Highly Conductive Flexible Conductor Based on PEDOT:PSS/MWCNTs Nano Composite

Abstract

Flexible textiles with strong electrical conductivities have enormous potential as active components in wearable electronics. In this study, we fabricated highly flexible electrical conductors based on cotton fabrics using multiwalled carbon nanotubes (MWCNTs) and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) nanocomposites. We propose that mixing and drop-casting with different amounts of MWCNTs and a fixed amount of doped PEDOT:PSS using a cotton fabric provides a wide range of conductivities depending on the amount of MWCNTs in the mixture. Scanning electron microscopy (SEM) confirmed that the distribution of MWCNTs in the PEDOT:PSS films coated the surface of the cotton fabric, thereby increasing its electrical conductivity. We found that the amount of MWCNTs significantly affected the electrical properties of the nanocomposite cotton in two ways. First, the sheet resistance of the nanocomposite cotton decreased from 78.35 Ω/□ to 2.86 Ω/□ when the concentration of the nanocomposite was increased from 9.21 wt% to 60.27 wt%. This implies that the electrical properties of the nanocomposite cotton can be adjusted by controlling the amount of MWCNTs in the blend. Moreover, we found that the relationship between the sheet resistance and nanocomposite concentration obeys the power law with an exponent α ~ 1.676. Second, the study of the effect of temperature on the resistance indicates that the conductive nanocomposite exhibits semiconductor behavior in the temperature range 24–120 °C and obeys the variable range hopping model. The characteristic temperatures, resistance prefactor, and density of localized states and activation energies depend on the concentration of MWCNTs and can be described by power laws with exponents of 0.470, −1.292, −0.470 and 0.118, respectively. The novel nanocomposite cotton fabric developed in this study exhibits suitable electrical and thermal properties and good long-term electrical stability, which make the nanocomposite cotton fabric a potential flexible conductor with a wide range of electrical conductivities, making it suitable for various applications.

1. Introduction

The good electrical properties of electronic textiles make them suitable in the field of smart textiles. Recently, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been used to produce conductive textiles owing to its exceptional properties, such as water solubility, relatively high conductivity, excellent stability, excellent processability, and easy availability [1,2,3,4]. Alamer fabricated conductive cotton fabrics using PEDOT:PSS as the conductive material, dimethyl sulfoxide (DMSO) as the secondary dopant, and the drop-casting method, which exhibited a wide range of electrical conductivity. The conductivity of the fabric was found to depend on the concentration of PEDOT:PSS and to have a minimum sheet resistance of 1.58 Ω/sq [5]. The resistance of these fabrics as a function of temperature showed metallic semiconductor behavior [5,6]. It was also found that the electrical conductivity in the form of sheet resistance depends on the type of cotton fabric [7]. Although the electrical conductivity of PEDOT:PSS is improved by dopants such as polar solvents, for example, DMSO or strong acids, these dopants irritate the skin or damage the fabric [5,6,7,8,9,10]. Therefore, it is necessary to improve the conductivity of PEDOT:PSS without damaging the fabric or causing skin irritation. To overcome these problems, carbon nanotubes (CNTs), a conductive dopant, are widely used to dope PEDOT:PSS, resulting in a nanocomposite of CNTs/PEDOT:PSS, which has high electrical conductivity owing to its low density, high elastic modulus, high flexibility, and good electrical and thermal properties. This nanocomposite can be used to fabricate conductive textiles; however, so far, significant attention has been paid to the effect of CNT/PEDOT:PSS nanocomposite on substrates such as glass [11,12,13,14]. Their use in textiles has been largely ignored compared with the research conducted on substrates [15,16,17,18,19,20,21].

Flexible electrodes based on nylon paper as the substrate and a nanocomposite of PEDOT:PSS coated with MWCNTs/MnO₂ were fabricated in the study presented by Lee et al. [22] using Triton X-100 for the wettability of the MWCNTs, and the vacuum filtration method was used for the fabrication process. The results indicated that the sheet resistance of the nanocomposite nylon paper decreased with increasing nanocomposite concentration, reaching a minimum value of 23.6 Ω/sq at a concentration of 50 wt%. In addition, the conductive electrodes exhibited a high specific capacitance of 428.2 Fg⁻¹ and a high energy density of 63.8 Wh kg⁻¹. Sun et al. [23] prepared conductive silk fabrics from PEDOT: PSS/MWCNT nanocomposite and polypyrrole. The nanocomposite was dropped onto the fabric and polypyrrole was applied to the sample by in situ electropolymerization. The results showed that the treated conductive silk fabrics could be used as electrodes in supercapacitors owing to their low sheet resistance of 1.57 Ω/sq and capacitance of 5296 mF cm⁻² at a current density of 2 mA cm⁻², as well as their long cycle life. In another study, a flexible conductive heater was screen-printed using a Mylar substrate and a nanocomposite of PEDOT:PSS/MWCNTs ink (Pillai et al.) [24]. The results demonstrated that the stability of the nanocomposite ink was improved owing to the π–π interactions between PEDOT: PSS and MWCNTs. In addition, the conductive nanocomposite substrate exhibited a low sheet resistance of 51.31 Ω/sq, uniform temperature distribution, a peak temperature of 136 °C, and a power density of 0.137 W/cm².

In this study, nanocomposites of MWCNTs and doped PEDOT:PSS were used to prepare conductive cotton by the drop-casting method using different amounts of MWCNTs and a fixed amount of PEDOT:PSS to prepare aqueous solutions of the nanocomposites. The proposed method is simple and consists of two steps: drop-casting for the preparation of flexible conductors. The novelty lies in the preparation of flexible nanocomposite conductors with smaller amounts of PEDOT:PSS and variable amounts of MWCNTs. The fabricated nanocomposites were conductive, flexible, lightweight, low-cost, and could be used in portable electronic devices. To the best of our knowledge, we have the lowest sheet resistance of 2.86 Ω/□ at a nanocomposite concentration of 60.27 wt% obtained, compared with other reports on nanocomposites. Electrical studies showed that the conductive nanocomposite fabrics were affected by the amount of MWCNTs in the mixture over a wide temperature range of 24–120 °C and suppressed semiconductor behavior. The morphology, elemental composition, thermal behavior, and structural and phase identifying properties of the conductive nanocomposite cotton fabric were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD).

2. Experimental

2.1. Materials

Cotton fabric was purchased from FPC, SA. MWCNTs and PEDOT:PSS (1.3 wt% dispersion in H₂O) were purchased from Sigma Aldrich, UK, and used as conducting materials. The DMSO (assay 99.9%) was purchased from Sigma Aldrich, UK, and used as a secondary dopant to improve the electrical properties of the PEDOT:PSS.

2.2. Preparation of the Conductive Nanocomposites

An extensive investigation was conducted to optimize the electrical properties of cotton fabrics treated with a PEDOT: PSS/MWCNT nanocomposite and to determine the optimum formulation of the nanocomposite to achieve high electrical conductivity and low sheet resistance. First, a doped PEDOT:PSS solution was prepared by mixing PEDOT:PSS with DMSO (volume fraction of 5 wt%). Subsequently, 20 solutions were prepared with a fixed amount of doped PEDOT:PSS and different amounts of MWCNTs. Each solution was sonicated for 30 min.

2.3. Preparation of Conductive Cotton Fabrics Based on Nanocomposite

The process for producing conductive cotton fabrics based on the PEDO: PSS/MWCNT nanocomposite was as follows. In total, 20 nanocomposite samples were applied to 20 cotton samples, each with an area of one square inch, by pouring the solution onto the top of the cotton fabrics. The treated cotton samples were stored at room temperature for half an hour. The cotton was then dried in an oven at 100 °C for one hour.

2.4. Characterization

The electrical resistances of the conductive nanocomposite cotton fabrics were measured using the four-line probe method, and the sheet resistances were calculated using the formula $R_s=Rw/d$, where $w$ is the width of the sample (2.5 cm) and $d$ is the distance between the lines (0.35 cm). The current was applied using a Keithley 2400 Standard Series SMU, while an HP 34410A millimeter was used to measure the potential difference. Scanning electron microscopy (SEM) was performed using a JSM-7610F instrument. Transmission electron microscopy (TEM) was performed using a JEM-1400 instrument at an accelerating voltage of 200 kV. The TEM Samples were prepared by applying a drop of a colloid solution to a 400 mesh copper grid coated with an amorphous carbon film and subsequently evaporating the solvent in air at room temperature. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed using a TGA-1000 and DSC-8000 instrument, respectively. The samples were heated under a nitrogen purge from 25 °C to 600 °C at a heating rate of 10 °C/min. The XRD patterns were recorded using a Rigaku D/max-2500 diffractometer in conventional theta/2theta geometry.

3. Results and Discussion

3.1. Morphology Study

In the SEM image of the untreated cotton fabric (Figure 1A), the fibers, the space between them, the fiber groups, and a smooth and uniform surface can be clearly observed. The SEM image of the conductive nanocomposite cotton fabric (Figure 1B) shows a rough surface because PEDOT:PSS coats the fibers, and the MWCNTs are randomly distributed in the polymer matrix (bright dots). It was observed that the addition of the nanocomposite changed the surface of the cotton fabric from a smooth surface to a rough surface. This is attributed to the effect of the DMSO in the nanocomposite mixture, which is associated with the manufacturing process in which the MWCNTs in the nanocomposite mixture are suspended in the DMSO in an ultrasonic bath. In addition, the physical appearance of the cotton fabric could be affected by the DMSO and changed from a twisted ribbon-like structure to a film, as shown in Figure 2B, because DMSO is the aprotic solvent that partially dissociates to [CH3COO-], which interacts with the cellulose molecules and improves their dissolution [25,26,27]. The SEM explains the reason for generating the electrical conductivity in the nanocomposite cotton fabric by forming electrical conduction paths. The grain size was calculated using Image J online software using the relative Average grain size = line length/number of grains, which was 3.79 µm.

The TEM image of the nanocomposite cotton fabric (Figure 1C) shows a non-smooth surface and the PEDOT:PSS coating, as well as the outer wall of the MWCNTs; a gradient of PEDOT/PSS crystallinity exists around the MWCNTs, as shown in the study presented by Zhou and Lubineau [28]. This is due to the strong π–π stacking interaction between the thiophene rings in PEDOT and the surface of the MWCNTs, which results in the amorphous PSS being located in the outer part of the PEDOT/PSS-coated MWCNTs. To determine the elemental composition, energy-dispersive X-ray spectroscopy (EDX) measurements were performed on pure cotton and cotton fabric treated with the nanocomposite.

3.2. Elemental Analysis

Table 1. EDX analysis of pure cotton and conductive cotton treated with the nanocomposite.

	Pure Cotton		15.61 wt%		17.83 wt%
Element	E (keV)	At (%)	E (keV)	At (%)	E (keV)	At (%)
Carbon	0.277	48.10	0.277	54.30	0.277	55.00
Oxygen	0.525	51.9	0.525	37.70	0.525	35.00
Sulfur	-	-	2.307	8.00	2.307	10.00

shows the EDX analysis of pure cotton and cotton treated with the nanocomposite at two concentrations. The EDX analysis of pure cotton showed peaks at 0.277 keV and 0.525 keV, indicating the presence of carbon and oxygen, respectively, owing to the cellulose structure. The atomic percentages of carbon and oxygen are 48.10 and 51.90%, respectively. The EDX measurements of the treated cotton at 15.61 wt% and 17.83 wt% showed an additional peak at 2.307 keV, indicating the presence of sulfur, in addition to the presence of carbon and oxygen associated with the atomic sulfur in the thiophene ring and the sulfonic groups of PEDOT:PSS. Moreover, the atomic carbon content increases with increasing MWCNT concentration.

3.3. Thermal Analysis

Thermal degradation: The effect of the amount of PEDOT: PSS/MWCNT nanocomposite on the thermal degradation of conductive nanocomposite cotton was investigated to understand the change in thermal degradation. Figure 2A shows the thermogravimetric analysis (TGA) of the untreated cotton and the treated cotton with nanocomposites of 24.69, 35.87 and 77.24 wt%, respectively. The TGA of the untreated cotton fabric showed a small weight loss at 135 °C due to moisture content removal, and for the cotton fabrics treated with the nanocomposite, the small transition at 155 °C is due to moisture content removal. The degradation of untreated cotton fabric starts at approximately 310 °C (the onset temperature) and reaches its maximum weight loss at approximately 400 °C (the decomposition temperature), which is due to depolymerization by transglycosylation reactions (red curve in Figure 2A). Conversely, the onset temperature and decomposition temperature of the treated cotton fabric with different concentrations of the PEDOT: PSS/MWCNT nanocomposite starts at approximately 210 °C and 373 °C, respectively, which is lower than the onset and decomposition temperatures of the untreated cotton fabric. This is attributed to the lower thermal stability of PEDOT/PSS, which affects the overall thermal degradation. In addition, it is clear that the thermal degradation of the nanocomposite samples was independent of the concentration, as shown in Figure 2A.

DSC analysis: Figure 2B shows the DSC analysis of the cotton fabric treated with the nanocomposite. The samples were heated under a nitrogen purge from 25 °C to 600 °C at a heating rate of 10 °C/min. It can be seen that the initial endothermic peak of the treated and untreated cotton is around 80 °C, which is due to the dehydration of moisture. Moreover, a sharp endothermic peak for decomposition was observed at 347 °C for the untreated cotton, while a double broad endothermic peak was observed at approximately 271 °C and 347 °C for the nanocomposite treated cotton, indicating the influence of the nanocomposite.

3.4. XRD Analysis

The XRD patterns of the untreated cotton fabrics and those treated with different concentrations of the nanocomposite are shown in Figure 3A. It is clear that the diffraction peaks of the untreated and treated cotton samples are the same, indicating that the crystalline region of cellulose is largely unaffected by the presence of the nanocomposite, which could be explained by the merging of the peaks of the nanocomposite with the broader peak of the untreated cotton at (200). The diffraction peaks are shown as follows: (1-1 0) at 2θ = 14.7°; (110) at 2θ = 16.6°; (021) at 2θ = 20.6°; (002) at 2θ = 22.7°; and (040) at 2θ = 34.7°, corresponding to the crystalline structure of cellulose Iβ and cellulose [29].

3.5. Investigation of the Electrical Properties

3.5.1. Sheet Resistance Measurement

The main objective of this work was to transform the electrically insulating behavior of cotton fabric into highly conductive behavior using PEDOT: PSS/MWCNT nanocomposites, which can be investigated by studying the effect of nanocomposite concentration on the sheet resistance of cotton fabric. For the nanocomposite concentration, the amount of PEDOT:PSS was fixed at 2.7 wt% and the MWCNTs concentration was changed from 9.21 wt% to 57.57 wt%. As shown in

Table 2. Sheet resistance measurements as a function of nanocomposite concentration for a fixed amount of PEDOT:PSS (2.70 wt%) and varying amounts of MWCNTs.

C (wt)	9.21	15.61	17.83	21.04	28.42	30.62	34.60	36.75	41.62	48.06	50.46	54.1	60.27
Rs (Ω/□)	78.36	26.57	18.21	17.36	11.43	9.79	7.50	6.36	5.29	4.64	4.36	3.43	2.86

, the introduction of a small, fixed amount of doped PEDOT:PSS (2.7 wt%) reduced the sheet resistance by up to five orders of magnitude, from 1 GΩ/□ to 53.94 kΩ/□ for the untreated and treated cotton fabrics, respectively. When cotton was treated with the nanocomposite containing the same amount of PEDOT:PSS, but with 6.61 wt% MWCNTs, the sheet resistance decreased by up to three orders of magnitude, reaching a value of 78.35 Ω/□. With an increasing concentration of MWCNTs in the nanocomposite, but at a fixed amount of PEDOT:PSS, the sheet resistance decreases and reaches the minimum value of 2.86 Ω/□ at a nanocomposite concentration of 60.27 wt%, indicating high electrical conductivity. This could be explained as follows: when PEDOT:PSS is doped with MWCNTs, a π–π interaction exists between them because MWCNTs have free electrons moving freely between the p orbitals and forming a π-bonding network, and PEDOT:PSS has free electrons moving in a long π-conjugated system.

3.5.2. Theoretical Analysis

To determine the nature of the relationship between the sheet resistance of the conductive cotton fabric and the concentration of the nanocomposite, the logarithm of $R_s$ was plotted against the logarithm of C, and the equation of the fitting line and the corresponding R² value were determined. As can be seen in Figure 3B, the fit line produced a good straight line with an R² value of 98.78%, satisfying the equation:

$$\log R_s\left(C\right)=a-\alpha \log C$$

(1)

where $a$ and $\alpha$ are the fitting parameters with values of 3.449 and 1.676, respectively. Therefore, Equation (1) explains that $R_s$ is proportional to the power of C and can be written in terms of the power law as follows:

$$R_s\left(C\right)=\frac{a}{C^{\alpha }}$$

(2)

3.5.3. Temperature Study

The resistance-temperature dependence of the conductive nanocomposite cotton was investigated in the temperature range of 24–120 °C, and the nanocomposite had different amounts of MWCNTs at 6.51 wt%, 37.32 wt%, and 47.76 wt%, and with a fixed amount of PEDOT:PSS at 2.7 wt%. As shown in Figure 4, the resistance decreased linearly with increasing temperature, indicating a semiconductor behavior. The changes in resistance are from 114.1 to 71.2 Ω (42.9 Ω) for the 6.51 wt% concentration, from 91.1 to 44.6 Ω (46.5 Ω) for the 37.32 wt% concentration, and from 77 to 36.6 Ω (40.4 Ω) for the 50.46 wt% concentration.

3.5.4. Temperature Analysis

For the temperature-dependent resistance R(T) of the conductive nanocomposite fabric at low bias voltage, the variable-range-hopping (VRH) model [30,31,32] predicts that

$$R\left(T\right)=R_0{e}^{{\left(\frac{T_0}{T}\right)}^{\frac{1}{2}}},$$

(3)

where $R_0$ is the resistance prefactor and $T_0$ is the characteristic temperature coefficient, which is measured by the degree of disorder. The plots between $\ln R$ and $T^{-\frac{1}{2}}$ for the nanocomposite samples are shown in Figure 4B. The fitted values of $T_0$, $R_0$ and the values of $R$ at low and high temperatures for both concentrations are shown in

Table 3. VRH fitting parameters for the nanocomposite samples at fixed amount of PEDOT:PSS and different concentrations of MWCNTs.

Sample	C (wt%)	${\mathit{T}}_0\left(\mathit{K}\right)$	${\mathit{R}}_0($Ω)	$\mathit{N}\left({\mathit{E}}_{\mathit{f}}\right)$ (eV)	$\mathit{R}$ (303 K)	$\mathit{R}$ (388 K)
1	6.51	$4.54\times {10}^3$	2.39	6.642	112.50	71.20
2	37.72	$1.07\times {10}^4$	0.24	2.827	90.60	44.60
3	47.76	$1.14\times {10}^4$	0.18	2.654	75.40	36.60

. The plots between $T_0$ and C and between $R_0$ and C for the nanocomposite samples are shown in Figure 5. In Figure 5A,B, the connections between the measurement points have been inserted to determine the exact relationship between $T_0$ and C and between $R_0$ and C, respectively. As can be seen in Figure 5A, the characteristic temperature increases with the increasing concentration of MWCNTs in the nanocomposite, which can be described by the empirical relation, the fitting relation, and $T_0\propto C_{MWCNTs}^{0.47}$, with $R^2=$ 0.998. The values of the resistance prefactor presented in Figure 5B indicate that the resistance prefactor decreases with the increasing concentration of MWCNTs and can be described by the power law according to the fitting relation $R_0\propto C_{MWCNTs}^{-1.292}$ with $R^2=1$.

3.5.5. Density of Localized State $N\left(E_{\mathrm{F}}\right)$

The density of the localized states at the Fermi level was also analyzed to obtain more information about the characteristics of the electrical properties of the conductive nanocomposite cotton fabrics at different concentrations of MWCNTs. First, $N\left(E_F\right)$ is calculated from the relation

$$N\left(E_F\right)=\frac{24}{\pi k_B{T}_{0{\zeta }^2}}$$

(4)

where $k_B$ is the Boltzmann constant ($8.617\times {10}^{-5}eV{K}^{-1}$) and $\zeta$ is the decay length of the localized polaron wavefunction, which is equal to the distance between cation and cation for the octahedral sites (2.94). The plots between $N\left(E_F\right)$ and C, Figure 5C, showed that the density localized state decreases with the increasing concentration of MWCNTs, and can be described by the power law according to the fitting relation $N\left(E_F\right)\propto C_{MWCNTs}^{-0.47}$ with $R^2=$ 0.998.

3.5.6. Activation Energy

The temperature-dependent activation energy of the conductive nanocomposite fabric was also calculated using the equation

$$w=0.25k_B{T}_0^{\frac{1}{4}}{T}^{\frac{3}{4}}$$

(5)

The plots between w and T, Figure 6A, show that the activation energy increases with increasing temperature. The activation energy increases from $1.27\times {10}^{-2}$ to $1.55\times {10}^{-2}eV$ and from $1.57\times {10}^{-2}$ to $1.91\times {10}^{-2}eV$ and from $1.59\times {10}^{-2}$ to $1.94\times {10}^{-2}eV$ for the cotton fabrics treated with nanocomposite that contains MWCNTs of 6.51 wt%, 37.32 wt%, and 47.76 wt%, respectively. To find out the effect of MWCNT concentration on activation energy, the relationship between w and C was investigated at three different temperatures, namely 303, 338 and 378 K, as shown in Figure 6B. The relation between w and C can be described by the power law according to the fitting equation $w\propto C_{MWCNTs}^{0.1175}$ with $R^2=$0.998.

3.5.7. Sheet Resistance Stability

This method investigated the electrical stability of the long-term behavior of the conductive nanocomposite cotton at room temperature, with low, medium, and high concentrations of 9.21, 21.94, and 50.46 wt%, over a period of eight weeks, as shown in Figure 7. Our observations showed that cotton treated with a low concentration was stable for up to five weeks. Subsequently, the sample became unstable as the sheet resistance increased by 24.97%, reaching a value of 97.92 Ω/□ after eight weeks. The medium concentration sample showed electrical stability up to five weeks, after which the sample became unstable as the sheet resistance increased by 18.53% and reached a value of 20.57 Ω/□. Finally, the highly concentrated sample was more stable up to six weeks; a slight change in the sheet resistance value of 4.92% was observed, and the sheet resistance reached a value of 4.57 Ω/□. The stability study showed that the electrical stability of the conductive nanocomposite cottons over a period of eight weeks depended on the amount of MWCNTs in the nanocomposite, and the sample with the highest concentration was more stable than the other samples.

4. Conclusions

A novel flexible nanocomposite conductor with a wide conductivity range, based on cotton fabrics and a nanocomposite of PEDOT:PSS and MWCNTs, was developed. The morphological, structural, thermal, and electrical properties of the nanocomposite cotton fabrics were characterized. The results indicate that the MWCNTs are randomly distributed in the polymer matrix, and PEDOT:PSS coats the outer wall of the MWCNTs, as well as the fibers and the interstitial space between them. The XRD patterns of the nanocomposite cotton fabrics were similar to those of the untreated cotton fabric and were independent of the nanocomposite concentration. A thermal study demonstrated that the decomposition temperature of the nanocomposite fabrics was lower than that of pure cotton. A double broad endothermic peak was observed at approximately 271 and 347 °C, which was independent of the nanocomposite concentration. Incorporating MWCNTs into a small, fixed amount of PEDOT:PSS is an effective method to fabricate flexible conductors. By controlling the amount of MWCNTs in the nanocomposite, conductors with a wide range of electrical conductivities can be fabricated. A highly conductive nanocomposite cotton fabric with a sheet resistance of 2.86 Ω/□ was fabricated using a nanocomposite concentration of 60.27 wt%. The temperature dependence of ohmic resistance for the nanocomposite treated cotton fabrics was consistent with the variable range hopping model. It was found that the characteristic temperatures, resistance prefactor, density of localized states, and activation energies, depend on the concentration of MWCNTs in the nanocomposite and obey the power law relationship. It is worth mentioning that the cotton fabrics with low and medium nanocomposite concentrations were stable for up to five weeks, which, subsequently, became unstable owing to the change in sheet resistance. However, the high-concentration cotton fabric was stable for up to six weeks and showed a slight change in the sheet resistance. Using this safe, simple, cost-effective, and environmentally friendly method, conductive nanocomposite cotton fabrics can be used to fabricate electrodes, capacitors, conductive wires, and functional fabrics in wearable electronics.