Surface functionalization of Ag/polypyrrole-coated cotton fabric by in situ polymerization and magnetron sputtering

Abstract

Flexible electronic devices have attracted considerable attention in recent years, and textile fabrics are usually used as the substrates because of their good moisture absorption performance and high flexibility. However, ordinary textile fabrics are electrically insulating, which limits their strain sensing sensitivity. In this study, cotton fabric endowed with high electrical conductivity was prepared by a two-step process of in situ polymerization and direct current (DC) magnetron sputtering. It was firstly modified with a continuous polypyrrole (PPy) thin film by using the in situ polymerization method and then coated with silver (Ag) thin film by using a DC magnetron sputtering system. The experimental results revealed that the resultant Ag/PPy-coated cotton deposited with a sputtering power of 200 W for 25 min has the highest electrical conductivity and its average sheet resistance is 11.7 Ω/sq. Moreover, the Ag/PPy-coated cotton exhibited the advantages of high hydrophobicity, thermal stability, electromechanical performance and washing fastness. Overall, the effective flexibility and high electrical conductivity of the Ag/PPy-coated cotton have been validated effectively and make it one of the promising candidates for preparing electromagnetic shielding and antistatic and smart wearable textile products, especially flexible electronic devices.

Keywords

polypyrrole Ag thin film in situ polymerization magnetron sputtering

In recent decades, flexible and wearable electronic devices have attracted considerable attention because of their great potential applications in smart clothing, biomedical devices, energy conversion and storage, electromagnetic interference shielding, etc.^1–3 Compared to traditional electronics, flexible electronic devices possess many superior advantages, including good flexibility, light weight, high sensitivity and deformation ability.^4–10 However, most of them are made of conductive metal nanoparticles or nanowires, metal thin films and carbon nanotubes, leading to an unsatisfactory air permeability of the devices.^11–13 In this case, textiles possessing many unique features, such as a porous structure, good moisture absorption performance, light weight, good flexibility and recoverable deformation, can be used as one of the promising substrate candidates in the preparation of electronic devices.^14,15

In addition, magnetron sputtering provides a promising approach for the deposition of thin films due to its outstanding advantages, such as simplicity, high speed, low working temperature and being suitable for sputtering many kinds of materials.^16–18 Therefore, many researchers have dedicated their efforts to endow the textiles with different performances by sputtering functional thin film onto the fabric surface. Miao et al.¹⁹ deposited silver (Ag) and AZO (ZnO:Al₂O₃ = 98wt%:2wt%)/Ag/AZO ceramic onto the cotton fabrics by radio frequency (RF) magnetron sputtering, and found that the AZO/Ag/AZO-coated cotton fabrics exhibited an infrared reflection rate of 18% and the highest ultraviolet protection factor (UPF) values of 21.782. The result shows that the prepared flexible cotton fabrics can provide UV radiation protection and infrared reflective properties, which make this material promising for solar control applications. Sanjines et al.²⁰ prepared antimicrobial fabrics by bipolar asymmetric direct current (DC) pulse magnetron sputtering (DCP), and the result indicated that the fastest Escherichia coli inactivation was observed within 10 min when copper (Cu) was sputtered on cotton for 60 s. Jiang et al.²¹ produced functional polyester fabric with nanostructured Ag film by magnetron sputtering. The result revealed that the Ag-coated polyester fabrics possess excellent UV protection and hydrophobicity (contact angle = 132.2°) and good antibacterial performance. Yuan et al.²² fabricated silver/titanium dioxide (Ag/TiO₂) polyester fabric by using DC magnetron sputtering and RF magnetron reaction sputtering techniques with pure Ag and titanium (Ti) targets. Compared with the original fabric samples, it is observed that the anti-UV properties and antistatic properties of the fabrics deposited with Ag/TiO₂ composite films were improved significantly, while, different structural colors of the coated fabrics were generated.

Many researchers have focused on the preparation of conductive materials by magnetron sputtering. However, there are few studies about the preparation of conductive materials using flexible textiles as the substrate by using magnetron sputtering. Moreover, the surface roughness of fabric and the gap between the fibers/yarns would cause a discontinuous conductive network and a high electrical resistance after magnetron sputtering. These would limit the application of metal magnetron sputtering in fabricating highly conductive textiles. To solve the problem, here we propose a method in which a primary conducting network can be firstly formed on the surface of cotton fabric, and then Ag nanoparticles are deposited by magnetron sputtering to realize the fabrication of electro-conductive cotton fabric.

In more recent years, polypyrrole (PPy) as a π-conjugated polymer has been widely studied and it offers many advantages, such as high thermal and chemical strength, good conductivity and mechanical flexibility.^23–26 The combination of PPy and deposited metal thin film can create a complete conductive network, enhancing the electrical conductivity of the resultant fabric.

In this study, highly electrical conductive cotton fabric was prepared by using a combined method of in situ polymerization and DC magnetron sputtering. Firstly, conductive cotton fabric was obtained by dipping the cotton with pyrrole (Py) following by an in situ polymerization with ferric chloride. Then the PPy-coated cotton fabric was sputtering with the Ag target to acquire higher conductivity. The influences of polymerization and sputtering parameters on the surface morphology, thermal stability, wettability, mechanical properties, electrical conductivity, electromechanical performance and washing fastness of the prepared conductive fabrics are systematically investigated. The resultant Ag/PPy-coated cotton fabric with high conductivity has potential applications in the fields of electromagnetic shielding and antistatic and smart wearable textiles.^1,7,10,15

Experimental details

Materials

Py (mass fraction: 98%) and ferric chloride (FeCl₃·6H₂O; molecular weight = 270.3) were supplied by Sinopharm Chemical Reagent Co., Ltd (China). White weave cotton fabric [fabric weave: plain; density (warp/cm×weft/cm): 130 × 130; gram weight: 60 g/m²] used as a substrate material was provided by Yinjing Medical Technology Co., Ltd (China). The silver (Ag) target with diameter of Φ80 × 6 mm (purity: 99.99%) was supplied by LuoYang Lingshi New Material Technology Co., Ltd. All reagents used in this study were of analytical grade.

Preparation of PPy-coated cotton fabric

PPy-coated cotton fabric was prepared by an in situ polymerization. Firstly, a cleaning process was carried out on the cotton fabric to remove the contaminants and improve the adhesion between the fabric and the polymer. The cotton fabric (20 cm × 20 cm) was soaked in an acetone solution for 2 h and then washed thoroughly with deionized water, followed by drying in an oven at 80℃ for 2 h. After that, the fabric was dipped into the Py dispersed solution with different molar concentrations (0.2, 0.4, 0.6, 0.8 and 1.0 mol/L) at 0℃ for 30 min. Then the initiator (FeCl₃·6H₂O) with a molar ratio of Py monomer to oxidant of 3:1 was added in the above solution and the optimal molar concentration of Py was chosen to investigate the influence of the polymerization time (30, 60, 90, 120, 150 and 180 min) on the conductivity of the PPy-coated cotton fabric. The resultant PPy-coated cotton fabric can be obtained after rinsing five times with deionized water and subsequently drying in an oven at 80℃ for 24 h.

Preparation of Ag/PPy-coated cotton fabric

Ag/PPy-coated cotton fabric was prepared by a DC magnetron sputtering system (model: MSP-300C). Prior to deposition, the vacuum chamber was evacuated down to a base pressure of 5.0 × 10⁻⁴ Pa. The distance between the substrate and target was fixed at 150 mm. To improve the uniformity of the deposited film, a substrate holder was introduced and rotated at a speed of 100 r/min. During the deposition, the argon flow rate was kept at 10 mL/min and the gas pressure of the vacuum chamber was 0.8 Pa. The sputtering process was carried out at room temperature. The investigated deposition parameters are shown in Table 1. Figure 1 shows the entire preparation process of Ag/PPy-coated cotton fabric.

Figure 1.

Preparation process of Ag/PPy-coated cotton fabric. Py: pyrrole; PPy: polypyrrole.

Table 1.

Deposition parameters

Parameter	Investigated range of parameter
Sputtering power/(W)	100, 150, 200, 250, 300 (The sputtering time was fixed at 10 min.)
Sputtering time/(min)	10, 15, 20, 25, 30 (The sputtering power was fixed at 200W.)

Characterization and measurement

The surface morphology of pure cotton as well as PPy-coated, Ag-coated and Ag/PPy-coated cotton was investigated by using a scanning electron microscope (SEM; JEOL JSM-840, Japan). The thermal stability of the samples was measured by thermogravimetric analysis (TGA, TGA 4000, USA). All of the TGAs were conducted with the following conditions: nitrogen gas at a flow rate of 20 mL/min; measurement temperature ranging from 30℃ to 800℃ with a heating rate of 15℃/min. The contact angle of water droplets on the surface of the samples was measured by using an optical contact angle measuring instrument (KRUSS DSA30, Germany). The mechanical properties (strength–strain curves) of the samples (length × width: 70 mm × 30 mm) were analyzed by using an XS (08) F2-250 Materials Testing System. The measurements of each sample were conducted five times, and the one closest to the average value was used for evaluation. Electrical conductivity of the samples was investigated by using a four-point probe system with a linear probe head (SZT-2C). The measurements of each sample were conducted five times on both the vertical and horizontal directions of the samples, and the average was used for evaluation. The electromechanical performance of the samples (changes in electric resistance of fabric samples at different strain levels) was recorded by using a combination of a material testing system and a multimeter. The washing fastness of the samples was tested by laundering the samples in a Launder machine for different washing cycles (5, 10, 15 and 20) at 40℃ with 5 g/L nonionic surfactant according to the GBT-3921-2008 standard: Textiles-tests for color fastness: color fastness to washing with soap or soap and soda.

Results and discussion

Surface morphology

Figure 2 shows the SEM images of the pure cotton and different coated cottons. As shown in Figure 2(a), the cotton exhibits a flat ribbon structure with irregular folds, and the fiber surface is rough. Figure 2(b) shows that the PPy particles with irregular spherical shape are successfully assembled on the cotton fiber and an agglomeration of PPy particles is also observed. As shown in Figures 2(c-II) and (c-III), silver particles with diameter of 300–400 nm are clearly visible on the cotton fiber after deposition. Clusters of silver particles are observed [Figure 2(c-I)] because they tend to merge with each other rather than with the electrical insulate substrate.²⁷ A similar result was reported by Jiang et al.²⁸ in which silver clusters were also observed on polyester fiber after sputtering. Figure 2(d) shows that silver particles with a small particle size of 200 nm was deposited onto the PPy-coated cotton. Compared with Ag-coated cotton, the Ag thin film on PPy-coated cotton is dense and the particle size distribution is uniform, but small cracks are also visible on the cotton fibers after deposition [Figure 2(d-III)].

Figure 2.

Scanning electron microscope images taken at different magnifications of (I) 500×, (II) 5000×, (III) 20000×: (a) cotton; (b) polypyrrole (PPy)-coated cotton; (c) Ag-coated cotton; (d) Ag/PPy-coated cotton. (The sputtering was conducted at 200 W for 10 min.)

Thermal stability

Figure 3 shows the thermogravimetry (TG) and derivative thermogravimetry (DTG) curves of different samples, and the important parameters corresponding to the thermal behaviors are summarized in Table 2. The thermal stability of PPy is also shown in Figure 3 for comparison. As shown in Figure 3(a), the residual mass of PPy at 800℃ is high at 60%, which indicates that the PPy has a good thermal stability at high temperature. Except for the PPy, the thermal decomposition of the samples can be analyzed as a decomposition process of weight loss and it can be divided into three stages.

Figure 3.

Thermogravimetry and derivative thermogravimetry curves of different samples. PPy: polypyrrole. (The sputtering was conducted at 200 W for 10 min.)

Table 2.

Parameters of different samples during the thermal decomposition

Sample	T₀ (℃)	T_d (℃)	a (%)
Cotton	277.72	357.30	2.36
PPy	223.31	280.53	59.79
Ag-coated cotton	277.72	378.61	11.66
PPy-coated cotton	223.79	374.08	13.32
Ag/PPy-coated cotton	223.79	344.51	30.62

T₀: thermal decomposition temperature at the beginning weight loss rate of the material; T_d thermal decomposition temperature at the maximum weight loss rate of the material; a: weight residue at 800℃; PPy: polypyrrole

The first stage is from room temperature to 277℃, and the weight loss at this stage might be due to the volatilization of moisture, the bound water among the material molecules and the decomposition of unstable oxygen-containing functional groups in the samples.²⁹

The second stage is from 277℃ to 400℃, and the weight loss at this stage can be attributed to the removal of oxygen functional groups in the samples, such as -COC-, -OH, -COOH. As can be observed in the TG curve, each sample shows a rapid thermal decomposition. Corresponding to the rapid decomposition, there is a mass loss peak in the DTG curve and the T_d (presented in Table 2) can be determined according to the value of the maximum peak. It is obvious that the starting point of the rapid decomposition of Ag-coated cotton is at about 378.61℃, which is higher than that of the other samples. This could be due to the good thermal insulation properties of Ag particles.^30,31 Moreover, the onset of the weight loss rapid thermal decomposition temperature of Ag/PPy-coated cotton is shifted to a lower temperature than that of cotton,³² which could be attributed to the decomposition of a small amount of prepolymer produced during in situ polymerization of PPy.

The third stage is a high-temperature phase of carbon formation ranging from 400℃ to 800℃. At this stage, most of the samples are carbonized and the rising temperature has less impact on the mass loss of residues. As depicted in Figure 3, the residual mass at 800℃ of PPy-coated cotton, Ag-coated cotton and Ag/PPy-coated cotton is higher than that of the cotton, which reveals that both the PPy particles and Ag deposited film can improve the thermal stability of cotton. In addition, Ag/PPy-coated cotton shows the highest weight residue at 800℃, indicating an improvement of the thermal stability of the cotton fabric. This is due to the excellent thermal stability of PPy polymerized inside the fiber matrix; Ag particles with a high melting point (960℃)³³ were deposited onto the PPy, which restricts the thermal motion of the PPy chains and shields the degradation of the polymer.³⁴ Therefore, it can provide a thermal insulation and protect the cotton from degradation.

Wettability

The wettability of fabric is mostly affected by its surface roughness, surface free energy and chemical composition.³⁵ The contact angle of cotton, PPy-coated cotton and Ag/PPy-coated cotton is shown in Figure 4. As can be seen in the figure, the water droplet disappears directly after dropping onto the cotton, which is attributed to its excellent hydrophilic property. The water contact angle of the PPy-coated cotton increased to 131℃ because the polymerization of Py on the cotton surface and inside the spaces between the cotton yarns can generate a low surface tension of the resultant fabric. Obviously, the Ag/PPy-coated cotton shows that a higher hydrophobicity and the water contact angle remains at 143℃ even after an observation for 2 min. This can be attributed to the Ag/PPy coating with a low surface energy exhibiting a low surface tension, which can transform the cotton from hydrophilic to hydrophobic.³⁶ Therefore, Ag/PPy-coated cotton endowed with the hydrophobic property has a wider application not only for indoor but also for outdoor environments.

Figure 4.

Water contact angle of different samples after 2 min. PPy: polypyrrole.

Mechanical properties

Typical strength–strain curves during the stretching of cotton (C), PPy-coated cotton (P) and Ag/PPy-coated cotton (A) are depicted in Figure 5. The curves are due to a two-step deformation mechanism typically attributed to the woven structure of fabric³⁷: at first, deformation involves only partial untangling of the fiber network and the reduction of fabric stiffness due to the shear deformation of the crimp (i.e., at the intersection of perpendicular fibers), and then the fibers are elongated until rupture. As shown in Figure 5, the breaking strength slightly increases after the fabric was coated with PPy, then decreases after the PPy-coated cotton was deposited with Ag particles. The increasing strength of the PPy-coated cotton may be due to the uniformly distributed polymer and the improved strong interactions between the cotton and PPy that was polymerized onto the fiber matrix. However, for the Ag/PPy-coated cotton, the cracks of Ag thin film observed would lead to a lower tensile strength.³⁸ As shown in Figure 5, the vertical coordinate (Y-axis) and the horizontal coordinate (X-axis) represent the stress and the strain (namely the breaking elongation) of samples, respectively. In this case, the stress retention rate can be expressed by the ratio of the Y-axis of coated fabric to the cotton, while the strain retention rate refers to the ratio of the X-axis of coated fabric to the cotton. According to Figure 5, the stress retention rate of Ag/PPy-coated cotton (A_Y-axis/C_Y-axis)³⁹ was 92%, and the strain retention rate (A_X-axis/C_X-axis) at the maximum stress was 239%. This result suggests that the Ag/PPy-coated cotton fabric is stable to the deformation retention under the maximum stress when compared with the cotton fabric.

Figure 5.

Stress–strain curves of different samples. PPy: polypyrrole. (The sputtering was conducted at 200 W for 10 min.)

Electrical conductivity

Textile materials have very high surface resistivity, and the value of cotton fabric is reported to be 10¹⁵ Ω/sq,⁴⁰ which shows that cotton fabrics are electrically non-conductive. In addition, the sheet resistance of Ag-coated cotton is also measured: the value is high at 10⁶ Ω/sq. The poor electrical conductivity can probably be attributed to the discontinuous and loose Ag thin film on cotton. Figure 6(a) shows the sheet resistance of PPy-coated cotton fabric as a function of the molar concentration of Py and polymerization time. As shown in Figure 6(a), the sheet resistance of the sample is still high at 60.9 kΩ/sq because the PPy polymerized with a low molar concentration of Py cannot constitute a continuous conductive circuit, leading to a poor conductivity. The sheet resistance of the fabrics decreases obviously as the Py molar concentration increased from 0.2 to 0.6 mol/L, attributed to a gradually connected conductive circuit. As depicted in the figure, the curve becomes stable as the molar concentration of Py further increased from 0.6 to 1.0 mol/L. This result indicates that a complete connected conductive circuit can be formed when the Py molar concentration reaches 0.6 mol/L. Moreover, a gradually decreasing sheet resistance of PPy-coated cotton fabric was also observed with the increasing polymerization time from 60 to 150 min, while the resistance value has a slight increase as the processing time further increased to 180 min. The decreasing resistance reveals an improved electrical conductivity of the coated fabrics. What is more, the small standard deviation in the figures also indicates a uniformity of the sheet resistance of the fabrics.

Figure 6.

The sheet resistance of polypyrrole-coated cotton as a function of (a) the molar concentration of pyrrole (polymerization for 30 min) and (b) polymerization time (molar concentration of pyrrole at 0.6 mol/L).

Figure 7 illustrates the sheet resistance of Ag/PPy-coated cotton fabric as a function of sputtering time and power. The sheet resistance of the samples decreases after sputtering at different conditions, revealing that the combination of PPy and Ag films can improve the electrical conductivity of the cotton fabric. In addition, the sheet resistance of the samples decreases as the sputtering power increased from 100 to 150 W and then becomes stable as the power further increased from 150 to 300 W. Moreover, the sheet resistance of the samples decreases with increasing sputtering time from 10 to 25 min and then increased slightly with the time further increased to 30 min. As shown in Figure 7, the Ag/PPy-coated cotton fabric sputtered at 200 W for 25 min has the lowest average sheet resistance of 11.71 Ω/sq, which suggests that the highest electrical conductivity of the cotton fabric can be obtained. Moreover, the small standard deviation in figures indicates a uniformity of sheet resistance of the resultant fabric. The improving conductivity of cotton could be due to the formation of charge carriers (polarons and bipolarons) during the oxidative polymerization of PPy, which can create conductive paths.

Figure 7.

The sheet resistance of Ag/polypyrrole-coated cotton as a function of (a) sputtering time (sputtering power at 200 W) and (b) sputtering power (sputtering time for 10 min).

The conductive network formed by PPy and Ag particles is demonstrated in Figure 8. As shown in Figure 8, the PPy deposited first to make a basic conductive network. Although a conductive network can be formed when the PPy-coated cotton is prepared with the Py molar concentration of 0.6 mol/L and the polymerization time is 150 min, there were still many spaces that existed among the PPy because of the inherent surface roughness of the cotton fibers. In this case, a more complete conductive network can be further improved for a better electrical conductivity after the deposition of Ag thin film. Therefore, the evolution of electrical conductivity of the Ag/PPy-coated cotton can be explained by the following reasons: a basic perfect conductive network can be established after the fibers were pretreated with PPy, which acted as a relatively flat surface and can further contribute to form a better network by growing Ag thin film; an improved conductive network can be formed after sputtering with Ag particles, which not only grow on the fiber surface but also filled in the spaces between fibers and PPy chains. What is more, as shown in the Figure 9, the number of conductive paths for electrical charges can increase, leading to a high electrical conductivity when the PPy contacts with Ag particles, including inter- and intra-charge transfer among the PPy particles, inter- and intra-charge transfer among the Ag particles and inter-charge transfer between the PPy and Ag particles.⁴¹ This analysis is consistent with the electrical conductivity results (as shown in Figures 6 and 7).

Figure 8.

Schematic of conductive network formed by polypyrrole and Ag particles on cotton.

Figure 9.

Types of charge transfer between polypyrrole (PPy) and Ag: (A) intra-charge transfer between PPy chains; (B) intra-charge transfer between Ag particles; (C) inter-charge transfer between PPy and Ag; (D) inter-charge transfer between PPy chains.

Electromechanical performance

Figure 10 displays the relative resistance change (ΔR/R₀) of the PPy-coated cotton and Ag/PPy-coated cotton as a function of tensile strain, where R₀ represents the initial resistance and ΔR denotes the difference value between R₀ and real-time resistance (R). The electromechanical performance of the Ag/PPy-coated cotton after washing for 20 times is also studied, as depicted in Figure 10. As shown in the figure, the value of ΔR/R₀ referring to PPy-coated cotton and Ag/PPy-coated cotton is monotonously increased with the increasing loading strain ranging from 0% to 12.5%. The results reveal that the varying of the sheet resistance of the two fabrics is sensitive to the breaking elongation. A similar result was reported by Cai et al.³⁹ such that nylon/polyurethane (nylon/PU) fabric exhibited a high sensitivity after coating with reduced graphene oxide. There are few studies focused on the electromechanical performance of fabrics after washing. In our present study, the ΔR/R₀ of Ag/PPy-coated cotton decreases after washing 20 times under the same breaking elongation, and the result reveals that the sensitivity of the Ag/PPy-coated cotton decreases after washing for a long time. Therefore, the adhesion properties of the Ag/PPy-coated film and the cotton should be improved in further research.

Figure 10.

Relative resistance change (ΔR/R₀) as a function of the tensile strain of polypyrrole (PPy)-coated cotton, Ag/PPy-coated cotton and Ag/PPy-coated cotton after 20 washes. (The sample was conducted at 100 W, 10 min.)

The mechanism of the tensile strain on the resistance of the PPy-coated and the Ag/PPy-coated cottons is further analyzed. The deformation of the fabric structure under external forces can give rise to the dislocation between conductive particles and fibers/yarns, which leads to a variation of the conductive resistance of the fabric. According to Figure 10 and Equation (1),⁴² the Ag/PPy-coated cotton has a higher sensitivity coefficient than PPy-coated cotton when under the same tensile strain, which indicates that the Ag/PPy-coated cotton with a high sensitivity has a promising application in the preparation of smart wees for electrocardiogram signal acquisitarable textiles, such as flexible fabric electrodion

K = (Δ R / R_{0} / ɛ)

(1)

where K is the sensitivity coefficient and ε is the tensile strain.

Washing fastness

Tables 3 and 4 show the sheet resistance of Ag/PPy-coated cotton conducted at different sputtering power and sputtering time after various washing times. As shown in the tables, the value of the Ag/PPy-coated cotton increases as the washing time increased, which reveals a decreasing electrical conductivity because the current binding behavior among Ag, PPy and cotton is van der Waals forces. Although the sheet resistance of Ag/PPy-coated cottons is still high after washing, the resistance of the sample deposited at an optimal power of 300 W for 10 min is low at 2.21 kΩ/sq, even after 20 washes, and the resistance of the sample deposited at 200 W for an optimal time of 20 min is low at 3.58 kΩ/sq after 20 washes. However, these results indicate that the durability properties of the conductive fabrics should be further improved to meet the demands of practical use.

Table 3.

Sheet resistance (kΩ/sq) of Ag/polypyrrole-coated cotton deposited at different powers after washing (sputtering for 10 min)

Washing times	Sputtering power (W)
Washing times	100	150	200	250	300
0	0.050 ± 0.011	0.028 ± 0.013	0.027 ± 0.012	0.027 ± 0.009	0.026 ± 0.005
5	7.71 ± 1.5	3.18 ± 0.6	5.52 ± 1.3	2.19 ± 0.4	1.16 ± 0.2
10	8.93 ± 2.2	5.12 ± 1.3	5.52 ± 1.3	2.69 ± 0.8	1.92 ± 0.3
15	11.49 ± 2.2	7.34 ± 1.5	5.83 ± 1.2	3.33 ± 0.8	2.06 ± 0.3
20	12.85 ± 3.2	8.14 ± 1.9	6.01 ± 1.8	4.37 ± 1.5	2.21 ± 0.5

Table 4.

Sheet resistance (kΩ/sq) of Ag/polypyrrole-coated cotton deposited at different times after washing (sputtering at 200 W)

Washing times	Sputtering time (min)
Washing times	10	15	20	25	30
0	0.027 ± 0.012	0.021 ± 0.007	0.016 ± 0.006	0.012 ± 0.005	0.012 ± 0.003
5	3.18 ± 0.6	3.36 ± 0.74	1.22 ± 0.3	3.89 ± 1.4	5.29 ± 1.2
10	5.12 ± 1.3	3.93 ± 1.19	2.27 ± 0.8	8.91 ± 2.1	8.23 ± 2.7
15	7.34 ± 1.5	3.99 ± 0.77	2.51 ± 0.4	9.34 ± 1.4	12.31 ± 3.7
20	8.14 ± 1.9	5.18 ± 1.07	3.58 ± 0.5	10.73 ± 2.5	32.85 ± 7.1

Conclusions

In this study, highly electrical conductive cotton fabric is prepared by in situ polymerization followed by DC magnetron sputtering. The properties of the prepared conductive fabric as a function of polymerization and sputtering parameters are investigated. The electrical conductivity of cotton is increased after sputtering and the optimal sputtering parameter for good electrical conductivity of Ag/PPy-coated cotton fabric is conducted at 200 W for 25 min due to a complete formation of a conductive network of Ag/PPy on the cotton surface. The two-step method of in situ polymerization and magnetron sputtering proposed in this study opens a prompt pathway for the preparation of highly electrical conductive textiles. Moreover, the resultant Ag/PPy-coated cotton fabrics have promising applications in the development of electromagnetic shielding and antistatic and smart wearable textile products.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors gratefully acknowledge the financial support by Preparation and Properties of High Conductivity Flexible Graphene Composite Fabrics (Grant No. CS1809004).

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