. Featuring remarkable elasticity and strength, the PUF/PEDOT/PDMS can be easily stretched to 100% without mechanical failure. Though the resistance increased inevitably during the stretching process, the increment is comparatively small. For the PUF/PEDOT/PDMS prepared by a 50-µm PUF, the resistance only increased 20% at 100% stretching. The resistance variation also increased with the increasing thickness of PUF and a 150-µm sample showed an increased resistance of 42% at 100% stretching. The worse electrical performance of thicker sample may derive from more reduced fiber nodes during stretching. As the contributor for


8

Page 9 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


electrical transmission, the joints of fibers were decreased when strain was applied to the conductive fibers especially above 50% strain. Thicker PUF/PEDOT with more joints exhibited more obviously reduced nodes, and thus larger resistance increment under stretching. With the same content of PEDOT, a PUS/PEDOT/PDMS composite (with 30 wt% PEDOT) ruptured at 70% elongation with an increased resistance of 46% （Figure S7, Supporting Information）. When compared with several other 3D stretchable conductors, our PUF/PEDOT/PDMS composite showed superior electrical performance under gradually increased strains (more reports are listed in Table S1, Supporting Information). Based on the data in Figure 2d, the PUS/CuAg/PDMS, CuNWs aerogel/PDMS as well as the rGO-AgNWs foam/PDMS electrodes showed poor stretchability with maximum strains smaller than 60%. Though the PUS/AgNWs/PDMS exhibit larger maximum strains at 100%, the resistance increased remarkably under stretching. Hence, the PUF/PEDOT/PDMS in this work possesses both excellent stretchability and well-reserved conductivity at large strains, which demonstrated the great advantage of the 3D conductive composite in our work as a stretchable conductor. In order to make full sense of the deformation mechanism of the PUF based 3D conductor, the microstructures of the PUF/PEDOT under 0%, 50%, 75% and 100% stretching were investigated by SEM observation (Figure 3b-e). Once there is an external force, the 3D conductive composite is capable of sharing the applied strain through the deformation of the fiber network and the specific mode of deformation can be divided into two stages in accordance with the images shown in Figure 3b~e: rearrangement (0~50%) and orientation (50~100%). As we mentioned before, the fibers become curve during the loading process of PEDOT shell. Hence, in the first stage, the fiber network adapts the deformation by straightening those curly fibers along the tensile direction, which can be called rearrangement. It is obviously that there are more straight


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 23

fibers at 50% elongation than those at the initial state. When further increasing the tensile strain, the fibers start to orientate along the stretching direction, which decreased the joints of the conductive fibers and resulted in larger resistance increment. Meanwhile, with the increasing strain, some of the fibers are stretched and cracks can be observed on part of the PEDOT shell at 100% stretching (shown in the inset of Figure 3e). Even so, attributed to the outstanding stretchability of PUF, the fibers themselves didn’t rupture. However, the low elongation rate of PUS (111%) itself limited the availability of PUS/PEDOT/PDMS at large strains where PUS skeletons may break and cause greatly increased resistance. In general, the rearrangement and orientation of the highly stretchable PUF rendered the PUF based conductor excellent performance in adapting high-degree deformations. Furthermore, cyclical stretching was applied to the composites to study the stability of the electrical properties under repeated deformations. Figure 4a shows the resistance variation of PUF/PEDOT/PDMS at 0% and certain strains (10%, 30%, 50%) during the first 10 stretchingreleasing cycles. Thanks for the superior resilience of PDMS, the 3D conductive composite is capable of recovering to the original shape after repeated deformations. For the 10% cyclic stretching process, the resistance variation is considerably stable. As larger stain was applied, both the resistance at releasable state and the maximal strain (30%, 50%) increased with the increasing cycles and gradually came to a stable. Nonetheless, the resistance variation is only 10% even after the 10th 50% stretching, slightly higher than the value after the 1st cycle. Figure 4b shows the resistance variation of the composite after times of stretching-releasing process. The resistance remained constant during 100 stretching cycles of 10% strain and separately increased 5%, 9% at 30% and 50% strain. Besides, the effect of the bending angle on the electrical property of the PUF/PEDOT/PDMS was investigated. Figure 4c illustrates the


10

Page 11 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


resistance as a function of the bending angle from -180° to 180°. Benefiting from the high porosity of PUF framework, the conductive network exhibited fantastic flexibility, which contributed to the outstanding electrical stability even under 180° bending. Meanwhile, the resistance stayed constant during 2000 times of 180° bending cycles. The unchanged morphology of PUF/PEDOT after the bending cycles further demonstrated the advantage of the porous fiber mat in sustaining repeated bending (Figure S8, Supporting Information). The photographs in Figure 4b and d illustrate that the brightness of the LED lamps almost remained unchanged at 50% stretching and 180° bending, which also supported the above results. The predominant bending and stretching durability endow the PUF/PEDOT/PDMS conductor huge potential in the practical use of stretchable electronics. In order to demonstrate the wide-form applications of the PUF/PEDOT/PDMS, 2*4 LED arrays were manufactured with our highly stretchable and conductive PUF/PEDOT as connections between every LED lamps. The preparation is fairly simple and convenient as illustrated in Figure 5a. First, a piece of PDMS is used as the transparent and stretchable substrate followed by placing four long pieces of PUF/PEDOT samples on PDMS in parallel with regular space. Then LED lamps were fixed on the conductive pathways and the joints were strengthened by silver paste. After encapsulated with a thin layer of PDMS on the surface, the stretchable LED arrays are obtained, which can be lit up with a relatively low voltage of 6V (Figure 5b and c). Besides, the LED arrays are capable of bearing bending and 30% stretching while remaining the conductive pathway unaffected (Figure 5d~f). The successful fabrication of our 3D conductive composite in LED arrays demonstrated its capability in the applications of large-area stretchable electronics.

CONCLUSIONS


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 23

In conclusion, we developed a novel 3D conductive network by integration of a highly stretchable PUF and conductive polymer coating, which not only possesses high conductivity but also exhibits considerable advantage in accommodating large deformations. Then PDMS was introduced to further strengthen the 3D conductive network and improve the resilience. Both of the excellent stretchability and the rearrangement and orientation of the conductive fiber networks endow the as-prepared stretchable conductor well reserved electrical performance under large deformations. As a result, the resistance only increased 20% even at a high strain of 100%. Moreover, the electrical conductivity remained constant after 2000 times of 180° bending cycles and 100 times of a 10% stretching-releasing process. The potential of the composites in the application of large-area stretchable electronics was illustrated by the fabrication of LED arrays, which can still work well under bending and 30% stretching. All the above fascinating performance provided our conductor great possibility in the preparation of the next-generation electronics.

Figure 1. Schematic illustration of PUF/PEDOT/PDMS preparation. The FE-SEM images below are (a) top view of PUF, (b) top view of PUF/PEDOT and (c) cross section of PUF/PEDOT/PDMS.


12

Page 13 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a) Stress-strain curves of 50-µm PUF and PUF-PEDOT (with 30wt% PEDOT) prepared by 50-µm PUF. (b) Electrical conductivity of PUF/PEDOT prepared by 50, 100 and 150-µm PUF as a function of the content of PEDOT. (c) Electrical-resistance variation of PUF/PEDOT/PDMS prepared by 50, 100 and 150-µm PUF as a function of tensile strain. (d) Electrical resistance variation as a function of tensile strain of representative data from previous reports:

PUS/AgNWs/PDMS;31

PUS/CuAg/PDMS;27

CuNWs

aerogel/PDMS;23

rGO-

AgNWs/PDMS28 and PUF/PEDOT/PDMS in this work.


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 23

Figure 3. (a) Photographs of the PUF/PEDOT/PDMS composite under a series of strains and the elongations are measured with a ruler. (b-e) FE-SEM images of PUF/PEDOT at (b) 0%, (c) 50%, (d) 75% and (e) 100% strain. Higher magnification SEM image of an individual fiber at 100% strain is provided in the inset of Figure e.


14

Page 15 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Electrical-resistance variation of the PUF/PEDOT/PDMS during (a) 10 and (b) 100 cycles of 10%, 30%, 50% stretching-releasing, respectively. Electrical-resistance variation of the PUF/PEDOT/PDMS as a function of (c) the bending angle and (d) the number of 180° bending. The inset photographs in (b) and (d) separately show the brightness of LED lamps depending on the strains and bends. The blue and yellow shapes represent two sides of PUF/PEDOT/PDMS.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 23

Figure 5. (a) Schematic illustration of the fabrication process of LED arrays using PUF/PEDOT/PDMS. (b) LED arrays prepared by PUF/PEDOT/PDMS and transparent PDMS substrate. (c) LED arrays are lit up at 6V. LED arrays (d) under bending, (e) at 0% strain and (f) at 30% tensile strain. The scale bars in b-f represent 5mm. Supporting Information The Supporting Information is available free of charge on the ACS Publications website. FE-SEM images of PUS, PUF/PEDOT with 60 wt% PEDOT and PUF/PEDOT after 2000 times of 180° bending; Raman Spectroscopy of PUF/PEDOT; Stress-Strain Curve of PUS as well as PUF/PEDOT prepared with different thickness; Stress-Strain cycling curves of PUF and PUF/PEDOT; electrical conductivity of PUS/PEDOT as a function of the content of PEDOT; electrical-resistance variation of PUS/PEDOT/PDMS as a function of tensile strain; electricalresistance variation of PUF/PEDOT/PDMS prepared by 50-µm PUF with 20 wt% and 40 wt% as


16

Page 17 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a function of tensile strain; R/R0 at the maximal strain of some reported 3D structured stretchable conductors. Corresponding Author *

Tel.: +86 21 64252055. Email: [email protected]; [email protected]

ACKNOWLEDGMENT Acknowledgments: This work was supported by the National Natural Science Foundation of China (91534202, 51673063), the Basic Research Program of Shanghai (15JC1401300), the Fundamental Research Funds for the Central Universities (222201718002). REFERENCES 1. Rogers, J. A.; Someya, T.; Huang, Y. Materials and Mechanics for Stretchable Electronics. Science 2010, 327, 1603−1607. 2. Hammock, M. L.; Chortos, A.; Tee. B. C.-K.; Tok, J. B.-H.; Bao, Z. The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress. Adv. Mater. 2013, 25, 5997–6038. 3. Yao, S.; Zhu, Y. Nanomaterial-Enabled Stretchable Conductors: Strategies, Materials and Devices. Adv. Mater. 2015, 27, 1480–1511. 4. Sekitani, T.; Noguchi, Y.; Hata, K.; Fukushima, T.; Aida, T.; Someya, T. A Rubberlike Stretchable Active Matrix Using Elastic Conductors. Science 2008, 321, 1468-1472. 5. Cheng, Y.; Wang, R.; Sun, J.; Gao, L. A Stretchable and Highly Sensitive Graphene-Based Fiber for Sensing Tensile Strain, Bending, and Torsion. Adv. Mater. 2015, 27, 7365–7371.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 23

6. Hwang, B.-U.; Lee, J.-H.; Trung, T. Q.; Roh, E.; Kim, D.-I.; Kim, S.-W.; Lee, N.-E. Transparent Stretchable Self-Powered Patchable Sensor Platform with Ultrasensitive Recognition of Human Activities. ACS Nano 2015, 9, 8801-8810. 7. Choi, S.; Park, J.; Hyun, W.; Kim, J.; Kim, J.; Lee, Y. B.; Song, C.; Hwang, H. J.; Kim, J. H.; Hyeon, T.; Kim, D.-H. Stretchable Heater Using Ligand-Exchanged Silver Nanowire Nanocomposite for Wearable Articular Thermotherapy. ACS Nano 2015, 9, 6626-6633. 8. Ramuz, M.; Tee, B. C.-K.; Tok, J. B.-H.; Bao, Z. Transparent, Optical, Pressure-Sensitive Artificial Skin for Large-Area Stretchable Electronics. Adv. Mater. 2012, 24, 3223–3227. 9. Yan, C.; Kang, W.; Wang, J.; Cui, M.; Wang, X.; Foo, C. Y.; Chee, K. J.; Lee, P. S. Stretchable and Wearable Electrochromic Devices. ACS Nano 2014, 8, 316−322. 10. Chen, M.; Zhang, L.; Duan, S.; Jing, S.; Jiang, H.; Luo, M.; Li, C. Highly Conductive and Flexible Polymer Composites with Improved Mechanical and Electromagnetic Interference Shielding Performances. Nanoscale 2014, 6, 3796-3809. 11. Cho, D.; Park, J.; Kim, J.; Kim, T.; Kim, J,; Park, I.; Jeon, S. Three-Dimensional Continuous Conductive Nanostructure for Highly Sensitive and Stretchable Strain Sensor. ACS Appl. Mater. Interfaces 2017, 9, 17369-17378. 12. Yan, C.; Wang, J.; Kang, W.; Cui, M.; Wang, X.; Foo, C. Y.; Chee, K. J.; Lee, P. S. Highly Stretchable Piezoresistive Graphene–Nanocellulose Nanopaper for Strain Sensors. Adv. Mater. 2014, 26, 2022–2027.


18

Page 19 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


13. Jeong, Y. R.; Park, H.; Jin, S. W.; Hong, S. Y.; Lee, S.-S.; Ha, J. S. Highly Stretchable and Sensitive Strain Sensors Using Fragmentized Graphene Foam. Adv. Funct. Mater. 2015, 25, 4228-4236. 14. Lee, P.; Ham, J.; Lee, J.; Hong, S.; Han, S.; Suh, Y. D.; Lee, S. E.; Yeo, J.; Lee, S. S.; Lee, D.; Ko, S. H. Highly Stretchable or Transparent Conductor Fabrication by a Hierarchical Multiscale Hybrid Nanocomposite. Adv. Funct. Mater. 2014, 24, 5671–5678. 15. Lee, P.; Lee, J.; Lee, H.; Yeo, J.; Hong, S.; Nam, K. H.; Lee, D.; Lee, S. S.; Ko, S. H. Highly Stretchable and Highly Conductive Metal Electrode by Very Long Metal Nanowire Percolation Network. Adv. Mater. 2012, 24, 3326–3332. 16. Park, M.; Im, J.; Shin, M.; Min, Y.; Park, J.; Cho, H.; Park, S.; Shim, M.-B.; Jeon, S.; Chung, D.-Y.; Bae, J.; Park, J.; Jeong, U.; Kim, K. Highly stretchable electric circuits from a composite material of silver nanoparticles and elastomeric fibres. Nature Nanotech. 2012, 7, 803-809. 17. Vural, M.; Behrens, A. M.; Ayyub, O. B.; Ayoub, J. J.; Kofinas, P. Sprayable Elastic Conductors Based on Block Copolymer Silver Nanoparticle Composites. ACS Nano 2015, 9, 336-344. 18. Lee, S.; Shin, S.; Lee, S.; Seo, J.; Lee, J.; Son, S.; Cho, H. J.; Algadi, H.; Al-Sayari, S.; Kim, D. E.; Lee, T. Ag Nanowire Reinforced Highly Stretchable Conductive Fibers for Wearable Electronics. Adv. Funct. Mater. 2015, 25, 3114–3121.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 23

19. Lee, Y.-H.; Kim, Y.; Lee, T.-I.; Lee, I.; Shin, J.; Lee, H. S.; Kim, T.-S.; Choi, J. W. Anomalous Stretchable Conductivity Using an Engineered Tricot Weave. ACS Nano 2015, 9, 12214-12223. 20. Chen, M.; Duan, S.; Zhang, L.; Wang, Z.; Li, C. Three-Dimensional Porous Stretchable and Conductive Polymer Composites Based on Graphene Networks Grown by Chemical Vapour Deposition and PEDOT:PSS Coating. Chem. Commun. 2015, 51, 3169−3172. 21. Khang, D.-Y.; Jiang, H.; Huang, Y.; Rogers, J. A. A Stretchable Form of Single-Crystal Silicon for High-Performance Electronics on Rubber Substrates. Science 2006, 311, 208-212. 22. Choi, W. M.; Song, J.; Khang, D.-Y.; Jiang, H.; Huang, Y. Y.; Rogers, J. A. Biaxially Stretchable “Wavy” Silicon Nanomembranes. Nano Lett. 2007, 7, 1655-1663. 23. Chen, M.; Tao, T.; Zhang, L.; Li, C. Highly Conductive and Stretchable Polymer Composites Based on Graphene/MWCNT Network. Chem. Commun. 2013, 49, 1612−1614. 24. Tang, Y.; Gong, S.; Chen, Y.; Yap, L. W.; Cheng, W. Manufacturable Conducting Rubber Ambers and Stretchable Conductors from Copper Nanowire Aerogel Monoliths. ACS Nano 2014, 8, 5707-5714. 25. Park, J.; Wang, S.; Li, M.; Ahn, C.; Hyun, J. K.; Kim, D. S.; Kim, D. K.; Rogers, J. A.; Huang, Y.; Jeon, S. Three-dimensional nanonetworks for giant stretchability in dielectrics and conductors. Nat. Commun. 2012, 3, 916. 26. Chen, M.; Zhang, L.; Duan, S.; Jing, S.; Jiang, H.; Li, C. Highly Stretchable Conductors Integrated with a Conductive Carbon Nanotube/Graphene Network and 3D Porous Poly(dimethylsiloxane). Adv. Funct. Mater. 2014, 24, 7548−7556.


20

Page 21 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


27. Duan, S.; Yang, K.; Wang, Z.; Chen, M.; Zhang, L.; Zhang, H.; Li, C. Fabrication of Highly Stretchable Conductors Based on 3D Printed Porous Poly(dimethylsiloxane) and Conductive Carbon Nanotubes/Graphene Network. ACS Appl. Mater. Interfaces 2016, 8, 2187-2192. 28. Yu, Y.; Zeng, J.; Chen, C.; Xie, Z.; Guo, R.; Liu, Z.; Zhou, X.; Yang, Y.; Zheng, Z. ThreeDimensional Compressible and Stretchable Conductive Composites. Adv. Mater. 2014, 26, 810–815. 29. Wu, C.; Fang, L.; Huang, X.; Jiang, P. Three-Dimensional Highly Conductive Graphene−Silver Nanowire Hybrid Foams for Flexible and Stretchable Conductors. ACS Appl. Mater. Interfaces 2014, 6, 21026-21034. 30. Yao, H.-B.; Ge, J.; Wang, C.-F.; Wang, X.; Hu, W.; Zheng, Z.-J.; Ni, Y.; Yu, S.-H. A Flexible and Highly Pressure-Sensitive Graphene-Polyurethane Sponge Based on Fractured Microstructure Design. Adv. Mater. 2013, 25, 6692-6698. 31. Samad, Y. A.; Li, Y.; Schiffer, A.; Alhassan, S. M.; Liao, K. Graphene Foam Developed with a Novel Two-Step Technique for Low and High Strains and Pressure-Sensing Applications. Small 2015, 11, 2380-2385. 32. Ge, J.; Yao, H.-B.; Wang, X.; Ye, Y.-D.; Wang, J.-L.; Wu, Z.-Y.; Liu, J.-W.; Fan, F.-J.; Gao, H.-L.; Zhang, C.-L.; Yu, S.-H. Stretchable Conductors Based on Silver Nanowires: Improved Performance through a Binary Network Design. Angew. Chem. Int. Ed. 2013, 52, 16541659. 33. Macdiarmid, A. G. “Synthetic metals”: A Novel Role for Organic Polymers. Curr. Appl. Phys. 2001, 1, 269-279.


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 23

34. Vosgueritchian, M.; Lipomi, D. J.; Bao, Z. Highly Conductive and Transparent PEDOT:PSS Films with a Fluorosurfactant for Stretchable and Flexible Transparent Electrodes. Adv. Funct. Mater. 2012, 22, 421–428. 35. Duan, S.; Zhang, L.; Wang, Z.; Li, C. One-Step Rod Coating of High-Performance Silver Nanowire–PEDOT:PSS Flexible Electrodes with Enhanced Adhesion after Sulfuric Acid Post-Treatment. RSC Adv. 2015, 5, 95280–95286. 36. Jin, L.; Wang, T.; Feng, Z.-Q.; Leach, M. K.; Wu, J.; Mo, S.; Jiang, Q. A Facile Approach for the Fabrication of Core–Shell PEDOT Nanofiber Mats with Superior Mechanical Properties and Biocompatibility. J. Mater. Chem. B 2013, 1, 1818–1825.


22

Page 23 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The slightly increased resistance of PUF/PEDOT/PDMS electrode derives from the arrangement and orientation of the fibers under stretching, which was proved by the unchanged lightness of the LED lamps at 0% and 100%. The successful fabrication of LED arrays with our electrodes as interconnections demonstrated their capability in the applications of large-area stretchable electronics.


Three-Dimensional Highly Stretchable Conductors from Elastic Fiber

Recommend Documents