Highly Stretchable Multifunctional Wearable Devices Based on

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Highly Stretchable Multifunctional Wearable Devices Based on Conductive Cotton and Wool Fabrics Hamid Souri, and Debes Bhattacharyya ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b04775 • Publication Date (Web): 29 May 2018 Downloaded from http://pubs.acs.org on May 29, 2018

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ACS Applied Materials & Interfaces

Highly Stretchable Multifunctional Wearable Devices Based on Conductive Cotton and Wool Fabrics Hamid Souri1*and Debes Bhattacharyya1

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Centre for Advanced Composite Materials, Department of Mechanical Engineering, The University of Auckland, Auckland, New Zealand, 1142.

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Abstract: The demand for stretchable, flexible, and wearable multifunctional devices based

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on conductive nanomaterials is rapidly increasing considering their interesting applications

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including human motion detection, robotics, and human-machine interface. There still exists

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a great challenge to manufacture stretchable, flexible, and wearable devices through a

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scalable and cost-effective fabrication method. Herein, we report a simple method for the

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mass production of electrically conductive textiles, made of cotton and wool, by

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hybridization of graphene nanoplatelets (GNPs) and carbon black (CB) particles. Conductive

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textiles incorporated into a highly elastic elastomer are utilized as highly stretchable and

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wearable strain sensors and heaters. The electromechanical characterizations of our

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multifunctional devices establish their excellent performance as wearable strain sensors to

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monitor various human motion, such as finger, wrist, and knee joint movements and sound

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recognition with high durability. Furthermore, the electrothermal behavior of our devices

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shows their potential application as stretchable and wearable heaters working at maximum

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temperature of 103 °C powered with 20 V.

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Multifunctional device, wearable strain sensor, wearable heater, graphene nanoplatelets, human motion detection

Keywords:

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Introduction

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Flexible and wearable electronics, such as strain sensors,1–7 energy storage materials,8–11

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and heaters12–14, have been rapidly developing in the last decade with considerable demands

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on maintaining high level of electrical conductance during deformation. Functional materials,

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such as graphene,15–17 carbon nanotubes,18–24 and carbon black,25,26 have been well researched

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as alternatives to conventional materials, such as conductive polymers27 and metallic

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nanomaterials28–31, used in flexible electronics. The combination of carbon nanomaterials and

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stretchable elastomers in the form of nanocomposites has been one of the favorable ways to

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fabricate flexible electronic devices.32 However, considering their poor conductivity at high

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strain levels and difficulties associated with obtaining a homogenous percolation network

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within elastomers, a simple and effective fabrication method for flexible and stretchable

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electronics remains challenging.32

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Natural materials, especially textiles, have been extensively explored as active materials

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for flexible electronics in the recent years.33–37 They offer several advantages over

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conventional materials, such as they are abundant in nature, environmentally friendly, cost-

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effective and lightweight. The knitted textiles can be highly stretched mainly due to the

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existence of the winding loops in their structure that can expand in various directions.

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Nevertheless, their electrically insulating nature is a major drawback that has challenged

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researchers to come up with methods of making conductive natural materials. Pyrolysis (also

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known as the carbonization process)35–37 and various coating processes38 of carbon

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nanomaterials are among the most commonly used methods to turn natural materials into

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highly electrically conductive materials.

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Although multifunctional devices based on carbonized natural materials provide a high

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level of electrical conductivity, the complexity of the setup, high working temperature, and

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the amount of time consumed by the process are considered as the major drawbacks of the 3



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pyrolysis process. These could result in some limitations for mass production of flexible

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electronics based on natural materials. Coating methods, such as dip-coating38,39,

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electrophoretic deposition (EPD)40, and spray coating41 have been utilized to make natural

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materials conductive; however, the electrical conductivity values were not considerably high

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for these materials. Hence, a research gap exists in the development of a simple and scalable

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method for coating the carbon nanomaterials onto natural materials to dramatically enhance

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their electrical conductivity. We previously introduced a novel and simple coating technique

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utilizing an ultrasonication bath to make conductive natural fiber yarns by a hybrid system of

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graphene nanoplatelets (GNPs) and carbon black (CB) in deionized (DI) water with the

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presence of an anionic surfactant (sodium dodecylbenzenesulfonate (SDBS)). This coating

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technique provides continuous homogenous dispersions with high energy for chemical and

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mechanical bonds between the well-suspended particles and the surfaces of the natural

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fibers.42

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Herein, we follow our previously reported method of coating carbon nanomaterials onto

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the surface of natural materials.42 This method is simple, cost-effective, and scalable for mass

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production of conductive natural fiber fabrics. Therefore, sandwich structured stretchable

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multifunctional wearable devices based on conductive cotton (CC) and conductive wool

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(CW) fabrics are developed. We chose cotton and wool fabrics because they are both

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commonly used natural materials and possess good softness combined with flexibility.43–45

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To the best of our knowledge, there have been very few studies on exploiting CW fabrics as

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cost-effective natural based active materials for stretchable and wearable electronics.

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Moreover, a research gap exists in developing CW and CC based multifunctional devices that

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can simultaneously function as wearable, stretchable and sensitive strain sensors, as well as

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high-performance wearable heaters with the aid of hybridized GNPs and CB as active

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materials. In this paper, the development of multifunctional devices through a simple, cost-

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effective, and environmentally friendly process using CC and CW fabrics is presented.

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Results and discussions

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Figure 1a schemes the process of preparing the dispersion based on the hybrid of GNPs,

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CB particles and SDBS. The trimmed dog-bone shaped cotton and wool fabrics, 100 mm in

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length and 6 mm in width, were placed in a bath sonication (60 Hz) in the presence of well-

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suspended hybrid of GNPs and CB particles in DI water. Afterwards, the coating process

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started by turning on the bath sonication and setting the deposition time to 20 minutes. In this

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process, the carbon nanoparticles could be homogenously dispersed in DI water and

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deposited on the surfaces of the fibers (refer to the Experimental Section for detailed

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information). After drying, the surface resistance of each sample was measured five times

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using a two-point probe method between both ends of the sample. The surface resistance of

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the CC and CW fabrics were found to be 286.54 ± 24.23 and 232.15 ± 35.21 Ω. The

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sandwich structured multifunctional devices were fabricated, following the procedure

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exhibited in Figure 1b. First, a thin layer of cured Ecoflex as a substrate was fabricated and

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then, the dried conductive fabrics were placed on top of the substrate. Afterwards, the fresh

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mixture of Ecoflex was poured on top of the assembly in the mould to reach the final

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thickness (4 mm for strain sensors and ~2.5 mm for heaters). Finally, the multifunctional

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devices were removed from the mould after the curing process. Figures 1c–f illustrate our

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flexible and stretchable multifunctional wearable devices based on CC and CW fabrics. The

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scanning electron microscope (SEM) images from the surface of the neat fabrics and their

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single fibers are shown in Figure S1. The SEM images of the coated fabrics revealed that the

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hybrid of GNPs and CB particles could cover the surfaces of the CC fabric and its single

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fiber, as shown in Figures 1g & 1h, respectively. Covering the surfaces and its single fiber

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lead to the formation of compacted networks of conductive particles within the fabric.

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Compacted conductive networks of particles were mainly formed within the CW fabric 5



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(Figure 1i) and on its single fiber (Figure 1j). The hybrid of GNPs and CB particles firmly

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adhered to the surfaces of the conductive fabrics and their single fibers via mechanical

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interlocking and hydrogen bonding. The SEM observations clearly confirm the presence of

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closely compacted carbon nanoparticles on the surfaces and within the fibers, resulting in a

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low level of surface resistance for the fabrics coated via ultrasonication.

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The low level of electrical resistance and cost-effectiveness of the CC and CW fabrics

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make them superior materials to be sandwiched within two layers of Ecoflex as a lightweight

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and highly stretchable elastomer to develop high performance wearable strain sensors. Before

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conducting electromechanical tests, the initial resistance of the fabricated CC and CW strain

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sensors was measured using a two-point probe method. The initial resistance of the samples

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was found to be 1.95 ± 0.31 and 1.22 ± 0.15 kΩ, respectively. It can be noticed that the

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overall resistance of the CC and CW fabrics increased when they were encapsulated within

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Ecoflex layers. This could be due to the penetration of the liquid elastomer within the yarns

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of the fabrics and coatings, as demonstrated in the cross-sectional SEM images of CW and

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CC strain sensors (Figure S2).

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The performance of our strain sensors was investigated under five stretching-releasing

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cycles at the displacement rate of 3 mm.s-1. Both CC and CW strain sensors showed a noise

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free response accompanied by negligible drift for various applied strains (25, 50, 75, and

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100%), as shown in Figures 2a & b. One can clearly observe the ascending pattern of

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resistance changes of the strain sensors as the applied strain increases. The CC strain sensors

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showed relatively high resistance change at a specified applied tensile strain, indicating their

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higher sensitivity. For instance, our CC and CW strain sensors showed about 180 and 60 % of

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resistance change in response to 100% of applied tensile strain, respectively. This behavior

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can be explained as following: it can be clearly noticed from SEM observations that

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conductive particles could penetrate through the fabrics and cover the fibers (Figures 1h &

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j). Furthermore, a strong conductive network was formed on the surface of the cotton fabric

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after the coating process, while particles tended to penetrate within the wool fibers. This

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could be due to the higher porosity of the wool fabric compared to the cotton fabric (Figure

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S1). The cracks within the percolative networks of carbon particles on the top surface of CC

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fabric can be clearly observed in Figure 1g. Therefore, the initiated cracks can gradually

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propagate by increasing the applied tensile strain on the CC strain sensors, resulting in higher

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relative change of resistance for these strain sensors compared to the CW strain sensors.

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It is important to explain the resistance change pattern of our strain sensors where it can

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be separated by three various regions. In the first region, the resistance increased with the

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applied tensile strain, whereas in the second, the resistance slightly decreased, followed by a

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slight increase in the third region. Finally, the resistance of the strain sensors decreased when

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they were unloaded. Our strain sensors showed similar behavior to the recently reported

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characteristics of sensors made with conductive textiles.46,47 This phenomenon could be

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interpreted by understanding the deformation of the weft-knitted structure of our CC and CW

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fabrics under tension. Figure S3 indicates a part of the conductive weft-knitted structure

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where coated particles on the surfaces and within the fibers contact each other. Initially, the

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area of the contact points decreased as the applied tensile strain increased, resulting in an

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increment of the resistance in the first region. In this region, the growth of crack distance

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within the conducting layer on the surface of CC strain sensors under tensile strain

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additionally resulted in a larger relative resistance change compared to the CW strain sensors

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(Figure 1g). In the second region, the contact area and the force between the contact points

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were enhanced by increasing the tensile load, thereby reducing the contact resistance (Rc) and

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the overall resistance. This phenomenon may be supported by Holm’s contact theory (refer to

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the Supporting Information). With further increment in tensile strain, crack growth in the

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conductive coatings networks as well as fracture were induced in the fabric structure. Crack

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formation resulted in a resistance increase of the strain sensors before removing the load

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(third region).46,47

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The electromechanical responses of our CC and CW strain sensors at different strain

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levels with displacement rates of 5 and 10 mm.s-1 are depicted in Figure S4. The response of

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our CC strain sensors to different displacement rates at a specified tensile strain (75 %) is

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demonstrated in Figure 2c. The relative resistance change of our strain sensors exhibited

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almost constant values within the range 3-10 mm.s-1. Moreover, our CW strain sensors

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possess a similar behavior with regard to the same displacement rates (Figure 2d). The

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responses of our CC and CW strain sensors to stretching-releasing cycles up to 100 and 150%

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at various displacement rates (3-10 mm.s-1) are depicted in Figure S5. These results indicate

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that the performance of our strain sensors has no dependency on the displacement rates.

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The sensitivity of a strain sensor can be assessed by gauge factor (GF), which is defined

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as GF= 𝛥𝛥𝛥𝛥/ (𝑅𝑅0 · 𝜀𝜀), where ΔR is the electrical resistance change, R0 denotes the initial

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typical plot of resistance change versus applied tensile strain up to 150% when the

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displacement rate was set to be 3 mm.s-1. Both types of the strain sensors exhibited a

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monotonic enhancement in resistance with the increment of applied strain. The plot can be

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divided to two linear parts. The CC strain sensors showed higher resistance change, and

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therefore, higher GFs after about 125% of strain whereas the CW strain sensors remained

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almost constant. This behavior could be due to the propagation of more cracks and fracture

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points within the conducting networks on top and within CC fabric compared to the CW

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fabric. As mentioned earlier, cracks exist within the conducting layer on the top surface of the

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CC fabric (Figure 1g). The gap among the cracks gradually increases upon stretching. The

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large gap between the cracks and subsequent fracture of the cotton fabric can cause a

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dramatic increase in the relative resistance change after applying 125% of tensile strain. In

resistance before any applied strain, and ε is the value of applied strain. Figure 2e depicts a

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contrast, the percolative networks of CW strain sensors were mainly within the fibers and did

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not show a dramatic change in their resistance even at high level of tensile strain. It can be

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clearly noticed that the sensitivity of the CC strain sensors outperforms the CW ones. The

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GFs ranged within 1.67-6.05 for CC strain sensors while those of CW strain sensors were

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below 0.5. Overall, the sensitivity of our strain sensors were higher than some of the recently

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reported strain sensors (see Table S1).26,48,49

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We conducted five stretching-releasing cycles at different strain levels (25, 50, 75, and

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100 %) at the displacement rate of 3 mm.s-1 to understand the hysteresis characteristics of our

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strain sensors (Figures 2f & g). Overall, negligible hysteresis in the response of the strain

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sensors was found up to 50% of strain; however, one can notice that further hysteresis is

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appeared as the applied percentage strain increases up to 100%. This could be due to the

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hysteresis characteristics of Ecoflex. At high levels of strains (75 to 100%), the original

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resistances of both types of our strain sensors were fully recovered at the end of each cycle.

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Figure 2h depicts the response of our CW strain sensors under 1000 cycles of stretching-

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releasing up to 75% of tensile strain at the displacement rate of 15 mm.s-1. Prior to this test,

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our sample was subjected to rupture training (up to ε=200% for 5 cycles). This could result in

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fractures within the structure of the fabric and boosting the resistance change level of our CW

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strain sensors. This increased their GFs to maximum level of 4.26. Our CW strain sensors

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could display stable properties of 1000 cycles with an insignificant drop in resistance change

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profile throughout the test. The pattern of the resistance change profile remained similar

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during the test, as indicated in Figure 2h. A similar test was carried out for our CC strain

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sensors under the same conditions. There was a significant increase in the resistance change

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value leading to the GFs of 20.4 in the last cycles, as shown in Figure S6. Unlike CW strain

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sensors, CC sensors exhibited higher resistance change. This could be due to the formation of

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more cracks within the conducting layer on the top surface of the CC fabric (Figure 1g) and

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evolution of the existing fractured areas within the CC fabric after the rupture training. This

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resulted in a gradual increase of the relative resistance change for the CC strain sensors.

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Nevertheless, the CW fabrics that possess higher stiffness showed a consistent relative

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resistance profile. This indicates that there were less cracks in their structures during rupture

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training and durability testing.

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From our results, it can be summarized that our CC based strain sensors offer higher

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sensitivity and lower hysteresis compared to the CW based strain sensors. Both strain sensors

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show excellent durability and large stretchability; however, the CW strain sensors show

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higher stability in the results. Both strain sensors showed no dependency on the displacement

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rate of applied tensile strain, therefore their application in monitoring various human

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movements was investigated to analyze their performance as wearable strain sensors.

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The movements of different finger joints were monitored by both types of strain sensors

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attached on the surface of a laboratory-grade Nitrile glove on a volunteer’s finger. A piece of

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strong double-sided tape (3M) was used to make sure that they would not slide during finger

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movements (Figures S7a & b). The resistance data points were stored every 25 ms through

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the connection of a digital multimeter (DMM) to both ends of our strain sensors. The

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responses of CW and CC strain sensors to the fast bending movements of the various fingers

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are depicted in Figures 3a & c, respectively. Similar to the results of cyclic stretching-

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releasing tests, the resistance change profiles show an increase in resistance with bending

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fingers. This was followed by a slight decrease due to the drop in contact resistance (Rc)

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when the fingers were bent further. Further increment in resistance appeared when the fingers

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were fully bent before the final drop in resistance due to straightening of the fingers. A

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similar trend was observed for all related resistance change profiles in response to the fingers

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bending at a faster rate. The relative resistance changes of our CW and CC strain sensors

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under different bending angles for each finger are shown in Figures 3b & d, respectively.

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Initially, the volunteer’s finger was slightly bent (θ < 45º) and held for a few seconds,

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resulting in a slight increase in resistance of the strain sensors; afterwards, it was fully bent

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such that a further increment in the resistance profile appeared. Finally, the resistance of the

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strain sensors recovered their original values when the finger was straightened. The sensors

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were able to fully detect the large strain movements caused by bending the knee and wrist of

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the volunteer (Figures S7c & d). Figures 3e & f demonstrate the resistance change profile of

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the strain sensors similar to those of obtained for finger joint movements.

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We evaluated the sound signals recognition from a speaker by our strain sensors. For this

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test, both types of strain sensors were attached by a piece of strong double-sided tape on a

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speaker and a DMM was connected to the strain sensor to record the data. Figure S8a

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illustrates the corresponding resistance change signals generated by CW and CC strain

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sensors when a unique track was played on the computer. Both strain sensors responded

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synchronous to the sound wave of the played track and most of the characteristic peaks were

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recognized. More distinct output signals for CW strain sensors can be observed compared to

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those of CC strain sensors. This behavior could be due to the higher sensitivity of CW strain

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sensors at very low strain levels compared to those of the CC strain sensors. The response of

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both strain sensors under a low tensile strain level but at a high displacement rate (10 mm.s-1)

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was investigated. High displacement rates could induce sudden acceleration on the strain

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sensors and simulate their performance when detecting the music beats. The plots of relative

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resistance change versus applied tensile strain (up to 0.5 %) for both CC and CW strain

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sensors are shown in Figure S8b. It can be noticed that the plots for CW and CC strain

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sensors can be divided to two linear regions with GFs of 7.23 and 3.17 between 0-0.057 %,

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and 1.89 and 1.84 between 0.057-0.5%, respectively. Higher GFs for CW strain sensors

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under very low strain level (0.05%) show their ability to detect minor beats in a played music

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track with higher sensitivity, leading to higher peaks in the output signals. As our

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experiments showed, these devices detected various signals caused by movements of various

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spots on the human skin, suggesting their human-machine interface capability.

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Another interesting application of our multifunctional devices is their potential to be used

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as wearable heating elements. For this purpose of manufacturing a heater, a similar

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fabrication process to our wearable strain sensors although the thickness of the heater devices

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was reduced to ~2.5 mm. The SEM images from the cross-section of our wearable heaters

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clearly show relatively lower thickness of the heater devices compared to that of our strain

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sensors (Figures S2c & d). The initial resistance of the CW and CC wearable heaters

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between the both ends of the samples were found to be 0.52 ± 0.03 and 1.19 ± 0.04 kΩ,

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respectively. Prior to electrothermal testing, thermogravimetric analysis (TGA) for CC and

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CW fabrics was conducted to understand the decomposition temperature of the fabrics (refer

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to the Supporting Information, Figure S9).

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Figures 4a & b indicate the typical time-dependent surface temperature changes of the

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CW and CC heaters under constant input powers of 0.32, 0.72, 1.28, and 2.05 W for 10

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minutes. The plots can be divided into three phases that includes elevating temperature

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(heating process), steady-state temperature (equilibrium), and decaying temperature (cooling

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process). It can be noted that the CW and CC heaters could reach their steady-state

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temperature in less than 150 s with the highest input power of 2.05 W. It is worth noting that

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the presence of the elastomer could delay the heating stage reaching the steady-state

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temperature due to its low thermal conductivity.47 After the steady-state stage, the power

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supply was switched off, allowing the heaters to naturally cool down to the ambient

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temperature for 5 minutes. Almost similar maximum temperatures of 93.4 and 97.2 °C

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attributed to the CW and CC heaters with the applied input power of 2.05 W were obtained.

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The slight differences in the maximum temperatures of CC and CW heaters for each input

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power could be due to the slight differences in the thickness of the active materials. The

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results show that these devices are suitable for practical applications as wearable heaters.

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The cyclic electrothermal test for these heaters under similar constant applied current was

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performed for more than 10 cycles (Figures 4c & d). The initial temperature of the devices

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was set to 30 °C by running a trial cycle. The heaters were then joule heated for 30 s under an

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applied current of 50 mA, followed by natural cooling process to the initial temperature (30

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°C). The CC heaters showed a stable dynamic electrothermal behavior with the maximum

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temperature of approximately 70.5 °C at each cycle by the input power of 3 W whereas the

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CW heaters showed lower surface temperature (~40 °C) during joule heating at each cycle

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due to a lower level of input power (1.25 W). The difference in the input power is due to the

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variation in the resistance level of the heaters. The natural cooling process to the initial

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temperature took approximately 150 and 90 seconds in each cycle for CC and CW heaters,

12

respectively. The natural cooling process was mainly from the surface of Ecoflex and hence

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an almost identical cooling time for each cycle of each heater was found.

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Further investigations on these multifunctional devices were carried out to understand the

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effect of applied tensile strain on their electrothermal behavior. For this purpose, we utilized

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our highly stretchable CC and CW strain sensors with the initial resistance of 1.95 ± 0.31 and

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1.22 ± 0.15 kΩ, respectively, to stretch them on a motorized moving stage while they were

18

subjected to an input voltage of 50 V. Simultaneously, the surface temperature was monitored

19

using a thermometer. Figure 4e presents the temperature profile of a CW strain sensor under

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0, 20, and 40% of strains. It can be noticed that the maximum surfaced temperature reached

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to 91.6 °C at 0% strain; the surface temperature of the CW strain sensor increased to 100.7 °C

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by 20 % of tensile strain. Further tensile strains on the sample up to 40 % resulted in the

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maximum surface temperature of 114.6 °C. On the other hand, the temperature profile of a

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CC strain sensor showed the maximum temperature of 78.8, 80.9, 83.7, and 90.1 ºC under

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applied tensile strains of 0, 10, 30, and 50 %, respectively. Our results indicate the stable

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electrothermal characteristics of the multifunctional devices under various applied tensile

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strain with a relatively small variation, as shown in Figure 4f. In contrast to the recently

3

reported stretachable heaters,50,51 the surface temperature of our multifunctional devices was

4

elevated under applied tensile strains. The increase in temperature of our stretchable

5

multifunctional devices could be due to the resistance variations patterns under external

6

tensile load, as outlined previously. Most of the previous studies in the literature reported

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decaying temperature under applied tensile strains, whereas our multifunctional devices show

8

almost stable eletrothermal performance under large tensile strains. Overall, the

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electrothermal performance of our wearable heaters is comparable to those recently reported

10

ones (see Table S2).

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Our CW and CC heaters were also fixed onto a volunteer’s wrist to demonstrate the

12

distribution of temperature of our wearable heaters with the aid of an infrared camera (Figure

13

S10). Both heaters showed a homogenous temperature profile on their surfaces after reaching

14

a steady-state temperature. However, higher temperatures can be observed around the

15

location of electrodes due to the generated heat by the contact resistance between the

16

electrodes and heaters. Figure S11 indicates the tendency of Tmax to the increment of input

17

power. A linear trend between the Tmax and the input power values (Pin = V2/R) can be seen.

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Here, Pin is the value for the input electric power for each input voltage (V) and R

19

represents the electrical resistance between the electrodes.52 By fitting a tread-line, Tmax can

20

be well-defined with regard to the input power using Eq. (1) and (2), for CC and CW heaters,

21

respectively:

22 23

𝑃𝑃𝑖𝑖𝑖𝑖 = 35.15(𝑇𝑇𝑚𝑚𝑚𝑚𝑚𝑚 ) + 25.91

𝑃𝑃𝑖𝑖𝑖𝑖 = 34.15(𝑇𝑇𝑚𝑚𝑚𝑚𝑚𝑚 ) + 24.14

(1) (2)

24

Both heaters showed excellent electrothermal behavior working at a low range of input

25

power. Almost similar electrothermal behavior was observed by both heaters in terms of

14


Page 15 of 29 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


1

maximum steady-state surface temperature by identical input power. The absence of any

2

major variations in maximum and minimum temperatures in dynamic heating performances

3

demonstrates the high stability of the both heaters. Based on our results, we believe that our

4

multifunctional devices have great potential as stretchable and flexible heaters for wearable

5

thermal-therapy and heating element devices.

6 7

Conclusions

8

In summary, a simple, cost-effective, and scalable technique to develop highly stretchable

9

multifunctional wearable devices using electrically conductive natural materials by an

10

ultrasonication bath has been presented. Strain sensors with GFs up to 20.4 and high

11

stretchability (applied strain more than 100%) can be achieved by encapsulating CC and CW

12

fabrics between an elastomer.

13

characteristics, good sensitivity, and high durability at high strain levels. They can also detect

14

various human movements and sound waves, making them suitable for human machine

15

interactions electronics. Our stretchable heaters can reach up to 103 ºC with an applied

16

voltage of 20 V. Moreover, our wearable heaters show excellent electrothermal performance

17

under an applied tensile strain up to 50%. Considering the simple fabrication process, cost-

18

effectiveness, and environment friendliness of our multifunctional wearable devices, we

19

believe that these wearable devices can contribute to the development of industrial fields

20

related to the flexible electronics.

Our strain sensors possess stability, low hysteresis

21 22

Experimental Section

23

Preparation of materials: In this research, commercially available weft knitted cotton

24

(measured fabric thickness ~ 0.55 ± 0.05 mm, measured yarn diameter ~ 223.9 ± 27.4 µm,

25

measured fiber diameter ~ 15.1 ± 0.8 µm, area density ~ 0.22 kg/m2) and wool (measured

15



1

fabric thickness ~ 0.7 ± 0.06 mm, measured yarn diameter ~ 509.7 ± 34.1 µm, measured fiber

2

diameter ~ 49.8 ± 4.6 µm, area density ~ 0.38 kg/m2) fabrics were locally purchased as

3

products of ALSCO and Inter-weave Ltd, New Zealand, respectively. GNPs were provided

4

by EMFUTUR, Spain, with the nominal sizes of 5 nm and 5 μm in thickness and width,

5

respectively. In addition, CB, with the average particle size of 30 nm, was purchased from

6

Degussa, Germany. We used DI water as an eco-friendly and chemical-free solvent. To

7

disperse carbon nanomaterials in DI water, SDBS, as a proprietary product of Sigma-Aldrich,

8

was employed. The two components of Ecofelx (0030) were obtained from Fiberglass shop,

9

New Zealand as products of Smooth-on Inc., USA. We chose Ecoflex (0030) as a skin safe,

10

super soft, highly stretchable (εbreak = 900%), and very strong (tensile strength ~1.38 MPa)

11

elastomer with specific gravity of 1.07 g/cc, as it possesses suitable properties for fabrication

12

of multifunctional wearable devices.49

13

Fabrication process of conductive natural fabrics using ultrasonication: The hybrid of

14

GNPs/CB dispersion was prepared in accordance to our previous study.42 The schematic view

15

of the preparation of the dispersion is shown in Figure 1a. In brief, a 1wt.% hybrid system of

16

GNPs and CB (1:1 by weight) well-suspended in DI water was prepared with the

17

SDBS/hybrid of GNPs and CB ratio of 1:3. We also tried with the ratio of 2:3; however, the

18

values for sheet resistance of the conductive fabrics were higher. First, the combination of 5

19

g of GNPs and 5 g of CB were bath sonicated for 30 min in DI water (~1 l). Next, SDBS

20

(3.33 g) was added to the dispersion and stirred for 4 hr at 60 ºC. Finally, the dispersion was

21

bath sonicated for another 2 hr to obtain more homogenous dispersion. To fabricate

22

conductive fabrics, pieces of cotton and wool fabrics were trimmed in course direction into a

23

small scale dog-bone shape (Figure 1c & S3). Here, a novel coating technique using

24

ultrasonication bath (TECHSPAN S30H, 100 W, 60 Hz) was utilized for coating process of

25

pristine trimmed fabrics according to our previous study.42 The pristine cotton and wool

16


Page 16 of 29

Page 17 of 29 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


1

fabrics with the shape similar to dog bone (Figure 1b) with a planar area of 100 mm × 6 mm

2

were put into the ultrasonication bath loaded with our well-suspended hybrid of GNPs/CB

3

particles in DI water. We coated the fabrics for 20 min to obtain highly conductive fabrics.42

4

Finally, the coated fabrics were removed from the bath and placed on a piece of tissue to

5

remove the residual water and then, fully dried in an oven at 110 °C for 1 hr.

6

Fabrication of highly stretchable and flexible multifunctional devices: Figure 1b illustrates

7

the fabrication process of the proposed multifunctional wearable devices based on the CC and

8

CW fabrics. First, the two components of Ecoflex were thoroughly mixed with a ratio of 1:1

9

(by volume). Next, the mixture was poured into a mould up to 1.5 mm in thickness. For

10

curing, the mould was moved into an oven and remained at 90 ºC for 45 minutes. Following

11

cure, the conductive dog-bone shaped fabrics were attached on the upper surface of the

12

Ecoflex substrate, and then, a fresh mixture of Ecoflex was added from top of the fabrics to

13

fill the mould with the thickness of 4 mm. Finally, the prepared devices were demoulded after

14

curing under similar conditions (45 min at 90 ºC). The stretchable and flexible

15

multifunctional devices are shown in Figures 1c-f. In the case of wearable heaters, the final

16

thickness of the devices was lowered to be ~2.5 mm to reduce the level of electrical

17

resistance of the devices.

18

Characterization of the CC and CW fabrics: The study on the surface morphology of the CC

19

and CW fabrics was carried out using scanning electron microscopy (SEM) (HITACHI SU-

20

70) images. Platinum sputtering was conducted on the samples prior to the SEM analysis.

21

The surface resistance of the samples after drying was measured using a two-point probe

22

method from both ends of the samples for five times using a digital multimeter (Keithley

23

DMM 2100). All measurements were taken at the room temperature. Thermogravimetric

24

analysis (TGA) of the pristine and conductive fabrics was performed by a TA instrument

25

(Q5000 model) in a N2 atmosphere with a temperature ramp of 10 °C.min−1 up to 800 °C.

17



Page 18 of 29

1

Characterization

2

electromechanical performance of the devices was evaluated by gripping the samples on a

3

motorized moving stage to understand their sensing behavior in stretching-releasing cycles

4

(Figure S12). The displacement rates and the applied strain profiles were controllable while

5

the resistance data was stored using a digital multimeter (Keithley DMM 7510). The applied

6

cyclic tensile strains ranged from 25 to 100 % while the displacement rates were set to be 3,

7

5, 10, and 15 mm.s-1 depending on the tests. The durability tests were carried out for more

8

than 1000 stretching-releasing cycles under 75% of applied tensile strain on the same

9

motorized moving stage. Prior to the durability tests, the devices were stretched up to 200%

10

for 5 cycles so the coated fabrics were partially fractured within the elastomer, resulting in

11

higher resistance change. In addition, the electrothermal behavior of the devices was

12

characterized by applying various input voltages using a power supply (Agilent E3649A) and

13

simultaneous monitoring of the resultant temperature on the surface of the wearable heaters

14

using a thermometer (CENTER 309 data logger thermometer). An infrared camera (FLUKE

15

Ti20) was used to observe the temperature over the surface of the devices. Moreover, the

16

changes in temperature at a constant applied voltage (50 V using Agilent E3649A) between

17

the both ends of the strain sensors (thickness of the samples = 4 mm) was monitored by using

18

a thermometer while various strains were applied on the strain sensors by the motorized

19

moving stage. All measurements were taken at room temperature.

of

our

stretchable and

wearable multifunctional

20 21 22 23 24 25 26 27 28

18


devices:

The

Page 19 of 29 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

1


ASSOCIATED CONTENT

2

TGA results, electromechanical responses of our multifunctional devices, SEM images

3

from cross section of our multifunctional devices, photographs of our multifunctional devices

4

detecting various human motion and sound detection, photographs captured by an IR camera

5

from our wearable heaters, and additional data related to the electrothermal performance of

6

our multifunctional devices. This material is available free of charge via the Internet at

7

http://pubs.acs.org.

8

AUTHOR INFORMATION

9

Corresponding Author

10

*Hamid Souri; E-mail: [email protected]; phone: +64-27-445 9880

11

Present Addresses

12

Centre for Advanced Composite Materials (CACM), Department of Mechanical Engineering,

13

The University of Auckland, Newmarket, Auckland, New Zealand, 1142.

14

Author Contributions H.S. and D.B. proposed, planned, and supervised the research. H.S.

15

performed the experiments and worked on the data analysis. H.S. and D.B. wrote the

16

manuscript.

17

Notes The authors declare no competing financial interest.

18

ACKNOWLEDGMENTS

19

The authors thank Associate Professor K.C. AW, Dr. Tim Giffney, and Dr. Mahtab Assadian

20

for providing the motorized moving stage, Mr. Morteza Amjadi and Mr. Ryan Calder for

21

their helpful comments, Dr.Velram Balaji Mohan for providing carbon nanomaterials, Dr.

22

Nam Kim for providing wool fabrics, and all other staff and technicians at the Centre for

23

Advanced Composites Materials (CACM) for their assistance. In addition, the authors would

24

like to acknowledge the Ministry of Business, Innovation & Employment, New Zealand for 19



1

their financial support (grant number: UOAX1415).

2

References:

3

(1)

Page 20 of 29

Amjadi, M.; Pichitpajongkit, A.; Lee, S.; Ryu, S.; Park, I. Highly Stretchable and

4

Sensitive Strain Sensor Based on Silver Nanowire-Elastomer Nanocomposite. ACS

5

Nano 2014, 8, 5154–5163.

6

(2)

Lee, S.; Shin, S.; Lee, S.; Seo, J.; Lee, J.; Son, S.; Cho, H. J.; Algadi, H.; Al-Sayari, S.;

7

Kim, D. E.; Lee, T. Ag Nanowire Reinforced Highly Stretchable Conductive Fibers for

8

Wearable Electronics. Adv. Funct. Mater. 2015, 25, 3114–3121.

9

(3)

10 11

Yao, S.; Zhu, Y. Wearable Multifunctional Sensors Using Printed Stretchable Conductors Made of Silver Nanowires. Nanoscale 2014, 6, 2345-2352.

(4)

Chen, S.; Wei, Y.; Yuan, X.; Lin, Y.; Liu, L. A Highly Stretchable Strain Sensor

12

Based on a Graphene/silver Nanoparticle Synergic Conductive Network and a

13

Sandwich Structure. J. Mater. Chem. C 2016, 4, 4304–4311.

14

(5)

Zhang, S.; Zhang, H.; Yao, G.; Liao, F.; Gao, M.; Huang, Z.; Li, K.; Lin, Y. Highly

15

Stretchable,

16

Nanoparticles/carbon Nanotubes Composites. J. Alloys Compd. 2015, 652, 48–54.

17

(6)

Sensitive,

and

Flexible

Strain

Sensors

Based

on

Silver

Chen, S.; Lou, Z.; Chen, D.; Jiang, K.; Shen, G. Polymer-Enhanced Highly Stretchable

18

Conductive Fiber Strain Sensor Used for Electronic Data Gloves. Adv. Mater. Technol.

19

2016, 1, 1–9.

20

(7)

Kim, S. R.; Kim, J. H.; Park, J. W. Wearable and Transparent Capacitive Strain Sensor

21

with High Sensitivity Based on Patterned Ag Nanowire Networks. ACS Appl. Mater.

22

Interfaces 2017, 9, 26407–26416.

23

(8)

Jia, D.; Yu, X.; Chen, T.; Wang, S.; Tan, H.; Liu, H.; Wang, Z. L.; Li, L. High-

24

Performance Wearable Supercapacitors Fabricated with Surface Activated Continuous

25

Filament Graphite Fibers. J. Power Sources 2017, 358, 13–21.

26

(9)

27 28

Meng, F.; Li, Q.; Zheng, L. Flexible Fiber-Shaped Supercapacitors: Design, Fabrication, and Multi-Functionalities. Energy Storage Mater. 2017, 8, 85–109.

(10)

Jost, K.; Durkin, D. P.; Haverhals, L. M.; Brown, E. K.; Langenstein, M.; De Long, H.

29

C.; Trulove, P. C.; Gogotsi, Y.; Dion, G. Natural Fiber Welded Electrode Yarns for

30

Knittable Textile Supercapacitors. Adv. Energy Mater. 2015, 5, 1–8.

31

(11)

Liu, W.; Feng, K.; Zhang, Y.; Yu, T.; Han, L.; Lui, G.; Li, M.; Chiu, G.; Fung, P.; Yu,

32

A. Hair-Based Flexible Knittable Supercapacitor with Wide Operating Voltage and

33

Ultra-High Rate Capability. Nano Energy 2017, 34, 491–499. 20


Page 21 of 29 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

1


(12)

Hong, S.; Lee, H.; Lee, J.; Kwon, J.; Han, S.; Suh, Y. D.; Cho, H.; Shin, J.; Yeo, J.;

2

Ko, S. H. Highly Stretchable and Transparent Metal Nanowire Heater for Wearable

3

Electronics Applications. Adv. Mater. 2015, 27, 4744–4751.

4

(13)

Choi, S.; Park, J.; Hyun, W.; Kim, J.; Kim, J.; Lee, Y. B.; Song, C.; Hwang, H. J.;

5

Kim, J. H.; Hyeon, T.; Kim, D. H. Stretchable Heater Using Ligand-Exchanged Silver

6

Nanowire Nanocomposite for Wearable Articular Thermotherapy. ACS Nano 2015, 9,

7

6626–6633.

8

(14)

9

Colorless Polyimide Heater for Wearable Chemical Sensors: Improved Reversible

10 11

Choi, S. J.; Kim, S. J.; Jang, J. S.; Lee, J. H.; Kim, I. D. Silver Nanowire Embedded

Reaction Kinetics of Optically Reduced Graphene Oxide. Small 2016, 12, 5826–5835. (15)

Park, J. J.; Hyun, W. J.; Mun, S. C.; Park, Y. T.; Park, O. O. Highly Stretchable and

12

Wearable Graphene Strain Sensors with Controllable Sensitivity for Human Motion

13

Monitoring. ACS Appl. Mater. Interfaces 2015, 7, 6317–6324.

14

(16)

15 16

Bae, S. H.; Lee, Y.; Sharma, B. K.; Lee, H. J.; Kim, J. H.; Ahn, J. H. Graphene-Based Transparent Strain Sensor. Carbon N. Y. 2013, 51, 236–242.

(17)

Wang, Y.; Wang, L.; Yang, T.; Li, X.; Zang, X.; Zhu, M.; Wang, K.; Wu, D.; Zhu, H.

17

Wearable and Highly Sensitive Graphene Strain Sensors for Human Motion

18

Monitoring. Adv. Funct. Mater. 2014, 24, 4666–4670.

19

(18)

Chen, K.; Gao, W.; Emaminejad, S.; Kiriya, D.; Ota, H.; Nyein, H. Y. Y.; Takei, K.;

20

Javey, A. Printed Carbon Nanotube Electronics and Sensor Systems. Adv. Mater.

21

2016, 28, 4397–4414.

22

(19)

Souri, H.; Nam, I. W.; Lee, H. K. Electrical Properties and Piezoresistive Evaluation of

23

Polyurethane-Based Composites with Carbon Nano-Materials. Compos. Sci. Technol.

24

2015, 121, 41–48.

25

(20)

Wang, Z.; Huang, Y.; Sun, J.; Huang, Y.; Hu, H.; Jiang, R.; Gai, W.; Li, G.; Zhi, C.

26

Polyurethane/Cotton/Carbon Nanotubes Core-Spun Yarn as High Reliability

27

Stretchable Strain Sensor for Human Motion Detection. ACS Appl. Mater. Interfaces

28

2016, 8, 24837–24843.

29

(21)

Souri, H.; Yu, J.; Jeon, H.; Kim, J. W.; Yang, C. M.; You, N. H.; Yang, B. J. A

30

Theoretical Study on the Piezoresistive Response of Carbon Nanotubes Embedded in

31

Polymer Nanocomposites in an Elastic Region. Carbon N. Y. 2017, 120, 427–437.

32

(22)

Cai, L.; Song, L.; Luan, P.; Zhang, Q.; Zhang, N.; Gao, Q.; Zhao, D.; Zhang, X.; Tu,

33

M.; Yang, F.; Zhou, W.; Fan, Q.; Luo, J.; Zhou, W.; Ajayan, P. M.; Xie, S. Super-

34

Stretchable, Transparent Carbon Nanotube-Based Capacitive Strain Sensors for 21



1 2

Human Motion Detection. Sci. Rep. 2013, 3, 1–9. (23)

Ryu, S.; Lee, P.; Chou, J. B.; Xu, R.; Zhao, R.; Hart, A. J.; Kim, S. G. Extremely

3

Elastic Wearable Carbon Nanotube Fiber Strain Sensor for Monitoring of Human

4

Motion. ACS Nano 2015, 9, 5929–5936.

5

(24)

Cohen, D. J.; Mitra, D.; Peterson, K.; Maharbiz, M. M. A Highly Elastic, Capacitive

6

Strain Gauge Based on Percolating Nanotube Networks. Nano Lett. 2012, 12, 1821–

7

1825.

8

(25)

9 10

Lu, N.; Lu, C.; Yang, S.; Rogers, J. Highly Sensitive Skin-Mountable Strain Gauges Based Entirely on Elastomers. Adv. Funct. Mater. 2012, 22, 4044–4050.

(26)

Kong, J. H.; Jang, N. S.; Kim, S. H.; Kim, J. M. Simple and Rapid Micropatterning of

11

Conductive Carbon Composites and Its Application to Elastic Strain Sensors. Carbon

12

N. Y. 2014, 77, 199–207.

13

(27)

Roh, E.; Hwang, B. U.; Kim, D.; Kim, B. Y.; Lee, N. E. Stretchable, Transparent,

14

Ultrasensitive, and Patchable Strain Sensor for Human-Machine Interfaces Comprising

15

a Nanohybrid of Carbon Nanotubes and Conductive Elastomers. ACS Nano 2015, 9,

16

6252–6261.

17

(28)

Gong, S.; Schwalb, W.; Wang, Y.; Chen, Y.; Tang, Y.; Si, J.; Shirinzadeh, B.; Cheng,

18

W. A Wearable and Highly Sensitive Pressure Sensor with Ultrathin Gold Nanowires.

19

Nat. Commun. 2014, 5, 1–8.

20

(29)

Jason, N. N.; Wang, S. J.; Bhanushali, S.; Cheng, W. Skin Inspired Fractal Strain

21

Sensors Using a Copper Nanowire and Graphite Microflake Hybrid Conductive

22

Network. Nanoscale 2016, 8, 16596–16605.

23

(30)

Won, Y.; Kim, A.; Yang, W.; Jeong, S.; Moon, J. A Highly Stretchable, Helical

24

Copper Nanowire Conductor Exhibiting a Stretchability of 700. NPG Asia Mater.

25

2014, 6, e132.

26

(31)

Wang, T.; Wang, R.; Cheng, Y.; Sun, J. Quasi in Situ Polymerization to Fabricate

27

Copper Nanowire-Based Stretchable Conductor and Its Applications. ACS Appl.

28

Mater. Interfaces 2016, 8, 9297–9304.

29

(32)

Amjadi, M.; Kyung, K. U.; Park, I.; Sitti, M. Stretchable, Skin-Mountable, and

30

Wearable Strain Sensors and Their Potential Applications: A Review. Adv. Funct.

31

Mater. 2016, 26, 1678–1698.

32

(33)

Ye, X.; Zhou, Q.; Jia, C.; Tang, Z.; Wan, Z.; Wu, X. A Knittable Fibriform

33

Supercapacitor Based on Natural Cotton Thread Coated with Graphene and Carbon

34

Nanoparticles. Electrochim. Acta 2016, 206, 155–164. 22


Page 22 of 29

Page 23 of 29 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

1


(34)

Huang, Y.; Hu, H.; Huang, Y.; Zhu, M.; Meng, W.; Liu, C.; Pei, Z.; Hao, C.; Wang,

2

Z.; Zhi, C. From Industrially Weavable and Knittable Highly Conductive Yarns to

3

Large Wearable Energy Storage Textiles. ACS Nano 2015, 9, 4766–4775.

4

(35)

Li, Y. Q.; Zhu, W. Bin; Yu, X. G.; Huang, P.; Fu, S. Y.; Hu, N.; Liao, K.

5

Multifunctional Wearable Device Based on Flexible and Conductive Carbon

6

Sponge/Polydimethylsiloxane Composite. ACS Appl. Mater. Interfaces 2016, 8,

7

33189–33196.

8

(36)

9

Carbonized Silk Fabric for Ultrastretchable, Highly Sensitive, and Wearable Strain

10 11

Wang, C.; Li, X.; Gao, E.; Jian, M.; Xia, K.; Wang, Q.; Xu, Z.; Ren, T.; Zhang, Y.

Sensors. Adv. Mater. 2016, 6640–6648. (37)

Zhang, M.; Wang, C.; Wang, H.; Jian, M.; Hao, X.; Zhang, Y. Carbonized Cotton

12

Fabric for High-Performance Wearable Strain Sensors. Adv. Funct. Mater. 2017, 27,

13

1604795.

14

(38)

Dong, L.; Xu, C.; Li, Y.; Huang, Z.-H.; Kang, F.; Yang, Q.-H.; Zhao, X. Flexible

15

Electrodes and Supercapacitors for Wearable Energy Storage: A Review by Category.

16

J. Mater. Chem. A 2016, 4, 4659–4685.

17

(39)

Ge, J.; Yao, H. Bin; Hu, W.; Yu, X. F.; Yan, Y. X.; Mao, L. B.; Li, H. H.; Li, S. S.;

18

Yu, S. H. Facile Dip Coating Processed graphene/MnO2nanostructured Sponges as

19

High Performance Supercapacitor Electrodes. Nano Energy 2013, 2, 505–513.

20

(40)

Souri, H.; Bhattacharyya, D. Electrical conductivity of the graphene nanoplatelets

21

coated natural and synthetic fibres using electrophoretic deposition technique. Int. J.

22

Smart Nano Mater. 2018, 1-17. DOI: 10.1080/19475411.2018.1476419.

23

(41)

Li, Y.; Chen, C.; Xu, J.; Zhang, Z.; Yuan, B.; Huang, X. Improved Mechanical

24

Properties of Carbon Nanotubes-Coated Flax Fiber Reinforced Composites. J. Mater.

25

Sci. 2015, 50, 1117–1128.

26

(42)

27 28

Souri, H.; Bhattacharyya, D. Wearable strain sensors based on electrically conductive natural fiber yarns, Mater. Des. 2018.

(43)

Wang, J.; Chen, Y.; An, J.; Xu, K.; Chen, T.; Müller-Buschbaum, P.; Zhong, Q.

29

Intelligent Textiles with Comfort Regulation and Inhibition of Bacterial Adhesion

30

Realized

31

Methacrylate) to Cotton Fabrics. ACS Appl. Mater. Interfaces 2017, 9, 13647–13656.

32

(44)

by

Cross-Linking

Poly(n-Isopropylacrylamide-Co-Ethylene

Glycol

Zhong, Q.; Chen, Y. Y.; Guan, S. L.; Fang, Q. S.; Chen, T.; Müller-Buschbaum, P.;

33

Wang, J. P. Smart Cleaning Cotton Fabrics Cross-Linked with Thermo-Responsive

34

and Flexible poly(2-(2-Methoxyethoxy)ethoxyethyl Methacrylate-Co-Ethylene Glycol 23



1 2

Methacrylate). RSC Adv. 2015, 5, 38382–38390. (45)

Yang, H.; Zhu, H.; Hendrix, M. M. R. M.; Lousberg, N. J. H. G. M.; De With, G.;

3

Esteves, A. C. C.; Xin, J. H. Temperature-Triggered Collection and Release of Water

4

from Fogs by a Sponge-like Cotton Fabric. Adv. Mater. 2013, 25, 1150–1154.

5

(46)

Wang, C.; Xia, K.; Jian, M.; Wang, H.; Zhang, M.; Zhang, Y. Carbonized Silk

6

Georgette as an Ultrasensitive Wearable Strain Sensor for Full-Range Human Activity

7

Monitoring. J. Mater. Chem. C 2017, 5, 7604–7611.

8

(47)

9

Intrinsically Stretchable and Conductive Textile by a Scalable Process for Elastic

10 11

Wang, C.; Zhang, M.; Xia, K.; Gong, X.; Wang, H.; Yin, Z.; Guan, B.; Zhang, Y.

Wearable Electronics. ACS Appl. Mater. Interfaces 2017, 9, 13331–13338. (48)

Yamada, T.; Hayamizu, Y.; Yamamoto, Y.; Yomogida, Y.; Izadi-Najafabadi, A.;

12

Futaba, D. N.; Hata, K. A Stretchable Carbon Nanotube Strain Sensor for Human-

13

Motion Detection. Nat. Nanotechnol. 2011, 6, 296–301.

14

(49)

Amjadi, M.; Yoon, Y. J.; Park, I. Ultra-Stretchable and Skin-Mountable Strain Sensors

15

Using Carbon Nanotubes-Ecoflex Nanocomposites. Nanotechnology 2015, 26,

16

375501.

17

(50)

Kang, J.; Kim, H.; Kim, K. S.; Lee, S. K.; Bae, S.; Ahn, J. H.; Kim, Y. J.; Choi, J. B.;

18

Hong, B. H. High-Performance Graphene-Based Transparent Flexible Heaters. Nano

19

Lett. 2011, 11, 5154–5158.

20

(51)

Ilanchezhiyan, P.; Zakirov, A. S.; Kumar, G. M.; Yuldashev, S. U.; Cho, H. D.; Kang,

21

T. W.; Mamadalimov, A. T. Highly Efficient CNT Functionalized Cotton Fabrics for

22

Flexible/wearable Heating Applications. RSC Adv. 2015, 5, 10697–10702.

23

(52)

Souri, H.; Yu, S. J.; Yeo, H.; Goh, M.; Hwang, J.-Y.; Kim, S. M.; Ku, B.-C.; Jeong, Y.

24

G.; You, N.-H. A Facile Method for Transparent Carbon Nanosheets Heater Based on

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Polyimide. RSC Adv. 2016, 6, 52509–52517.

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1 2

Figure 1. a) Schematic illustration of the preparation of carbon nanomaterials dispersions in

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DI water; b) schematic view of the fabrication process of the multifunctional devices; c-f)

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photographs of our flexible, stretchable and wearable multifunctional devices; g) SEM image

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related to the surface of the CC; and h) coated carbon nanoparticles coated on a single cotton

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fiber; i) SEM image related to the surface of the CW fabric; and j) coated carbon

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nanoparticles coated on a single wool fiber.

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1 2

Figure 2. Electromechanical performance of our strain sensors: a) relative changes of

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resistance versus different strains under cyclic stretching–releasing at displacement rate of 3

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mm.s-1 for CC strain sensors and b) for CW strain sensors; c) relative resistance variations

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under cyclic stretching–releasing with a strain of 75% at displacement rates of 3, 5, and 10

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mm.s-1 for our CC strain sensors, and d) for our CW strain sensors; e) the relative resistance

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changes for our strain sensors up to 150% of tensile strain; f) hysteresis curves of 5

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stretching–releasing cycles up to various tensile strains for CC strain sensors, and g) wool

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strain sensors; h) performance of our CW strain sensors under 1000 cyclic stretching–

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releasing up to 75% of tensile strain at 15 mm.s-1, indicating their stability and durability.

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Figure 3. Detection of large-strain human motion (finger movements) by our strain sensors;

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a) plots showing the response of a CW strain sensor to the fast movements of each finger’s

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joints, b) plots indicating the response of our CW strain sensors to bending-holding of each

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finger with regard to the joint degree of bending, c) plots showing the response of a CC strain

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sensor to the fast movements of each finger’s joints, d) plots indicating the response of our

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CC strain sensors to bending-holding of each finger with regard to the joint degree of

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bending, e) detection of knee joint movements by our strain sensors, and f) monitoring the

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wrist bending movements by our strain sensors.

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1 2

Figure 4. Time-dependent temperature changes of a) CW and b) CC wearable heaters under

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various input power (0.32, 0.72, 1.28, and 2.05 W); c) cyclic electrothermal performance of

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c) CW and d) CC heaters under zero tensile strain under applied current of 50 mA, showing

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the heating stability of our wearable heaters, e) elevation of the temperature of a CW strain

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sensor (resistance ~ 1.2 kΩ) under stepwise strains of 0−40% at a constant dc voltage of 50

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V, and f) elevation of the temperature of a CC strain sensor (resistance ~ 1.9 kΩ) under

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stepwise strains of 0−50% at a constant dc voltage of 50 V.

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Graphical abstract:

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Highly Stretchable Multifunctional Wearable Devices Based on

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