1 School of Chemical Engineering and Technology, Tianjin University,Tianjin 300072, China
2 School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University,Tianjin 300350, China
Bin Li, Shuang Jiang
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Received
Revised
Published Online
2020-06-01
2020-07-07
2020-11-30
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Abstract
Carbon-based materials have excellent conductivity, good stability, and low price. They are widely used in the preparation of stretchable conductive nanocomposites, and have tremendous application potential in the field of stretchable and wearable electronic devices, which has attracted lots of attention. This paper introduces the carbon-based materials, such as carbon black, carbon nanotubes and graphene. The preparation methods of these nanocomposites are also summarized, such as in-situ polymerization, melt blending and solution mixing, followed by the introduction of traditional and new printing technology. Then this paper analyzes the conductive mechanisms of composite materials including the percolation threshold, and focuses on their application in the field of stretchable sensors and stretchable energy storage devices. The shortcomings of the current research on stretchable conductive composites based on nano-carbon fillers are pointed out: poor dispersion of conductive fillers, unstable conductive network and inability to mass-produce, and the corresponding solutions are put forward. Finally, the applications of stretchable conductive composites based on nano-carbon fillers are prospected, including miniaturized, stretchable and wearable electronic devices.
Contents
1 Introduction
2 Conductive composites based on nano⁃carbon fillers
2.1 Carbon black
2.2 Carbon nanotube
2.3 Graphene
3 Preparation of stretchable conductive composites
3.1 Polymer
3.2 Preparation of conductive ink
3.3 Printing technology
4 Conduction mechanism of stretchable conductive composites based on nano⁃carbon fillers
The stretchable conductive composites based on nano-carbon filler refer to a kind of composites with carbon material as conductive filler. The key of stretchable conductive composites is whether they can maintain the conductive network under large strain and recover their original properties after releasing the strain. Generally speaking, most polymers with flexibility and elasticity have no conductivity, while carbon materials such as graphene, carbon nanotubes (CNT) and carbon black (CB) have high conductivity, but they have no deformation ability and can not be stretched[1]. Therefore, conductive nano-materials and stretchable polymers are usually mixed in a specific way to prepare stretchable conductive nanocomposites, which are applied to the fields of strain sensors, stretchable batteries, stretchable supercapacitors and wearable medical devices[2⇓⇓~5][6⇓~8][9⇓~11][12]. Compared with metal conductive fillers, carbon materials have more excellent stability and modification ability, lower price and lighter weight, so they can be produced on a large scale to meet the needs of stretchable electronic devices.
In this paper, the preparation and application of conductive and stretchable nanocomposites based on carbon nano-fillers in recent years are reviewed.The types, preparation methods and printing technologies of conductive fillers are mainly introduced.The conductive mechanism of conductive and stretchable nanocomposites is discussed, and its application in the field of stretchable electronic devices is summarized.
2 Introduction of Conductive Composites Based on Nano-carbon Filler
Carbon material is one of the most widely used materials, which has many advantages, such as good stability, low price, abundant raw material reserves and good biocompatibility, mainly including graphite, carbon fiber, carbon black, graphene, graphyne, carbon nanotubes and fullerenes (C60). Graphite is the most common carbon material, which is often used as lubricating materials, corrosion-resistant materials, refractory materials and raw materials for the preparation of graphene oxide, or processed into various shapes for conductive materials such as pen cores and electrodes. Carbon fiber is a kind of special fiber which is mainly composed of carbon element.Different fibers have different carbon content and have excellent mechanical strength and modulus along the fiber axis direction.Carbon fiber is often used as a reinforcing material to prepare composites with polymers, metals or ceramics, but generally not used to prepare stretchable conductive nanocomposites. C60 is a new type of hollow molecule composed entirely of carbon, which is currently used in the field of organic solar cells as an electron transport layer to improve the photoelectric conversion efficiency of the cell. Graphene is also a kind of all-carbon nanostructure material, but its structure is quite different from graphene, which is not conducive to electron mobility, so it has poor conductivity and can not be used to prepare conductive composites. Carbon black, graphene and carbon nanotubes (as shown in Figure 1) are nano-scale conductive materials with small size and excellent electrical properties, so they are widely used in stretchable conductive nanocomposites, which have attracted the attention of researchers and many research results, but their properties are still insufficient to meet the actual needs of production and life. Therefore, the future development trend of stretchable conductive composites must be the synergistic effect of multiple materials, the continuous development of new carbon materials, and the combination of multiple preparation processes, so as to prepare stretchable conductive nanocomposites with excellent properties.
2.1 Carbon black
Carbon black is one of the most important carbon fillers, which is widely used in various industrial production. The nanomaterial has a series of advantages, such as high specific surface area, good chemical stability, high thermal and electrical conductivity, and low cost. Carbon black is mainly produced by thermal decomposition or incomplete combustion of hydrocarbon compounds. The size, structure, and conductivity of carbon black particles vary depending on the choice of raw materials and the method of manufacture. The carbon black particles have an amorphous and quasi-graphitic structure. The average particle size of carbon black is 3 ~ 100 nm, which tends to agglomerate together to form aggregates, and these aggregates will form larger spatial network structure aggregates under the action of Van der Waals force[13]. Wen et al. Used carbon black and polydimethylsiloxane to prepare stretchable conductive composites, which had good conductivity and mechanical stability, and were used to assemble biological microchips[14]. Bhagavatheswaran et al. mixed carbon black and styrene-butadiene rubber, and added silica particles to prevent the agglomeration of carbon black, successfully prepared a conductive composite material with a conductivity of 40 S·m-1 and a maximum elongation of 200%, and realized its application in pressure sensors[15]. Kim et al. Used carbon black and carbon nanotubes mixed with polybutylene adipate/terephthalate (PBAT, commonly known as Ecoflex) to prepare a composite material, which was used as a current collector in aqueous lithium-ion batteries and could still work properly under 100% strain[6]. Fig. 2 shows the tensile conductivity of carbon black conductive nanocomposites. It can be seen that the conductivity is generally low, but the conductivity of the composites can be significantly improved by adding carbon nanotubes[6,14,15].
2.2 Carbon nanotube
In essence, carbon nanotubes are hollow cylindrical tubular structures formed by curling graphene sheets (hexagonal structures) according to a specific spiral angle. There are two types of carbon nanotubes: (1) single-walled carbon nanotubes (SWCNTs), which can be thought of as individual graphene sheets rolled into a cylinder; (2) Multi-walled carbon nanotubes (MWCNTs), which can be seen as a stack of multiple concentric layers of graphene. There are many methods to prepare carbon nanotubes, such as arc evaporation, laser ablation, chemical vapor deposition (CVD) and so on[16,17]. Carbon nanotubes have the properties of high modulus, high stiffness and low density. Their elastic modulus is up to 1.8 TPa, and they have excellent electrical conductivity, so they are ideal materials for the preparation of composites. Someya et al. Mixed single-walled carbon nanotubes with fluorinated rubber, resulting in composites with conductivity greater than 100 S·cm-1 and stretchability greater than 100%, and successfully constructed stretchable active matrix displays[18]. Kim et al. prepared a composite using MWCNTs obtained by chemical vapor deposition mixed with polyurethane, and almost no decrease in conductivity was observed in the composite at 10% to 20% strain[19]. Zhang et al. Used reduced graphene oxide (rGO) and carbon nanotubes as conductive fillers and styrene-butadiene rubber as polymer to prepare composites with conductivity of 3.62 S·cm-1 and stable at low tensile strain[20]. Fig. 3 shows the tensile conductivity of carbon nanotube conductive nanocomposites, which is significantly improved compared to carbon black conductive nanocomposites[6,18⇓ ~20].
2.3 Graphene
Graphene is composed of a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice, which can be deformed to obtain other carbon materials. Graphene has many excellent properties, such as high specific surface area (2630 m2·g-1), excellent thermal and chemical stability, high electrical conductivity, high electron mobility (200 000 cm2·v-1·s-1), and mechanical flexibility[21][22][23,24]. At the same time, the unique properties of graphene and its derivatives, such as graphene oxide (GO) and rGO, make them the basis for the construction of self-supporting graphene composites and endow them with excellent electrical, mechanical and thermal properties. Kim et al. Used graphene foam and polydimethylsiloxane to prepare a stretchable graphene honeycomb structure with 72 S·m-1 conductivity, and successfully prepared a stretchable light-emitting display with the material as a circuit[25]. Cheng et al. Prepared graphene with 3D structure by chemical vapor deposition, and filled it with polydimethylsiloxane to prepare a composite material, which has excellent conductivity and can be used as a stretchable conductor in many fields[26]. Qu et al. Used graphene and polyurethane fibers to prepare stretchable conductive fibers, which can be used in strain sensors and stretchable conductors[27]. Fig. 4 is a schematic diagram of the tensile conductivity of the graphene conductive nanocomposite, but the polymer is usually used to percolate the graphene with a 3D structure, and the process is complex, which is not conducive to large-scale preparation and up[20,25⇓ ~27]
3 Preparation of stretchable conductive composites
3.1 Polymer Matrix
Although the electrical conductivity of elastic nanocomposites is largely influenced by the electrical properties of the incorporated conductive fillers, the stretchable polymer matrix plays a key role in maintaining the stability of the percolation network under large mechanical deformation[28]. In addition, the concentration and type of the conductive filler also affect the mechanical properties of the elastic composite[29]. For example, the Young's modulus generally increases with increasing conductive filler.
Polydimethylsiloxane and Ecoflex are a class of chemically crosslinked elastomers that are widely used as elastic matrices for stretchable conductive composites. The Young's modulus and the maximum elongation strain of the elastic polymer can be controlled by controlling the curing temperature and the amount of crosslinking agent[30]. The conductive filler is typically embedded in the upper skin of the elastomer or dispersed in the elastomer matrix during the crosslinking reaction of the elastomer. However, too much conductive filler can also hinder the crosslinking reaction. In contrast to chemically crosslinked elastomers, physically crosslinked elastomers do not rely on covalent bonds with polymer chains, and crosslinking occurs even in the presence of large amounts of conductive filler[31]. In addition, the elastic composite can be reshaped by dissolving in a solvent or hot pressing, and the excellent processability is favorable for preparing stretchable electronic devices with various shapes. However, the conductivity depends on the proportion of conductive fillers used in the composite, and the stiffness of the elastic conductor increases with the increase of conductive fillers. Therefore, in order to maximize electrical conductivity and optimize the mechanical properties of the composite, a trade-off must be made between electrical conductivity and stretchability.
3.2 Process for preparing conductive ink
The preparation methods of nano-carbon filler conductive ink mainly include in-situ polymerization, melt blending and solution blending, as shown in Figure 5. Whichever method is chosen, the dispersion of the conductive filler in the polymer is critical. This is because the final properties of the elastic conductive composite depend on the dispersion morphology of the conductive filler in the polymer.
3.2.1 In-situ polymerization
In-situ polymerization is often used in the preparation of conductive ink with nano-carbon filler, and the conductive filler has a high degree of dispersion in the polymer matrix. In that method, the conductive fill and the desired polymer monome are thoroughly and uniformly mixed. Initiators and heat are used to initiate the polymerization and the properties of the composite are adjusted by controlling the temperature, pressure or time. Hu et al. Prepared graphene/polystyrene composites by in-situ emulsion polymerization. The polymer monomer was adsorbed on the surface of graphene to make it fully dispersed in organic solvents. The composites prepared by this method had excellent conductivity and significantly improved the glass transition temperature of polystyrene[32]. In-situ polymerization has many advantages over other methods, such as high miscibility, uniform dispersion of carbon fillers in polymer matrix, and strong interaction between carbon fillers and polymer matrix, which ensures the controllable structure and excellent properties of composites. However, due to the generally high viscosity of polymers, the composites prepared by this method are not conducive to further processing.
3.2.2 Melt blending method
Melt blending is also one of the commonly used methods. The method means that the polymer is melted and fully mixed with the conductive filler at a high temperature, and a single-screw or twin-screw extruder and an injection molding machine are commonly used equipment for melt blending. The method has the advantages of simple operation and few steps, and is beneficial to large-scale production and preparation of the conductive composite material. But at the same time, because of the high viscosity of the polymer, it is not conducive to the uniform dispersion of conductive fillers, and it often needs to add more fillers to obtain higher conductivity. Duan et al. Prepared MWCNT/styrene-butadiene-styrene block copolymer (SBS) conductive composites by melt blending, and the percolation threshold of the composites was 0.98 wt%, but the conductive network obtained by melt blending was disordered, which made it easy to break under strain[33]. Melt blending has the unique advantage of being able to directly use high temperature and shear force to graft fillers onto polymer chains without the addition of acidic chemicals and solvents, so as to synthesize a variety of polymer composites in batch production, but the limitation of this method is the poor dispersion of conductive fillers in the polymer matrix during mechanical mixing.
3.2.3 Solution Mixing Method
Solution mixing method is the most commonly used method to prepare conductive ink with nano-carbon filler, which requires little energy consumption and does not require complex equipment. Generally, the method first mixes the conductive filler and the polymer matrix in a suitable organic solvent, such as N, N-dimethylformamide (DMF), and then sufficiently disperses the conductive filler in the polymer matrix by ultrasonic treatment, mechanical or magnetic stirring to obtain the conductive ink. The ink is then prepared into a stretchable conductor by various printing methods, and a surfactant can also be added to promote uniform dispersion of the conductive filler[34]. Hwang et al. modified MWCNT after acid treatment with surfactant, prepared MWCNT/polyamide 66 composite by solution blending method, and proved the uniform dispersion of MWCNT in the polymer matrix. The results showed that the electrical and mechanical properties of the composite with surfactant were improved by about 20% compared with those of the composite without surfactant[35]. This method has been widely used in the preparation of carbon conductive composites because of its easy processing, low energy consumption, and more uniform and controllable dispersion of conductive fillers in the polymer matrix. Because of the ability to disperse the carbon conductive fillers uniformly in the polymer matrix, the solution mixing method has become the most promising method to prepare the conductive composites based on nano-carbon fillers.
3.3 Printing Technology
Conductive inks often require multiple printing techniques to produce composites. In recent years, researchers have printed functional inks on elastic substrates by various printing techniques to prepare stretchable conductive composites based on nano-carbon fillers[36]. Printing technology is mainly divided into traditional printing and digital printing. Traditional printing technology is generally divided into blade coating, screen printing, screen printing, flexographic printing and spraying. Digital printing is generally divided into 3D printing and inkjet printing. The specific process is shown in Figure 6[37]. Compared with traditional microfabrication technology, printing technology is cheap, and flexible components such as current collectors and electrodes can be manufactured on a large scale according to demand.
(1) Scrape coating
Blade coating is the most common printing technique used in the mass production of stretchable electronic devices (fig. 6a). Blade coating works by placing a blade on a substrate and placing ink on one side of the blade with a distance between the blade and the substrate. The doctor blade is moved over the substrate at a speed to disperse the ink evenly, and the substrate is then placed in a drying oven or dried at room temperature. Because knife coating is a blanket coating process, it cannot be used to pattern ink on a substrate. The thickness of the film after drying depends on the concentration and viscosity of the ink. The ink with large particles tends to shrink after drying, while the ink with nanoparticles tends to form micropores during drying, which reduces the integrity of the finished product.
(2) Screen printing
Screen printing involves cutting a plastic or metal stencil as required, placing it on a substrate, using a squeegee to advance the ink over the stencil, removing the stencil when the squeegee reaches its end point, and finally transferring the pattern from the stencil to the substrate (Figure 6 B). In addition, the thickness of the coating can be changed by adjusting the concentration of the ink or the thickness of the stencil, but the concentration of the ink should not be too low to prevent bleeding from the screen edge.
(3) Spraying
The spray method allows printing on any surface using a variety of viscosity inks (Figure 6 C). Spray printing is based on a spray gun with a high velocity compressed carrier gas that atomizes and sprays the ink onto a target substrate. The thickness of the spray coating can be controlled by adjusting parameters such as nozzle size, gas pressure, ink composition, and spray times. The greatest advantage of this method is that it can be used for spray printing on various uneven surfaces, such as foam and various mesh structures. Because the spray-printed ink dries faster, different components of stretchable electronic devices can be printed in turn, greatly reducing production time.
(4) Flexographic printing
Flexography is a screen-based, high-speed printing process that uses a relief plate to transfer a pattern onto a substrate (Figure 6d). Depending on the complexity of the pattern, the final pattern can be printed in multiple steps. The standard flexographic printing process consists of four rollers: an impregnating roller, an anilox roller, a printing cylinder, and an impression roller. The thickness of the ink pattern obtained by flexographic printing is very low, and in order to increase the thickness of the image, multiple sets of printing equipment are often required to work at the same time.
(5) Screen printing
Screen-printing refers to fixing a weave, wire mesh or synthetic fiber to a support frame and forming a desired pattern in the mesh by filling the mesh with a photosensitive emulsion, then selectively crosslinking and removing the uncrosslinked portion using a solvent, with pores at the pattern allowing ink to penetrate (Figure 6 e). The ink is placed on one end of the screen, the squeegee carries the ink and moves linearly towards the other end, while the squeegee is pressed down to make the screen contact with the substrate, and the ink is transferred to the substrate after the squeegee passes through the pores. The method is widely used in industry to print text and images on fabrics, so stretchable electronic devices can be manufactured on a large scale.
(6) Inkjet printing
Inkjet printing is a form of digital printing (Figure 6 f). Using this technology, ink can be dropped onto a substrate to form the desired pattern, and a resolution of 1200 dpi (drops per inch) can be achieved, depending on the quality of the ink and the performance of the print head. Ink droplets are formed by mechanically compressing the ink through a nozzle, or by heating the ink to increase its pressure, and the thickness of the printed layer ultimately depends on the number, volume, concentration of ink droplets and the area covered by the printed layer. Inks typically require a mixture of solvents to achieve the desired properties. In order to prevent the deposition of the filler in the ink from clogging the nozzle, a surfactant is often added to the ink to increase the steric repulsion between particles to prevent agglomeration, thereby improving the dispersibility of the conductive particles in the ink. Compared to other printing technologies, inkjet printing is slow and the printed layer is relatively thin, which limits its ability to print thick stretchable electronic devices.
(7) 3D printing
The 3D printing system is mainly composed of a computer, a dispenser and an injector, which can be used to print ink with a wide range of viscosity. By adjusting the pressure output by the dispenser, the ink can be printed in the form of filaments or droplets (Figure 6G). Compared with other printing methods, 3D printing requires more stringent ink. 3D printing can draw patterns by printing repeated lines or ink droplets on a substrate, which is more conducive to printing smaller electronic devices than other printing methods[36].
4 Conductive Mechanism of Conductive Polymer Composites Based on Nano-carbon Filler
Conductivity of conductive nanocomposites is one of the key parameters directly related to the performance of stretchable electronic devices. However, most polymers are not conductive, so conductive fillers are typically incorporated into the elastomeric polymer matrix to impart the desired conductivity. Conductive fillers form conductive pathways in the polymer matrix, and the conductivity represents the ability of electrons to transport through the conductive pathways. The conductivity of these elastic conductive composites can be analyzed and predicted using percolation theory, which aims to describe the connectivity between randomly distributed conductive fillers in an insulating elastomer medium[38]. The percolation theory is also the most studied conduction mechanism at present.
The most important concept in percolation theory is the percolation threshold, which is defined as the minimum volume fraction of conductive filler required to form a continuous conductive path in a given composite[39]. As can be predicted from the definition, when the volume fraction of the conductive filler is below the percolation threshold, the composite is in a nearly insulating state because there is no complete conductive path; As the volume fraction approaches the percolation threshold, the composite transitions sharply from insulator to conductor with a small change, as shown in Figure 7. It is important to note that the percolation threshold only indicates the presence of a conductive path and does not determine the maximum conductivity of the composite. Therefore, in practice, a large amount of conductive filler exceeding the percolation threshold is often used to improve the conductivity of the composite. After studying the 2D or 3D percolation network of elastic conductive composites composed of elastic polymers and conductive nanofillers, the formula (1) for predicting the conductivity of composites was summarized:[40]
Where σ is the conductivity of the composite, σ0 is the intrinsic conductivity of the conductive filler, φ is the volume fraction of the conductive filler, φ0 is the percolation threshold, and t is a constant (it is generally believed that when t is between 1.1 and 1.3, the conductive composite is a two-dimensional conductive network system; When the value of t is 1.6 ~ 2.0, the interior of the conductive composite is a three-dimensional conductive network system)[41].
In general, conductive fillers with a high aspect ratio and some ability to orient tend to have a low percolation threshold. Due to the continuous progress in the synthesis of nanomaterials, there are now many conductive fillers with high aspect ratio, such as carbon nanotubes, which can be used to prepare elastic conductors. However, the extreme arrangement of conductive fillers (high aspect ratio conductive fillers parallel to each other) also reduces the conductivity of the percolation network. The practical application of conductive fillers on elastic conductors requires a variety of analyses, which often need to be combined because the actual operating results are often different from the theoretical predictions. The essence of percolation theory is that when the distance between conductive filler particles is less than 1 nm, ohmic contact occurs to form a conductive path, and the higher the content of conductive filler, the greater the probability of mutual contact, the more perfect the conductive network, and the better the conductivity of the composite. When the content of conductive filler in elastic conductive composites is less than the percolation threshold, it is often considered that the distance between conductive particles is more than 10 nm, the electric field formed is small, and the tunneling effect theory of tunneling current generated by electron transition through thermal vibration is dominant[42,43]. When the content of the conductive filler in the composite is close to the percolation threshold, it is considered that the spacing of the conductive particles is between 1 and 10 nm, and the field emission theory is dominant, that is, an emission electric field is generated between the conductive particles, and electrons pass through the insulating layer to form a current. Therefore, the conductive mechanism of elastic conductors in practical applications is often not single[44].
5 Application
5.1 Stretchable sensor
Compared with other conductive fillers, carbon materials have unique advantages, such as good conductivity, excellent stability, good biocompatibility and easy functionalization[45,46]. However, there are many kinds of carbon materials, and the conductive networks formed are also different. If the resistance of the conductive composite changes regularly under strain and returns to the initial value after strain relief, it shows that the material has excellent sensitivity and cycle stability. Therefore, the stretchable conductive composite material prepared based on the nano-carbon filler can be widely applied to various stretchable sensor fields, such as strain sensors, pressure sensors, temperature sensors and the like, as shown in Table 1.
5.2 Stretchable energy storage device
The function of traditional batteries or supercapacitors often declines or even loses when they are subjected to external forces such as stretching and bending, so the stretchability of energy storage devices has become a hot research topic[52]. When the conductive network in the conductive polymer composite prepared based on nano-carbon filler can maintain stable connectivity under strain, and the composite can maintain structural integrity, it shows that the material has excellent tensile conductivity. Therefore, the stretchable conductive polymer composite prepared based on the nano-carbon filler can be used as an electrode, applied to a supercapacitor, applied to a battery as a current collector, or applied to an energy collection device such as a nano-generator, as shown in Table 2.
In addition to stretchable sensors and stretchable energy storage devices, stretchable conductive polymer composites based on nano-carbon fillers have many other applications. Someya et al. mixed single-walled carbon nanotubes with fluorinated rubber, resulting in a composite material with conductivity greater than 100 S·cm-1 and stretchability greater than 100%, and successfully constructed a stretchable active matrix display (Fig. 8A)[18]. Liu et al. prepared a conductive composite with excellent conductivity by mixing rGO and carbon nanotubes with styrene-butadiene rubber through emulsion mixing, and used it as a stretchable conductor (Fig. 8B)[20]. Kim et al. Used graphene foam and polydimethylsiloxane to prepare a stretchable graphene honeycomb structure with 72 S·m-1 conductivity, and successfully prepared a stretchable light-emitting display using this material as a circuit (Fig. 8C)[25].
6 Conclusion
Conductive stretchable nanocomposites are important components of new stretchable electronic devices.However, noble metal conductive fillers are expensive and have poor chemical stability, so noble metal conductive nanocomposites can not be produced and applied in large scale in stretchable electronic devices. The preparation of conductive nanocomposites with carbon fillers provides a new research direction for stretchable electronic devices. In this paper, the types of carbon conductive fillers, the preparation methods and conductive mechanism of composites, and the applications of conductive polymer composites based on nano-carbon fillers in different fields are reviewed.
However, the research and application of conductive polymer composites based on nano-carbon fillers are still in the initial stage, and still face many problems and challenges.Uch as poor dispersion of conductive fillers, unstable conductive network and inability to produce on a large scale, which limit the further development of composites in the field of stretchable electronics. In the future, the research on the conductive polymer composites based on carbon nanoparticles will focus on the following aspects: (1) selecting appropriate mixing methods and using certain chemical additives to improve the dispersion of conductive fillers in the polymer; (2) a plurality of carbon materials are used together to construct a stable and efficient conductive network; (3) that carbon material has strong modif capability and needs to be modify according to the specific application; And (4) realizing the miniaturization and scale of the preparation of the stretchable electronic device by using a novel printing technology. Through the summary of the existing research, it is expected that the conductive polymer composites based on nano-carbon fillers can be better applied in the field of stretchable electronic devices, and promote the progress of related research fields.
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