Highly Stretchable, Transparent, and Conductive Wood Fabricated by

Subscriber access provided by UNIV AUTONOMA DE COAHUILA UADEC

Applications of Polymer, Composite, and Coating Materials

A highly stretchable, transparent and conductive wood fabricated by in-situ photopolymerization with polymerizable deep eutectic solvents Ming Wang, Ren'ai Li, Guixian Chen, Shenghui Zhou, Xiao Feng, Yian Chen, Minghui He, Detao Liu, Tao Song, and Haisong Qi ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b00728 • Publication Date (Web): 27 Mar 2019 Downloaded from http://pubs.acs.org on March 27, 2019

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 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 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.

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 41 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

A highly stretchable, transparent and conductive wood fabricated by in-situ photopolymerization with polymerizable deep eutectic solvents Ming Wang,a Renai Li,a Guixian Chen,a Shenghui Zhou,a Xiao Feng,a Yian Chen,c Minghui He*a, Detao Liua, Tao Songa and Haisong Qi*a,b

a

State Key Laboratory of Pulp and Paper Engineering, South China University of

Technology, Guangzhou 510640, China.

b

Guangdong Engineering Research Center for Green Fine Chemicals, Guangzhou

510640, China.

c Leibniz

Inst Polymerforsch Dresden eV IPF, Dresden, Germany

*Corresponding Author

Haisong Qi: [email protected]

Minghui He: [email protected]

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 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 41

KEYWORDS: transparent wood, stretchable wood, porous, deep eutectic solvent, strain/touch sensor


2

Page 3 of 41 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


ABSTRACT: The rational design of high-performance flexible transparent electrically conducting sensor attracts considerable attention. However, these designed devices predominantly utilize glass and plastic substrates, which are expensive and not environmentally friendly. Here, novel transparent and conductive woods (TCWs) were fabricated by using renewable wood substrate and low-cost conductive polymer. Polymerizable deep eutectic solvents (PDES), acrylic-acid (AA)/choline chloride (ChCl), were used as backfilling agents and in-situ photopolymerized in the delignified wood, which endowed the materials with high transparency (transmittance of 90 %), good stretchability (strain up to 80 %), and high electrical conductivity (0.16 S m-1). The retained cellulose orientation and strong interactions between cellulose-riched template and poly(PDES) render the TCWs excellent mechanical properties. Moreover, the TCWs exhibited excellent sensing behaviors to strain/ touch, even at low strain. Therefore, these materials can be used to detect weak pressure such as human being’s subtle bending-release activities. This work provides a new route to fabricate functional composite materials and devices which have promising potential for electronics applications in flexible displays, tactile skin sensors and other fields.


3


Page 4 of 41

INTRODUCTION The past few decades have seen extraordinary gain in interest for bio-based products, driven by the intensifying call of the society for petrochemical material replacement and developing materials with next-to-no environmental impact.1-3 As a wildly used sustainable and renewable material that has excellent mechanical properties, wood has various applications in daily life, including houses, furniture, artwork, heating, and decoration. Recently, wood-based materials have been increasingly considered as a bio-based template to endow a slice of novel properties. These wood-derived materials are ready to be explored for applications in new technology areas, such as electronics, biomedical devices and energy.4-11

The paramount features of wood, which can be utilized for functionalization treatments, are its sophisticated hierarchical structure and natural porous structure. It is well-known that natural wood is non-transparent due to the microsized- channels (that scatter light in the visible range) and the around 30 % content of lignin (that absorbs


4

Page 5 of 41 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


visible light) existed in the material. Moreover, the high modulus and non-stretchability of wood, which attribute to three fiber-reinforced biopolymers, namely cellulose, hemicelluloses and lignin, limit the tailored design of advanced wood-based materials with preserved structural performance.12-17 Generally, lignin as an important supporting component should be removed firstly to reduce the modulus and maintain the hierarchical structure of wood.18 After delignification, the strong interactions among cellulose, hemicelluloses, and lignin is broken, wood block turns to wood aerogel with mechanical compressibility and fragility resistance.19-20 This provided us a new probability to obtain a functional wood-based materials by

backfilling the

nano/microsized pores of delignified wood template with special polymers. For instance, transparent wood composites are achieved by backfilling with index- matching polymers. The obtained transparent wood exhibit low density (about 1.2 g cm-3), high optical transmittance (over 80 %) and haze (over 70 %), good mechanical performance.21 Interesting application areas of transparent wood include smart building,22 solar cells,23 luminescent magnetic switches24 and others.25 Obviously, the features of the resulting wood-based materials are mainly depending on the filled


5


Page 6 of 41

polymers. Until now, however, all these transparent woods reported are not stretchable, which limits their potential in applications in flexible electronics and sensors.

Herein, we developed a facile and effective approach to fabricate a novel transparent, stretchable and electrically conductive wood-based composite material. One kind of polymerizable deep eutectic solvents (PDES), acrylic-acid (AA)/choline chloride (ChCl), was chosen as backfilling agents for their low Young’s modulus and high stretchability, biodegradability, non-toxicity and renewable ability as well as their considerably low cost.26-28 In this work, the fabrication process of functional wood by PDES was introduced. Especially, it is a simple and time-saving process (UV light for seconds) to prepare poly(PDES) after infiltration in wood template by in-situ photopolymerization. The morphological, structural, mechanical, optical and electronic performance of these materials were comprehensively investigated. Moreover, their feature of conductivity is expected to render the resulting wood-based materials impressive functional properties, which would also be discussed.


6

Page 7 of 41 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


EXPERIMENTAL SECTION

Materials

Balsa wood slice (Xuhong Co. Ltd., Shanghai), sodium hydroxide, sodium sulphite, hydrogen peroxide, choline chloride (ChCl), acrylic acid (AA), poly(ethylene glycol) diacrylate (PEG(200)DA), and 2-hydroxy-4-(2- hydroxyethoxy)-2-methylpropiophenone (photoinitiator 2959, >98%, Tianjin Jiuri New Materials) were used as received.

Synthesis of PDES

The polymer used for infiltration was prepared by mixing ChCl and AA at a 1:2-1:6 molar ratio. Before being mixed, ChCl as ammonium salt was dried under vacuum at 60 oC

for 2 h, and AA as the hydrogen bond donor molecule was dried over 4 Å molecular

sieves. The mixed solution was heated with stirred at 90 oC in a closed flask for around 4 hours until a homogenous transparent liquid solution was formed. The prepared PDES was then kept in a vacuum desiccator with silica gel until further use. The initiation of polymerization reaction needs to mix the prepared PDES with crosslinkers PEG (200) DA and photoinitiator 2959 thoroughly under ultrasonication. In this work, the


7


Page 8 of 41

prepared PDES, PEG (200) DA and photoinitiator 2959 were mixed at a weight ratio of 100: 3.5: 1 with stirring for few minutes. The liquid mixtures should be kept in a dark environment or used for infiltration right after it was ready.

Fabrication of TCW

The lignin removal solution was prepared by dissolving NaOH (2.5 mol L−1) and Na2SO3 (0.4 mol L−1) in deionized water. The dried balsa wood slices (40 mm*20 mm) with different thickness were extracted in the lignin removal solution and kept boiling with stirring for 12 h, followed by rinsing in hot distilled water and acetone three times to remove most of the chemicals. The extracted wood slices were then placed in the bleaching solution (H2O2, 30%) and kept boiling until the yellow color disappeared. The colorless wood samples were washed by pure ethanol and were stored in pure ethanol. The lignin-removed wood samples were dried under vacuum for few minutes to remove solvents but maintain porous structure (Figure 1). The wood samples then were placed at the bottom of a dish and immersed in the liquid prepared PDES, which was preheated in an oven at 90 oC. After that, the lignin-removed wood template was


8

Page 9 of 41 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


infiltrated in prepolymerized PDES solution under vacuum for 5 min and repeated this vacuum infiltration process five times to ensure the full infiltration. The polymerization process was completed by passing through of the UV light source (RW-UVA-F200U, Shenzhen Runwing Company, China) with a major wavelength of 365 nm for seconds. The poly(PDES) infiltrated wood sample was peeled off from the glass slides after the poly(PDES) was completely solidified.

Characterization

The content of lignin (Klason lignin) in wood samples was determined according to TAPPI method. The surface area and micro-meso pore size of wood samples were characterized by the Brunauer−Emmett−Teller (BET) nitrogen desorption (ASAP2460), delignified wood templates were dried by supercritical drying in vacuum before. The macro-pores were measured by using a Mercury porosimetry (Micro-metrics Auto Pore 9510, USA). The morphologies of wood slices were characterized by a scanning electron microscope (SEM, EVO 18 Germany).


9


Page 10 of 41

X-ray scattering was conducted at LIX beamline (ID-16) of the National synchrotron Light Source INSLS-II) located in Brookhaven National Lab and data were collected on three detectors to cover a q-range from 3 to 0.005 A-1. Twenty individual 2-s exposure were performed for the conductive transparent wood (with thickness of 0.35 mm and 0.9 mm). The confocal images of wood/poly(PDES) were obtained using a laser scanning confocal microscope (Leica, TCS SP5 II, Germany) with the excitation wavelength of 532 nm. Rhodamine B was dissolved inside the inks to enable it show red fluorescence when exposed to the laser irradiation, poly(PDES) represented by red fluorescence, appeared inside pores of cross-linked wood cellulose channels. Fourier transform infrared (ATR-FTIR) spectra were recorded on a Bruker Vertex 70(Bruker, Germany) spectrometer.

The transmittance spectrum of transparent wood samples was measured with a UV-vis Spectrometer Cary60 (Agilent, USA.) The tensile testing was performed using a tensile machine (INSTRON 5565, 500 N load cell). Each sample was cut into a strip (30 mm × 8mm) for testing. The electrical characteristics for all the stretchable transparent


10

Page 11 of 41 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


and conductive wood were recorded using a CHI660E Electrochemical workstation. Current ranging was 200 mA, and the frequency range was from 1 Hz to 1 MHz. The TCW was cut into pieces 5 mm (width) × 5 mm (length) ×1 mm (thickness) and sandwiched by copper tapes. The testing condition was at room temperature 25 oC and the humidity was 30-35 %, the voltage for the current test for strain and touch sensor is 1V. The real-time variety of resistance were recorded using a DMM7510 Digital Graphical Sampling Multimeter (Keithley Instruments USA), the output voltage of this instrument for determination of resistance is 3.6V. Optical images were taken using a Nikon Digital Sight DS-Fil camera.

RESULTS AND DISCUSSION


11


Page 12 of 41

Figure 1. Schematic to illustrate the transparent and conductive wood (TCW) composite material was fabricated by three steps: 1. delignification, 2. infiltration and 3. photopolymerization.

As the schematic illustration in Figure 1, the fabrication of transparent and conductive wood (TCW) was mainly involved three steps: (1) delignification of natural wood (NW); (2) liquid polymerizable deep eutectic solvents (PDES) infiltration; and (3) in-situ photopolymerization of (PDES). Due to its fast growth, balsa wood possesses low density, high porosity, and thin cell walls.29 Highly ordered lumina and internal porous structure that surrounded by the cell wall line along the wood growth direction. Natural wood always appears brownish color for phenolic character of lignin contained (Figure S1). After a lignin remove process and freeze-drying, delignified wood (DW) template becomes colourless, while the well-defined channels were preserved. This structure render DW good mechanical compressibility. What’s more, quite a few microscale pores were generated in the lignin rich cell wall corner during the delignification process, as comparing to Figure 2a and d. Lignin is covalently linked to hemicellulose and therefore cross-links different plant polysaccharides, conferring


12

Page 13 of 41 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


mechanical strength to the cell wall and by extension the plant as a whole. In this work, only 65 % of the lignin content was removed by reducing the time of delignification process, which could obtain a wood template with better mechanical strength. Generally, there are harmful components, such as methyl mercaptan, dimethyl sulfide, and hydrogen sulphide, generated during the industrial delignification process. In this work, the lignin was removed by cooking in NaOH and Na2SO3 solution, which avoided the generation of toxic effluents. Moreover, there are about 35 % content of lignin retained in the material, which resulting short time-consuming and fewer energy-consuming. Thus, the delignification processes used here were more environmentally friendly.


13


Page 14 of 41

Figure 2. Scanning electron microscopy (SEM) images of NW, DW and TCW: a）NW in crosssection, b) DW in radial-section, c) TCW in cross-section, d) DW in cross-section, e) TCW in radial-section, f) higher magnification image of TCW in cross-section.

As backfilling agents, the PDES was prepared via mixing acrylic acid (AA, hydrogen bond donor) and choline chloride (ChCl, acceptor). The liquid PDES, together with a small amount of photoinitiator and crosslinker, can be quickly cured when exposed to UV light for seconds. Transparent and conductive wood (TCW) was obained by filling the channels and pores of DW template with liquid PDES under vacuum. After exposed to a UV light source for several seconds, PDES was quickly solidified in wood template. The cross-sectional SEM image in Figure 2c demonstrated that PDES can indeed fully fill the lumina. High magnification SEM image (Figure 2f) further indicated that the micro and nanoscale pores between cell wall corners were also occupied by PDES. In the radial-section (Figure 2e), the TCW exhibited a more uniform microstruture than that of DW, compared to the rough surface of DW in Figure 2b. This relative homogeneous struture can dramatically decrease the light scattering, leading to the excellent transparency of the material. Thus, for the first time, trasnparent wood


14

Page 15 of 41 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


composites was prepared by using in-situ photopolymerization. It was an easier and more time-saving process than those reported.30-32

Figure 3. The porous properties and microstructure of DW, NM and TCW: a) Macropore size distributions from the mercury intrusion measurements of the NW and DW; b) Micro/mesopore size distribution calculated from BET desorption of DW; c) 3D laser scanning confocal microscope observations of poly (PDES) and wood channels; d) Attenuated total reflection infrared spectra (ATR-IR) of TCW and DW.


15


Page 16 of 41

Wood is the most abundant natural porous carbon material. This structure is of great complexity combing micro-, meso- and macro-pores. After a lignin remove process, this well-defined channels can be preserved and the DW template still kept the original physical dimension. However, the porosity of the DW was also improved during this process. On one hand, a large number of macro-pores (10 μm ~ 60 μm in diameter) were produced in DW, as revealed by the results from mercury porosimetry (Figure 3a); on the other hand, pore size distribution based on BET desorption is indicative of the generation of much more nanopores (such as 1.9 ~ 5.0nm in pore width) due to delignification (Figure 3b). It may be result from the removal of lignin and the collapse or shrinking of cell wall. According to the results from BET tests, the surface area of the wood was increased from 1.2 m2/g to 13.2 m2/g after the delignification. This welldeveloped porous structure was beneficial for the following polymer infiltration.

Figure 3c showed the 3D laser scanning confocal microscope (LSCM) image of TCW in radial section. Liquid PDES was colored in red by mixing a little amount of Rhodamine B (λex = 590 nm). Since the wood channels themselves showed little


16

Page 17 of 41 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


fluorescence and thus represented by black wires, poly(PDES) in red fluorescence can be clearly distinguished. It can be observed that poly(PDES) was fully permeated and distributed in luminas and pores of the delignified wood. Attenuated total reflection infrared spectra (ATR) of TCW and DW (the main component is cellulose) are shown in Figure 3d. The peaks at 1719 cm−1 (C=O stretching absorption) attributed to part from AA component, which reveals that this component exists in its acidic form rather than in a molten salt. It can be noted that the absorption bands at 3371 cm−1 change to broader bands, which suggests that the molecule contains a lot of highly associated -OH. This maybe result from the forming of more hydrogen bonds between ChCl and AA, as well as strong interactions between cellulose-riched template and poly(PDES). Meanwhile, the C-N bending bond at 1244 cm−1 and sp3 hybridized C–H bond stretching peak at 2951 cm−1 attributed to part from ChCl.


17


Page 18 of 41

Figure 4. Small/wide angle X-ray scattering of TCW: a) 2D SAXS Pattern of the conductive transparent wood (TCW) in thickness of 0.35 mm; b) 1D scattering profiles extracted from the isotropic and anisotropic scattering as marked in a; c) the wide angle X-ray diffraction of TCW; d) Azimuthal angle distribution averaged between 0.05 and 0.25 A-1.

To further reveal the cellulose orientation in TCW, small/wide angle X-ray scattering of this material was investigated (Figure 4). The anisotropic component in the equatorial direction can be directly visualized in the 2D SAXS pattern (Figure 4a) and from the


18

Page 19 of 41 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


extracted 1D profile (Figure 4b). Concomitantly, a feature peak in WAXS around 1.6 A-1 can be assigned to the 200 plane of cellulose (Figure 4c). Both the streak in low q and the diffraction peak typically stem from the well orientated cellulose microfibril in the plant cell wall of wood. Similar to the raw balsa and delignificed wood, the azimuthal angle shows a narrow distribution (Figure 4d), confirming that the orientation of cellulose microfibril is well preserved within the TCW.33-34

Figure 5. Optical and mechanical properties of TCWs: a) Digital image of TCW attached to a pattern; b) UV spectrum of the NW, TCW for transverse and longitudinal direction, TCW for different thickness; c) Transverse bending and longitudinal bending of TCW; d) Stress-strain curves of NW, DW, TCW and poly(PDES); e) Young’s modulus of NW,


19


Page 20 of 41

DW, TCW and poly(PDES); f) Stress-strain curves of TCW sample at a fixed strain of 40% for 30 cycles. As the main polymer monomer, acrylic acid has a refractive index of 1.43, which is close to that of cellulose (1.47). Therefore, light scattering and light absorption were reduced in TCW, resulting in an almost complete light transmission. As shown in Figure 5a, the clear appearance of the pattern beneath the samples illustrated the high transmittance of TCW. The optical transmittance of NW, DW and TCW in different thickness were measured as showed in Figure 5b (The schematic illustrations of transverse and longitudinal positioned TCW was shown in Figure S2.). Overall, the transparency of TCWs increases with the decrease of the thickness of them. For example, TCW with a thickness of 0.35 mm exhibited nearly 90% in transparency ranging from 200 to 800 nm. It should be noted that the thickness of the present TCW samples is much larger (more than 20 times) than that of transparent nanocellulose paper reported,35-37 whereas the transmittance is comparable (Figure S1). As revealed by the results from Figure 5b, longitudinal TCW (L-TCW) showed higher transmittance then transverse TCW (T-TCW). The difference between L-TCW and T-TCW may be


20

Page 21 of 41 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


caused by light blocking of the slightly curved channels. Furthermore, TCW showed fantastic flexibility compared to natual wood. As shown in Figure 5c, TCW sample was bended horizontally and vertically in contact with a paper. There was no crack even if TCW slices were bended repeatedly. Even a high bending angle shown in Figure S3 will not trigger cracks. These results further demonstrated the TCW possesses excellent transparency and flexibility.

The mechanical strength of NW, DW, TCW and poly(PDES) were investigated by using tensile testing. Wood samples were stretched perpendicular to the direction of wood cellulose growth (shown in Figure S4a). The tensile stress of poly(PDES) is about 0.18 MPa, which has no obvious improvement by optimizing the proposition of the photoinitiator and cross-linker.38 As shown in Figure 5d, the stress of TCW was up to 1.34 MPa. Thus poly(PDES) were enhanced obviously by integrating with wood substrate. It should be noted that TCW turned to stretchable, while NW slice and other reported transparent wood was non-stretchable (Figure 5d). The corresponding Young’s modulus values of TCW slice was calculated to decreased from 30.2 MPa (NW) to


21


Page 22 of 41

2.08MPa (TCW) after PDES infiltration (Figure 5e). These features make our TCW deformable easily. As showed in Figure 5f, furthermore, TCW slices can withstand 30 or more cycles of stretch at a strain of 40 %, remaining 105-110 % of original length and 75-90 % of stress. Smaller cyclic strain at 30 % showed a better resilience (Figure S4b). Therefore, our TCW possessed not only excellent optical transmittance, but also perfect stretchability. Their favourable mechanical properties are mainly caused by: (1) the orientation of cellulose microfibril is well preserved (Figure 4a-d), and (2) the favorable interaction (hydrogen bonding) between cellulose nanofibers and poly(PDES).


22

Page 23 of 41 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 6. Electrical properties and strain/touch sensing behaviours of TCWs: a) Digital photograph of TCW with a lighting LED; b) Electrochemical impedance spectroscopy (EIS) plots of TCW with a ChCl:AA molar ratio at 1:2; c) Dependence of TCWs’ conductivity on the molar ratio of ChCl:AA in poly(PDES); d) Strain (red) and resistance changes (black) as a function of time; e) The resistance of TCW in different strain (10 % and 15 %) as a function of time; f) The current of TCW under a pressure range from 60 kPa to 120 kPa (2-3 cycles per pressure) as a function of time.

Since ChCl was involved, our TCWs also exhibit feature of electrical conductivity. When placed in an external electrical field, the positive/negative ions of ChCl parts could freely move, yielding a remarkable electrical capacity of TCW. Figure 6a shows a digital photograph of TCW slice in series with an LED. The TCW slice can display clearly the “transparent” below and make the LED glow, indicating its transparent and conductive properties. Since the poly(PDES) are ionic conductors, electrochemical impedance spectroscopy (EIS) was used to measure the conductivity of these samples, as shown in Figure 6b. The sample was cut into pieces 5 mm (width) × 5 mm (length) and sandwiched by copper tapes (Figure S5). Three different piece of TCWs showed subtle differences in Ac impedance spectroscopy owing to different amount of PDES infiltration (Figure 6b). One piece of TCW was measured along the landscape direction


23


Page 24 of 41

and transverse direction, as showed in Figure S6, EIS of two directions were almost identical, which suggested the anisotropic property of cellulose scaffold has no effect on the electrical properties. The conductivity of TCW was calculated according to equation (1).

ρ-1 = L/(s*R)=L/(s*ZR')

(1)

Where R means the resistance of TCW sample, ρ is the resistivity of composite, L means the effective length TCW slice, s is the cross-sectional area, ZR' is the real part of impedance. As shown in Figure 6c, the conductivity of TCWs is depended on the molar ratio of ChCl to AA. The conductivity of TCWs increased from 0.035 S m−1 to 0.16 S m−1 by decreasing the molar ratio of ChCl to AA from 1:2 to 1:6.

Conductive electrode together with high optical transparency are promising in a wide range of applications, including memory devices,39 solar cells,40-41

lighting

displays,42-43 pressure sensors,44-45 artificial electronic skin46-48 and photovoltaic device.49 Here, the sensing ability of the TCW to strain/stress was investigated preliminarily. Figure 6d showed the correlation of electrical resistance changes and


24

Page 25 of 41 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


mechanical strain of TCW at a strain range from 0.18% to 33%. At an extremely low strains (≈ 0.18%), the observed electrical resistance change was very small and could be neglected. With the increasing of strain, the relative electrical resistance change (Rs) of TCW increased monotonously and linearly, almost without obvious noise. The linear correlation between fractional resistance and strain can be described as an equation following:

R/R0 =GF ×   a

(2)

where GF is the abbreviation of gauge factor and stands for strain sensitivity; and the parameter, a   × GF,  refers to the initial strain for piezoresistivity effect of the materials. The calculated GF value for TCW is 1.129, which is comparable to that of metal alloys used for conventional foil gages (0.74 - 5.1).50 Thus, the TCW has great potential to be used as strain sensor.

As Figure 6e-f shown, our TCW sample exhibited high sensitive behaviours as a strain and touch sensors. The responses of the TCW to dynamic mechanical stretching were presented in Figure S7a. The electrical current values of the TCW sample


25


Page 26 of 41

recorded upon application of a fixed strain of 10%. It can be found that the output signals generated upon on/off stretch applications are sharp, uniform, and reversible. In addition, The TCW as strain gauge also exhibited excellent repeatability in detecting a particular applied external strain (20 %) with a maximum variation of ∼17 % for 1000 cycles, as showed in Figure S8a. To quantitatively assess the stretch sensitivity and continuous effectiveness of the TCW, R-T curve under different strain of 10 % and 15 % was plotted respectively, as shown in Figure 6e. The slightly uneven baselines and peaks may be explained as a small amount of unrecoverable deformation resulting from multiple stretching. This sample was sensitive to an external strain, which might be attributed to weak hydrogen bond contact between ionic parts (ChCl) and molecular networks (AA). A tight deformation of the molecular networks could give rise to related movements of ions, yielding a great change in macroscopical resistance. It has been observed that the stretch sensor responds almost instantaneously to a mechanical stimulus.


26

Page 27 of 41 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 TCW (about 1 mm thickness) can reversibly deform with/without an external pressure. This reversibly macroscopical deformation provides diverse avenues for positive/negative ions to transport, which can be reflected by the resistance changes, as shown in Figure 7Sb. The sample was cut into pieces 10 × 10 mm2 (width × length) and sandwiched by copper tapes. A tight pressure will result in the deformation of the TCW sample, which further shorten the ionic pathway, leading to a remarkable decrease of resistance and a remarkable increase of current suddenly. It should be noted that the current decrease to the same level as that of the initial value in a very short time. This result indicates that the TCW have a good recovery for pressure sensing. Consequently, the output of the electrical single was more gentle compare to stretching. The electrical current values of the TCW piezoresistive material recorded upon application of different pressures (range from 60 kPa to 120 kPa) are outlined in Figure 6f. Cyclical pressure for 2-3 times to this touch sensor was sensitive and reversible. It should be noted that, the response time of TCW-based sensor at a pressure of 90 kPa is only 170ms (Figure S8b). As shown in Figure S9, furthermore, the amplitude of


27


Page 28 of 41

current change for TCW sensor is about 4 times more than that for poly(PDES) under a pressure of 10 kPa. So the TCW is more sensitive than poly(PDES) as touch sensor.

The sensing behaviour of TCW to temperature were also investigated. As showed in Figure S10, the resistance dropped sharply when the TCW was heated on a heating stage at 50 oC. Under a higher temperature (90 oC), furthermore, the value of the resistance dropped faster. This may be due to high temperature is beneficial to the movement of positive/negative ions, which leading to the increase of conductivity of TCW.


28

Page 29 of 41 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 7. TCWs as strain /touch sensors were used to monitor human activities. The changing resistance of the sensor, corresponding to minimal strain change of a) eye blinking, b) throat swallowing, c) knees bending, d) finger bending.

As mentioned above, these TCW materials as strain / touch sensor possess outstanding flexibility and high sensitivity. We then explore their potential application in full-range recognition of human activities. Figure 7 presents a practical use of the TCWbased sensor as a physiological sensing platform. We attached it on the muscle or joint and then sealed with the transparent tape, e.g., outside of an eye corner (insets in


29


Page 30 of 41

Figure 7a), the throat (inset in Figure 7b), the knee (inset in Figure 7c) and the finger (inset in Figure 7d) to monitor the subtle motion resulting from micro-expression. The resistance changes of the sensor to these motions (minimal strain of eye blinking and throat swallowing, larger strain of finger bending and keen bending) were precisely recorded, respectively. These results demonstrated that the sensor switched rapidly at loading and unloading, where the responses of signals are repeatable and stable for the respective motion. Moreover, the shape and amplitude of the response signals are diverse for different activities. Thus, these TCW materials can be used as high sensitive monitors for full-range recognition of human activities, due to their features of flexibility and high sensitivity.

CONCLUSIONS

Novel transparent, stretchable and electroconductive wood materials were fabricated by filling the channels and pores of delignified wood with poly(PDES) via insitu photopolymerization. It is a low-cost, efficient and non-toxicity process, which provides a new route to prepare functional wood and other composites materials. The


30

Page 31 of 41 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


combination of poly(PDES) with wood matrix not only introduced high transparency (with transmittance of about 90 %) and stretchability (with strain up to 80 %) to the materials, but also led to excellent electrical conductivity (up to 0.16 S m-1). Based on their unique structure and outstanding properties, these functional woods exhibited impressive functional sensing abilities to external stimuli, especially for strain/touch. Under a wide range of stretching and pressure, the response of TCW in electrical signals were highly sensitive, well reversible and reproducible. Due to their features of flexibility and high sensitivity, the TCW-based sensor can also be used to detect human being’s subtle bending-release activities and other weak pressure. This simple and green design method for fabricating flexible and transparent electrical devices directly from natural wood is expected to unlock a range of new possibilities in smart electronics, biomedical devices and other fields.

ASSOCIATED CONTENT

Supporting information

The Supporting Information is available free of charge on the ACS Publications website.


31


Page 32 of 41

Digtal photos of NW, DW and TCW; schematic to illustrate light beam through TCW in transverse and landscape direction; electrochemical impedance spectroscopy (EIS) plots of TCW along two perpendicular directions; the sensing behaviour of TCW to temperature.

NOTES

The authors declare no competing ﬁnancial interest.

ACKNOWLEGEMENTS

The authors are grateful for the financial support for this work by the National Natural Science Foundation of China (21774036), Thousand Youth Talents Plan, State Key Laboratory of Pulp and Paper Engineering (No. 2017TS01), Guangdong Province Science Foundation (2017B090903003, 2017GC010429). We also thank Dr. Lin Yang for the SAXS data collection and reduction. The LiX beamline is part of the Life Science Biomedical Technology Research resource, jointly supported by the National Institute of Health, National Institute of General Medical Sciences under Grant P41 GM111244, and by the Department of Energy Office of Biological and Environmental Research


32

Page 33 of 41 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


under Grant KP1605010, with additional support from NIH Grant S10 OD012331. NSLS-II is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.

REFERENCES

(1) Farooq, M.; Sipponen, MH.; Seppala, A.; Osterberg, M. Eco-Friendly Flame-Retardant Cellulose Nanofibril Aerogels by Incorporating Sodium Bicarbonate. Acs Appl. Mater. Interfaces 2018, 10, 27407-27415. (2) Mekonnen, T.; Mussone, P.; Khalil, H.; Bressler, D. Progress in Bio-Based Plastics and Plasticizing Modifications. J. Mater. Chem. A 2013, 1, 13379-13398. (3) Li, Y.; Zhu, H.; Shen, F.; Wan, J.; Han, X.; Dai, J.; Dai, H.; Hu, L. Highly Conductive Microfiber of Graphene Oxide Templated Carbonization of Nanofibrillated Cellulose. Adv. Funct. Mater. 2014, 24, 7366-7372. (4) Zhu, Y.; Wang, W.; Wang, Y.; Jin, Y. Effects of pH and Sulfonated Lignin on the Enzymatic Saccharification of Acid Bisulfite- and Green Liquor-Pretreated Poplar Wood. Bioresources 2015, 10, 7361-7371. (5) Zhu, M.; Jia, C.; Wang, Y.; Fang, Z.; Dai, J.; Xu, L.; Huang, D.; Wu, J.; Li, Y.; Song, J.; Yao, Y.; Hitz, E.; Wang, Y.; Hu, L. Isotropic Paper Directly from Anisotropic Wood: Top-Down Green Transparent Substrate Toward Biodegradable Electronics. Acs Appl. Mater. Interfaces 2018, 10, 28566-28571.


33


Page 34 of 41

(6) Lee, SH.; Doherty, TV.; Linhardt, RJ.; Dordick, JS. Ionic Liquid-Mediated Selective Extraction of Lignin from Wood Leading to Enhanced Enzymatic Cellulose Hydrolysis. Biotechnol. Bioeng. 2009, 102, 1368-1376. (7) Eichhorn, SJ.; Baillie, CA.; Zafeiropoulos, N.; Mwaikambo, LY.; Ansell, MP.; Dufresne, A.; Entwistle, KM.; Herrera-Franco, PJ.; Escamilla, GC.; Groom, L.; Hughes, M.; Hill, C.; Rials, TG.; Wild, PM. Review: Current International Research into Cellulosic Fibres and Composites. J. Mater. Sci. 2001, 36, 2107-2131. (8) Parham R A, Gray R L. Formation and Structure of Wood [M]. 1984. (9) Donaldson, L. Cellulose Microfibril Aggregates and their Size Variation with Cell Wall Type. Wood Sci. Technol. 2007, 41, 443-460. (10)Kong, W, Wang, C, Jia, C, Kuang, Y, Pastel, G, Chen, C, Chen, G, He, S, Huang, H, Zhang, J, Wang, S, Hu, L, Muscle-Inspired Highly Anisotropic, Strong, Ion-Conductive Hydrogels. Adv. Mater. 2018, 30 180193439. (11)Guo, H, Buchel, M, Li, X, Wackerlin, A, Chen, Q, Burgert, I, Dictating Anisotropic Electric Conductivity of a Transparent Copper Nanowire Coating by the Surface Structure of Wood. J. R. Soc. Interface 2018, 15 20170864142. (12)Zhu, H.; Luo, W.; Ciesielski, PN.; Fang, Z.; Zhu, JY.; Henriksson, G.; Himmel, ME.; Hu, L. Wood-Derived Materials for Green Electronics, Biological Devices, and Energy Applications (Vol 116, Pg 9305, 2016). Chem. Rev. 2016, 116, 12650-12650. (13)Yan, W.; Perez, S.; Sheng, K. Upgrading Fuel Quality of Moso Bamboo Via Low Temperature Thermochemical Treatments: Dry Torrefaction and Hydrothermal Carbonization. Fuel 2017, 196, 473-480.


34

Page 35 of 41 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


(14)Jia, C.; Li, T.; Chen, C.; Dai, J.; Kierzewski, IM.; Song, J.; Li, Y.; Yang, C.; Wang, C.; Hu, L. Scalable, Anisotropic Transparent Paper Directly from Wood for Light Management in Solar Cells. Nano. Energy 2017, 36, 366-373. (15)Chen, W.; Yu, H.; Liu, Y.; Chen, P.; Zhang, M.; Hai, Y. Individualization of Cellulose Nanofibers from Wood Using High-Intensity Ultrasonication Combined with Chemical Pretreatments. Carbohyd. Polym. 2011, 83, 1804-1811. (16)Olsson, RT.; Samir, MASA.; Salazar-Alvarez, G.; Belova, L.; Strom, V.; Berglund, LA.; Ikkala, O.; Nogues, J.; Gedde, UW. Making Flexible Magnetic Aerogels and Stiff Magnetic Nanopaper Using Cellulose Nanofibrils as Templates. Nat. Nanotechnol. 2010, 5, 584-588. (17)Speck, T.; Burgert, I. Plant Stems: Functional Design and Mechanics. In Annual Review of Materials Research, D. R. Clarke and P. Fratzl, ''Eds.' 2011; 'Chapter' Annual Review of Materials Research, Vol. 41, pp 169-193. (18)Yu, J.; Paterson, N.; Blamey, J.; Millan, M. Cellulose, Xylan and Lignin Interactions During Pyrolysis of Lignocellulosic Biomass. Fuel 2017, 191, 140-149. (19)Burgert, I.; Cabane, E.; Zollfrank, C.; Berglund, L. Bio-Inspired Functional WoodBased Materials - Hybrids and Replicates. Int. Mater. Rev. 2015, 60, 431-450. (20)Song, J.; Chen, C.; Yang, Z.; Kuang, Y.; Li, T.; Li, Y.; Huang, H.; Kierzewski, I.; Liu, B.; He, S.; Gao, T.; Yuruker, SU.; Gong, A.; Yang, B.; Hu, L. Highly Compressible, Anisotropic Aerogel with Aligned Cellulose Nanofibers. Acs. Nano. 2018, 12, 140-147. (21)Wang, X.; Zhan, T.; Liu, Y.; Shi, J.; Pan, B.; Zhang, Y.; Cai, L.; Shi, SQ. Large-Size Transparent Wood for Energy-Saving Building Applications. Chemsuschem 2018, 11, 4086-4093.


35


Page 36 of 41

(22)Li, Y, Yang, X, Fu, Q, Rojas, R, Yan, M, Berglund, L, Towards Centimeter Thick Transparent Wood through Interface Manipulation. J. Mater. Chem. A 2018, 6, 10941101. (23)Jia, C.; Li, T.; Chen, C.; Dai, J.; Kierzewski, IM.; Song, J.; Li, Y.; Yang, C.; Wang, C.; Hu, L. Scalable, Anisotropic Transparent Paper Directly from Wood for Light Management in Solar Cells. Nano. Energy 2017, 36, 366-373. (24)Leung, K.; He, B.; Yang, C.; Leung, C.; Wang, HD.; Ma, D. Development of an Aptamer-Based Sensing Platform for Metal Ions, Proteins, and Small Molecules through Terminal Deoxynucleotidyl Transferase Induced G-Quadruplex Formation. Acs Appl. Mater. Interface 2015, 7, 24046-24052. (25)Guo, H.; Klose, D.; Hou, Y.; Jeschke, G.; Burgert, I. Highly Efficient UV Protection of the Biomaterial Wood by a Transparent TiO2/Ce Xerogel. Acs Appl. Mater. Interfaces 2017, 9, 39040-39047. (26)Stefanovic, R.; Ludwig, M.; Webber, GB.; Atkin, R.; Page, AJ. Nanostructure, Hydrogen Bonding and Rheology in Choline Chloride Deep Eutectic Solvents as a Function of the Hydrogen Bond Donor. Phys. Chem. Chem. Phys 2017, 19, 3297-3306. (27)Clarke, CJ.; Tu, WC.; Levers, O.; Brohl, A.; Hallett, JP. Green and Sustainable Solvents in Chemical Processes. Chem. Rev. 2018, 118, 747-800. (28)Zhang, S.; Dokko, K.; Watanabe, M. Carbon Materialization of Ionic Liquids: From Solvents to Materials. Mater. Horiz. 2015, 2, 168-197. (29)Li, Y.; Fu, Q.; Yu, S.; Yan, M.; Berglund, L. Optically Transparent Wood from a Nanoporous Cellulosic Template: Combining Functional and Structural Performance. Biomacromolecules 2016, 17, 1358-1364.


36

Page 37 of 41 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


(30)Fang, Z.; Zhu, H.; Yuan, Y.; Ha, D.; Zhu, S.; Preston, C.; Chen, Q.; Li, Y.; Han, X.; Lee, S.; Chen, G.; Li, T.; Munday, J.; Huang, J.; Hu, L. Novel Nanostructured Paper with Ultrahigh Transparency and Ultrahigh Haze for Solar Cells. Nano. Lett. 2014, 14, 765-773. (31)Zhu, M.; Song, J.; Li, T.; Gong, A.; Wang, Y.; Dai, J.; Yao, Y.; Luo, W.; Henderson, D.; Hu, L. Highly Anisotropic, Highly Transparent Wood Composites. Adv. Mater. 2016, 28, 5181-5187. (32)Zhu, M.; Li, T.; Davis, CS.; Yao, Y.; Dai, J.; Wang, Y.; AlQatari, F.; Gilman, JW.; Hu, L. Transparent and Haze Wood Composites for Highly Efficient Broadband Light Management in Solar Cells. Nano. Energy 2016, 26, 332-339. (33)Mittal, N.; Ansari, F.; Gowda, KV.; Brouzet, C.; Chen, P.; Larsson, PT.; Roth, SV.; Lundell, F.; Wagberg, L.; Kotov, NA.; Soderberg, LD. Multiscale Control of Nanocellulose Assembly: Transferring Remarkable Nanoscale Fibril Mechanics to Macroscale Fibers. Acs. Nano. 2018, 12, 6378-6388. (34)Chen, P.; Ogawa, Y.; Nishiyama, Y.; Ismail, AE.; Mazeau, K. I Alpha to I Beta Mechano-Conversion and Amorphization in Native Cellulose Simulated by Crystal Bending. Cellulose 2018, 25, 4345-4355. (35)Fang, Z.; Zhu, H.; Yuan, Y.; Ha, D.; Zhu, S.; Preston, C.; Chen, Q.; Li, Y.; Han, X.; Lee, S.; Chen, G.; Li, T.; Munday, J.; Huang, J.; Hu, L. Novel Nanostructured Paper with Ultrahigh Transparency and Ultrahigh Haze for Solar Cells. Nano. Lett. 2014, 14, 765-773.


37


Page 38 of 41

(36)Zhong, J.; Zhu, H.; Zhong, Q.; Dai, J.; Li, W.; Jang, S.; Yao, Y.; Henderson, D.; Hu, Q.; Hu, L.; Zhou, J. Self-Powered Human-Interactive Transparent Nanopaper Systems. Acs. Nano. 2015, 9, 7399-7406. (37)Yu, Y.; Yan, C.; Zheng, Z. Polymer-Assisted Metal Deposition (PAMD): A FullSolution Strategy for Flexible, Stretchable, Compressible, and Wearable Metal Conductors. Adv. Mater. 2014, 26, 5508-5516. (38)Li, R.; Chen, G.; He, M.; Tian, J.; Su, B. Patternable Transparent and Conductive Elastomers Towards Flexible Tactile/Strain Sensors. J. Mater. Chem. C 2017, 5, 84758481. (39)Shin, YJ.; Kim, RH.; Jung, HJ.; Kang, SJ.; Park, YJ.; Bae, I.; Park, C. Compression of Cross-Linked Poly(vinylidene Fluoride-Co-Trifluoro Ethylene) Films for Facile Ferroelectric Polarization. Acs Appl. Mater. Interface 2011, 3, 4736-4743. (40)Zheng Z.; Zhang S.; Zhang J.; Qin Y.; Li, W.; Yu, R.; Wei, Z.; Hou, J. Over 11% Efficiency in Tandem Polymer Solar Cells Featured by a Low-Band-Gap Polymer with Fine-Tuned Properties. Adv. Mater. 2016, 28, 5133-5138. (41)Strassel, K.; Kaiser, A.; Jenatsch, S.; Veron, AC.; Anantharaman, SB.; Hack, E.; Diethelm, M.; Nuesch, F.; Aderne, R.; Legnani, C.; Yakunin, S.; Cremona, M.; Hany, R. Squaraine Dye for a Visibly Transparent All-Organic Optical Upconversion Device with Sensitivity at 1000 Nm. Acs Appl. Mater. Interfaces 2018, 10, 11063-11069. (42)Zhou, H.; Xie, J.; Mai, M.; Wang, J.; Shen, X.; Wang, S.; Zhang, L.; Kisslinger, K.; Wang, H.; Zhang, J.; Li, Y.; Deng, J.; Ke, S.; Zeng, X. High-Quality AZO/Au/AZO Sandwich Film with Ultralow Optical Loss and Resistivity for Transparent Flexible Electrodes. Acs Appl. Mater. Interfaces 2018, 10, 16160-16168.


38

Page 39 of 41 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


(43)Cho, S.; Kang, S.; Pandya, A.; Shanker, R.; Khan, Z.; Lee, Y.; Park, J.; Craig, SL.; Ko, H. Large-Area Cross-Aligned Silver Nanowire Electrodes for Flexible, Transparent, and Force-Sensitive Mechanochromic Touch Screens. Acs. Nano. 2017, 11, 4346-4357. (44)Zhou, X.; Zhu, L.; Fan, L.; Deng, H.; Fu, Q. Fabrication of Highly Stretchable, Washable, Wearable, Water-Repellent Strain Sensors with Multi-Stimuli Sensing Ability. Acs Appl. Mater. Interfaces 2018, 10, 31655-31663. (45)Lim, S.; Son, D.; Kim, J.; Lee, YB.; Song, J.; Choi, S.; Lee, DJ.; Kim, JH.; Lee, M.; Hyeon, T.; Kim, D. Transparent and Stretchable Interactive Human Machine Interface Based on Patterned Graphene Heterostructures. Adv. Funct. Mater. 2015, 25, 375-383. (46)He, Z.; Chen, W.; Liang, B.; Liu, C.; Yang, L.; Lu, D.; Mo, Z.; Zhu, H.; Tang, Z.; Gui, X. Capacitive Pressure Sensor with High Sensitivity and Fast Response to Dynamic Interaction Based on Graphene and Porous Nylon Networks. Acs Appl. Mater. Interfaces 2018, 10, 12816-12823. (47)Ge J.; Sun L.; Zhang F.; Zhang Y.; Shi L.; Zhao H.; Zhu, H.; Jiang, H.; Yu, S. A Stretchable Electronic Fabric Artificial Skin with Pressure-, Lateral Strain-, and Flexion-Sensitive Properties. Adv. Mater. 2016, 28, 722-728. (48)Lipomi, DJ.; Lee, JA.; Vosgueritchian, M.; Tee, BCK.; Bolander, JA.; Bao, Z. Electronic Properties of Transparent Conductive Films of PEDOT:PSS on Stretchable Substrates. Chem. Mater. 2012, 24, 373-382. (49)De Arco, LG.; Zhang, Y.; Schlenker, CW.; Ryu, K.; Thompson, ME.; Zhou, C. Continuous, Highly Flexible, and Transparent Graphene Films by Chemical Vapor Deposition for Organic Photovoltaics. Acs. Nano. 2010, 4, 2865-2873.


39


Page 40 of 41

(50)Park, M, Kim, H, Youngblood, JP, Strain-Dependent Electrical Resistance of MultiWalled Carbon Nanotube/Polymer Composite Films. Nanotechnology 2008, 19 0557055.


40

Page 41 of 41 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


TOC


41

Highly Stretchable, Transparent, and Conductive Wood Fabricated by

Recommend Documents