Applicability of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) impregnated polyurethane nanoweb as a transmission line for smart textiles

Abstract

Smart clothing, which can be manufactured based on smart textiles with electrical conductivity, can be used as a transmission line to transmit signals. The performance of the fabricated textile-based transmission line can be determined by evaluating light-emitting diode consistency. In this study, a textile-based transmission line was fabricated by impregnating two concentrations of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) to impart the electrical conductivity to a polyurethane (PU) nanoweb. Three conditions of thermal treatment were conducted to decrease the electrical resistance, and the thickness, electrical, surface, and chemical properties were evaluated. The thickness of the specimens tended to decrease at the low concentration, and the thermal treatment temperature increased. The linear resistances decreased from 1580 Ω/cm (PA) to 310.6 Ω/cm (PB120) as the concentration of PEDOT: PSS and thermal treatment temperature increased. Field emission scanning electron microscope images show that the PU nanoweb was uniformly and successfully impregnated with PEDOT: PSS. Raman spectra indicate an effect of the thermal treatment on the structural change of the PEDOT chains, which suggests an electrical resistance change of specimens. As a result, the optimum concentration of the PEDOT: PSS impregnated PU nanoweb as a transmission line for smart textiles is 2.6 wt%, and the thermal treatment temperature is 120℃. The performance of the textile-based transmission line (PB120) according to the length was higher as the length of the specimen was shorter. The highest consistency was 51 lm/m² (50 mm), and the lowest was 45 lm/m² (150 mm). Therefore, the PEDOT: PSS/PU nanoweb has applicability and feasibility as a transmission line.

Keywords

poly(3 4-ethylenedioxythiophene): poly(styrene sulfonate)polyurethane nanoweb transmission line smart textiles

The Internet of Things (IoT), meaning all things connect to the internet, is currently realizing the benefits of the data economy in numerous industries, such as healthcare, manufacturing, emergency management or defense, and public safety.^1,2 The IoT has enabled the development of high value-added smart clothing based on its technological convergence with textiles.^2,3 Also, due to the development of fifth-generation (5 G) communication networks, smart clothing builds a hyper-connected society by connecting and interacting with things-to-things, human-to-things, and human-to-human.^3,4 That is paving the way to the novel paradigm of the ‘Internet of Smart Clothing.’⁴ Smart clothing, which can be manufactured based on smart textiles with electrical conductivity, is being developed to monitor human body parameters and can be used as a circuit to transmit signals.^5,6 It can be applied as a layered clothing with a sandwich structure without being affected by the environment. It can provide the convenience and safety of the wearer and increase activity, especially for wearers working in harsh environments.^5,7 However, most of the smart clothing products currently on the market are developed as ‘on-cloth’ with electronic devices attached.⁸ Textile-based research and development are essential for ‘in-cloth’ smart clothing with excellent comfort and performance.^7,9,10

Previous research on the fabrication of smart textiles has used nanoscale metals, graphene, carbon nanotubes, and intrinsically conductive polymers (ICPs) to impart electrical conductivity to textiles.^11–14 These conductive materials were applied to textiles by coating, ink-jet printing, or electrospinning using polymer solutions.^15–17 In this study, poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) was used to impart electrical conductivity to nanowebs by impregnation. The impregnation method was suitable for the PEDOT: PSS dispersion applied to textiles.¹⁷ PEDOT: PSS, one of the ICPs, is considered a promising material for smart textiles due to its superior advantages, such as water-solubility, high mechanical flexibility, and excellent environmental stability.^17,18 Also, thermal treatment to PEDOT: PSS can effectively reduce the electrical resistivity in a short time.¹⁸ This is a more straightforward and more economical method than that of using PEDOT: PSS compounded with other polymeric materials.¹⁹

When developing smart textiles, high electrical conductivity, wearability, and flexibility should be considered.^20,21 Among the various advanced materials, nanowebs are suitable to meet these requirements due to their form and structure.²¹ Nanowebs consist of randomly positioned nanofibers and have many advantages, such as large specific surface areas and the tremendous number of pores due to their nanosized diameters.^22–24 Because of these structural characteristics, nanowebs impregnated into conductive materials can impart electrical conductivity, and this is a simple method to fabricate smart textiles.^24,25 Also, since the impregnation method does not affect the characteristics of nanowebs, it can still be used for flexible and deformable applications.¹⁹ When thermal treatment is performed on nanowebs, the nanofibers are fused by heat to form an interconnected network structure and are effective in stabilizing the shape of the nanofibers.²⁶ In this study, a polyurethane (PU) nanoweb was used as the base fabric because PU has outstanding flexibility and stretchability.

This study aimed to investigate the optimum treatment conditions of impregnating the PU nanoweb in PEDOT: PSS to produce a transmission line for developing smart textiles. Two concentrations of PEDOT: PSS and three thermal treatment temperatures were compared. The thickness and electrical resistance of the specimens were measured. The surface characteristics and chemical properties of the specimens were evaluated. Also, to confirm the applicability of the transmission line, the consistency of the PEDOT: PSS/PU nanoweb transmission line connected with a light-emitting diode (LED) lamp was measured.

Experimental details

Materials

Commercially available PU nanoweb manufactured by centrifugal spinning was purchased from Pardam, Nanotechnology, s.r.o. (Roudnice nad Labem, Czech Republic). The fiber diameter ranged from 400 to 800 nm, the weight was 13 g/m², and the sheet electrical resistance was 1 × 10¹¹ Ω/sq. PEDOT: PSS aqueous dispersion (1.3 wt%) was purchased from Sigma-Aldrich, USA. The composition of PEDOT was 0.5 wt%, that of PSS was 0.8 wt%, and the conductivity was 1 S/cm (Table 1). To increase its concentration, 25 ml of 1.3 wt% PEDOT: PSS dispersion was put in a beaker and evaporated with water at 100℃ for 1 hour using a hot plate and magnetic stirrer (MS-300HS, Misung Scientific Co., Ltd). The obtained PEDOT: PSS dispersion had a concentration of ca. 2.6 wt% as estimated by weight change. Table 1 summarizes the characteristics of the PU nanoweb and PEDOT: PSS used.

Table 1.

Characteristics of the polyurethane (PU) nanoweb and the poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS)

PU nanoweb	Fiber structure	Randomly oriented
	Fiber diameter	400–800 nm
	Fiber length	Continuous^a
	Thickness	20,000 nm
	Web area density	13 g/m²
	Melting point	138℃
	Sheet resistance	1 × 10¹¹ Ω/sq
PEDOT: PSS	Concentration	1.3 wt% dispersion in H₂O
	Composition	PEDOT content 0.5 wt% PSS content 0.8 wt%
	Conductivity	1 S/cm

The fiber length is one of the specifications received from the manufacturer. The manufactured nanofibers form a continuous length, which is the basic structure of the fiber, such as common filament fibers.

Impregnation methods

Eight PU nanowebs cut into 50 mm × 50 mm were impregnated with 0.5 g of the 1.3 wt% or 2.6 wt% PEDOT: PSS dispersion for 15 minutes (Figure 1). Then two of the specimens were dried entirely at room temperature (21 ± 1℃) for 24 hours. The other specimens were treated at 80℃, 100℃, and 120℃, respectively, for 15 minutes using a vacuum drying oven (VISIONBIONEX, Republic of Korea). Preliminary experiments confirmed that the specimens were dried entirely at room temperature (21 ± 1℃) for 24 hours. During the thermal treatment, the drying time was set at 15 minutes because the specimens did not dry completely at 10 minutes and shrunk at 20 minutes. Also, preliminary experiments showed that the PEDOT: PSS impregnated PU nanoweb melted above 130℃ because the melting point of the PU nanoweb was 138℃. All experiments were conducted under the standard laboratory environmental conditions of 21 ± 1℃, and 65 ± 2% relative humidity (RH) (ASTM D1776²⁷).

Figure 1.

Schematic illustrations of the poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) impregnated polyurethane (PU) nanoweb.

Thickness

The thickness of the specimen was measured by a field emission scanning electron microscope (FE-SEM, 7610F-Plus, JEOL Ltd). Nine arbitrarily selected specimens were cut into 10 mm × 10 mm, and the thickness of the specimens was adjusted to an appropriate magnification to observe the cross-sectional images of the nanoweb by the FE-SEM. Because the thicknesses of the PU nanoweb were not uniform due to their manufacturing processes, each specimen was measured three times in different areas to calculate the mean value.

Electrical properties

Linear resistance (Ω/cm) and sheet resistance (Ω/sq) were measured. The linear resistance of the impregnated specimens was measured using a digital multimeter (DONGHWA DM1010, Republic of Korea). A four-point probe-type surface resistivity meter (CMT-SR1000N, Republic of Korea) was used to measure the sheet resistance. The impregnated specimens were cut into 30 mm × 30 mm squares and measured five times to calculate the mean value. The average value of sheet resistance was calculated and converted into the specific resistance (Ω·cm). The specific resistance quantifies the amount of material current flow, and it is the inversed value of the conductivity. The specific resistivity is the intrinsic resistance value of the material. The resistance value of the pure material was known. However, the value of the mixture material can be obtained by calculation. In this case, the specific resistance value was calculated according to the following formula²⁸

\begin{matrix} Specificresistance (Ω \cdot cm) = Sheetresistance (Ω / sq) \\ \times Specimenthickness (cm) \end{matrix}

Surface properties

A FE-SEM (7610F-Plus, JEOL Ltd) was used to observe the morphology and the surface microstructure of the specimens. The surface property changes of the specimens after PEDOT: PSS impregnation and heat treatment were investigated.

Chemical properties

Raman spectra (LabRam Aramis, Horiba) were used to confirm the chemical structural changes of the specimens. Raman spectra were collected by the shift range from 1000 to 2000 cm^–1 using 532 nm lasers.

Fabrication of the PEDOT: PSS/PU nanoweb transmission line

The specimen showing the lowest electrical resistance was used to fabricate the PEDOT: PSS/PU nanoweb transmission lines. The LED circuit was constructed on a breadboard according to the electrical circuit diagrams, and the functionality of the design was verified (Figure 2). A breadboard, three-wire switch, LED lamp, copper wire, resistance, and AA battery were used. After ascertaining the operation of the circuit, the specimen was cut to 10 mm × 10 mm and attached by alligator clips to confirm the applicability of the transmission line. After preliminary testing, the transmission line was fabricated with specimens of 10 mm × 50 mm, 10 mm × 100 mm, and 10 mm ×150 mm size to evaluate the performance according to length.

Figure 2.

Electrical network diagram of the light-emitting diode circuit.

Figure 3.

Measurement of light-emitting diode consistency (lm/m²).

LED consistency properties

A luxmeter (ST-126, Sincon) was used to measure the consistency (lm/m²) of the LED lamp. The consistency of all the specimens was measured three times to calculate the average consistency value. A wooden case of 200mm x 200mm x 200 mm in size was made to minimize the effect of external illumination (Figure 3). The top and bottom sides of the wooden case were removed and covered with black PU fabrics to prevent external illumination.

Statistical analyses

An analysis of variance (ANOVA) was performed to establish the relationship among the thermal treatment temperature (X₁) and the concentration of PEDOT: PSS dispersion (X₂) as independent variables, and the thickness and the electrical resistance (Y) as the dependent variables. All statistical analyses were performed by IBM SPSS statistics software (version 25.0).²⁹

Results and discussion

Thickness

The specimen thicknesses were used to determine the change of thickness of the specimens according to the concentration PEDOT: PSS dispersion and thermal treatment temperature. The average thickness of the untreated PU nanoweb was approximately 25 µm (Table 2). The thickness of the impregnated specimens tended to increase with a high concentration of PEDOT: PSS. All specimens impregnated with 2.6 wt% PEDOT: PSS were thicker than those impregnated with 1.3 wt% PEDOT: PSS. The higher the thermal treatment, the lower the thickness of the impregnated specimens. When thermal treatment was performed at high temperatures, the stress among the PU nanofiber and micropore space of the nanoweb was reduced. It can be inferred that the PEDOT: PSS has completely penetrated the PU nanoweb and the surface of the PU nanoweb. As a result, a decrease in the thickness of the specimens may have caused a reduction in the electrical resistance of the specimens.

Table 2.

Thickness changes of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) impregnated polyurethane nanoweb

Concentration (wt%)	Specimens	Thickness ± SD (µm)
Untreated	UT	25 ± 3.55
1.3	PA	20.7 ± 2.59
	PA80	10.9 ± 3.17
	PA100	6.47 ± 0.39
	PA120	5.23 ± 0.02
2.6	PB	24.9 ± 0.33
	PB80	13.9 ± 0.78
	PB100	8.33 ± 1.08
	PB120	6.47 ± 0.28

PA: 1.3 wt% PEDOT: PSS; PA80: 1.3 wt% PEDOT: PSS, 80℃; PA100: 1.3 wt% PEDOT: PSS, 100℃; PA120: 1.3 wt% PEDOT: PSS, 120℃; PB: 2.6 wt% PEDOT: PSS; PB80: 2.6 wt% PEDOT: PSS, 80℃; PB100: 2.6 wt% PEDOT: PSS, 100℃; PB120: 2.6 wt% PEDOT: PSS, 120℃; SD: Standard deviation.

Figure 4 shows that the thickness (Y) of specimens was reduced as the thermal treatment temperature (X₁) increased and the concentration of PEDOT: PSS dispersion (X₂) decreased. The ANOVA results found significant differences in thickness depending on the thermal treatment temperature (F-value = 99.81, df = 3, p < .001) as well as the concentration of PEDOT: PSS dispersion (F-value = 11.07, df = 1, p < .01). The result implied that the thickness (Y) was significantly affected by the thermal treatment temperature (X₁) and the concentration of PEDOT: PSS dispersion (X₂).

Figure 4.

Interaction plot among the thermal treatment temperature (X₁), the concentration of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) dispersion (X₂), and the thickness (Y).

Electrical resistance and electrical conductivity

The electrical resistances (linear resistance (Ω/cm), sheet resistance (Ω/sq), and specific resistance (Ω·cm)) of the impregnated specimens are shown in Table 3. Figure 5 shows that the electrical resistance of the specimens decreased as the concentration of PEDOT: PSS dispersion and thermal treatment temperature increased. The linear resistance value was 1580 Ω/cm when PEDOT: PSS impregnated PU nanoweb of 1.3 wt% was dried at room temperature (21 ± 1℃), and it decreased to approximately 310.6 Ω/cm after using a higher concentration of PEDOT: PSS (2.6 wt%) and higher temperature (120℃) for thermal treatment. Also, the sheet resistance value of the specimens decreased from 779.3 to 232.9 Ω/sq. The specific resistance value was gradually reduced as the concentration of PEDOT: PSS and thermal treatment temperature increased. The specific resistance value of specimens was about approximately 1.90 Ω·cm before the thermal treatment of the 1.3 wt% PEDOT: PSS impregnated PU nanoweb. However, it decreased to 0.15 Ω·cm after the thermal treatment of the 2.6 wt% PEDOT: PSS impregnated PU nanoweb. Figure 6(a) shows that the linear resistance (Y) of specimens was reduced as the thermal treatment temperature (X₁) and the concentration of PEDOT: PSS dispersion (X₂) increased. The ANOVA results found significant differences in linear resistance depending on the thermal treatment temperature (F-value = 137.29, df = 3, p < .001), as well as the concentration of PEDOT: PSS dispersion (F-value = 73.23, df = 1, p < .001). Figure 6(b) shows that the sheet resistance (Y) of specimens was also reduced as the thermal treatment temperature (X₁) and the concentration of PEDOT: PSS dispersion (X₂) increased. The ANOVA results found significant differences in sheet resistance depending on the thermal treatment temperature (F-value = 94.51, df = 3, p < .001), as well as the concentration of PEDOT: PSS dispersion (F-value = 64.46, df = 1, p < .001). These results implied that the electrical resistance (Y) was significantly affected by the thermal treatment temperature (X₁) and the concentration of PEDOT: PSS dispersion (X₂).

Figure 5.

Electrical resistance of the specimens: (a) 1.3 wt% poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS); (b) 2.6 wt% PEDOT: PSS.

Figure 6.

Interaction plot among the thermal treatment temperature (X₁), the concentration of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) dispersion (X₂), and the electrical resistance (Y): (a) linear resistance (Ω/cm); (b) sheet resistance (Ω/sq).

Table 3.

Electrical resistance and electrical conductivity of the poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) impregnated polyurethane nanoweb

	Electrical resistance
Specimens	Linear resistance ± SD (Ω/cm)	Sheet resistance ± SD (Ω/sq)	Specific resistance (Ω·cm)	Electrical conductivity (S/cm)
PA	1580 ± 135.5	779.3 ± 61.2	1.90	0.53
PA80	990.6 ± 19.2	659.4 ± 30.9	0.82	1.22
PA100	752.2 ± 88.7	469.1 ± 50.7	0.28	3.61
PA120	486 ± 25.5	345 ± 50.2	0.18	5.56
PB	1042 ± 141	625.2 ± 94	1.57	0.64
PB80	784.8 ± 149.9	470.9 ± 78.9	0.66	1.52
PB100	534.6 ± 125.5	320.8 ± 47.1	0.27	3.74
PB120	310.6 ± 53.7	232.9 ± 32.6	0.15	6.64

The electrical conductivity value is the inverse of the specific resistance value, and the material electrical conductivity value indicates the strength of the electrical current flow. The electrical conductivity value was improved from approximately 0.53 to 6.64 S/cm. These results showed that the lower the electrical resistance, the higher the electrical conductivity. According to previous research,³⁰ if the electrical resistance value is high (10⁵–10⁸ Ω·cm), it can be used as an antistatic textile. When the electrical resistance value is in the middle of 10²–10⁵ Ω·cm, it can be used as conductive coveralls for workers in electric power corporations to prevent electrostatic induction. When the electrical resistance is low, in the range of 10^–1–10¹ Ω·cm, it is suitable for use in smart textiles, particularly as a transmission line for smart clothing. Also, the electrical resistance value of the graphene-coated PU nanoweb transmission line was approximately 10^–1 Ω·cm.¹³ In this study, all samples have low electrical resistance values of 10^–1–10¹ Ω·cm; accordingly, it is predicted that the electrical properties of the PEDOT: PSS impregnated PU nanoweb make it suitable for use in the signal transmission lines of smart clothing.

These results indicate that thermal treatment reduces the electrical resistance of the specimens. The temperature-dependent behavior of PEDOT: PSS originates from the microstructure of the polymer material.³¹ PEDOT: PSS forms so-called core–shell structured grains in which the core of the grain is a PEDOT nanocrystal, and a PSS-rich shell surrounds the core.³² The insulating PSS boundaries have a significant effect on the overall resistivity of PEDOT: PSS. The co-adhesion between PSS chains results from the hydrogen bonding between the intermolecular or intramolecular PSS chains. When heat is applied to increase the concentration of PEODT: PSS, the water molecules evaporate. This could weaken the hydrogen bond between the water molecules and the PSS chains or intramolecular PSS chains. Therefore, at high temperatures, the total number of PSS particle boundaries is smaller, and the effective ‘size’ of the boundaries is reduced, which reduces the resistance.³³

Figure 7 shows that the electrical resistance value decreased when the PEDOT: PSS impregnated PU nanoweb thickness decreased. All specimens impregnated with 2.6 wt% PEDOT: PSS were thicker than those impregnated with 1.3 wt% PEDOT: PSS; therefore, the electrical resistance value was lower due to differences in concentration of PEDOT: PSS.

Figure 7.

Electrical resistances of the specimens according to thickness: (a) 1.3 wt% poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS); (b) 2.6 wt% PEDOT: PSS.

Field emission scanning electron microscope

The surface property of the PU nanoweb was analyzed by a FE-SEM. The untreated PU nanoweb is shown in Figure 8(a), where countless nanofiber strands were randomly entangled. According to the FE-SEM results, it was found that the PEDOT: PSS dispersion was completely impregnated inside as well as on the surface of the specimens. In other words, the impregnation method showed that the PEDOT: PSS dispersion successfully imparted electrical conductivity to the specimens. Figures 8(b) and (f) show the PEDOT: PSS impregnated PU nanoweb without thermal treatment. Figure 8(b) shows PA (1.3 wt% PEDOT: PSS) and Figure 8(f) shows PB (2.6 wt% PEDOT: PSS), the surfaces of which both had some irregularities. In Figure 8(f), the PU nanofiber strands appeared on the surface, but the PEDOT: PSS dispersion was comparatively more uniform than that in Figure 8(b). The strands were mostly covered with PEDOT: PSS dispersion. Moreover, the surface uniformity increased with thermal treatment. Figures 8(c) and (g) show thermal treatment at 80℃, Figures 8(d) and (h) show thermal treatment at 100℃, and Figures 8(e) and (i) show thermal treatment at 120℃. A few nanofibers were exposed, and the surface was relatively uniform when thermal treatment temperature increased. In particular, Figure 8(i) shows that the surface was evenly covered with the PEDOT: PSS dispersion. These results confirm that the high concentration and thermal treatment create a uniform surface of the PEDOT: PSS impregnated PU nanoweb.

Figure 8.

Field emission scanning electron microscope (×1000) images of polyurethane nanofiber webs: (a) untreated; (b) PA (1.3 wt% poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS)); (c) PA80 (1.3 wt% PEDOT: PSS, 80℃); (d) PA100 (1.3 wt% PEDOT: PSS, 100℃); (e) PA120 (1.3 wt% PEDOT: PSS, 120℃); (f) PB (2.6 wt% PEDOT: PSS); (g) PB80 (2.6 wt% PEDOT: PSS, 80℃); (h) PB100 (2.6 wt% PEDOT: PSS, 100℃); (i) PB120 (2.6 wt% PEDOT: PSS, 120℃).

Raman spectra

Chemical analysis of the specimens was performed by Raman spectra. Figure 9 shows the spectrum of the specimens. Raman spectra of all specimens revealed the C_α–C_α inter-ring stretching vibration at 1256 and 1360 cm^–1. Furthermore, the spectrum also showed C_α = C_β symmetric stretching at 1440 cm^–1, and C_α = C_β asymmetric stretching at 1500–1570 cm^–1. After the thermal treatment, Figure 9(a) shows that the symmetric vibration peak of the thiophene ring slightly shifted from 1441 to 1438 cm^–1. Figure 9(b) shows that the symmetric vibration peak of the thiophene ring slightly shifted from 1436 to 1433 cm^–1. It can be inferred that the benzoid (C_α = C_β) structure present in the specimens had been transformed into a quinoid (C_α-C_β) structure after the thermal treatment. Because of the conductivity of PEDOT: PSS attributed to a carbon single bond structure of PEDOT, the slight shifting would have affected the reduction of the electrical resistance of the specimens.

Figure 9.

Raman spectra of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) impregnated polyurethane nanoweb: (a) 1.3 wt% PEDOT: PSS; (b) 2.6 wt% PEDOT: PSS.

Figure 10.

(a) Light-emitting diode (LED) ON/OFF according to switch operation. (b) LED ON/OFF according to switch operation connected with the poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) impregnated polyurethane nanoweb.

LED circuit

PB120 showed the lowest electrical resistance and was used to fabricate the transmission lines. A LED circuit was utilized to test the applicability of the PEDOT: PSS impregnated PU nanoweb as an interconnect for power and signal transmission. Figure 10(a) shows that the LED circuit was constructed on a breadboard and was operated according to the switch. As shown in Figure 10(b), the copper wire in the LED circuit was successfully substituted by the PEDOT: PSS impregnated PU nanoweb using alligator clips. Table 4 shows the consistency (lm/m²) of the LED lamp connected with the PEDOT: PSS impregnated PU nanoweb compared to copper wire. The consistency value of the specimens became slightly higher when the length of the PEDOT: PSS/PU nanoweb shortened. The results confirmed that the performance of the PEDOT: PSS/PU nanoweb transmission line was inferior to that of the copper wire, but the LED circuit worked successfully. Therefore, the PEDOT: PSS/PU nanoweb can be applied as a transmission line for smart textiles. The results indicate that when it had an electrical resistance of approximately 10^–1 Ω·cm, the nanoweb-based smart textile could perform as a transmission line properly with stable and good quality signals.

Table 4.

Consistency (lm/m²) of the LED lamp connected with PEDOT: PSS impregnated PU nanoweb

Specimens	Size (mm)	Consistency ± SD (lm/m²)
PB120	10 × 50	51 ± 6.6
	10 × 100	48 ± 5.3
	10 × 150	45 ± 2.6
Copper wire	10 × 50	172 ± 7.5
	10 × 100	168 ± 5.2
	10 × 150	165 ± 13

PB120: 2.6 wt% poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate), 120℃; SD: Standard deviation.

Conclusion

This study introduced simple methods to fabricate smart textiles based on a PU nanoweb. It investigated the characteristics of the specimens to explore their applicability as a transmission line for smart clothing. The electrical conductivity of the PEDOT: PSS impregnated PU nanoweb is higher than that of the PEDOT: PSS/d-sorbitol impregnated PU fabric with 10 repeated dipping cycles.²⁵ In the case of impregnating with PEDOT: PSS, the electrical conductivity values of the PU nanoweb were about 0.5–6.6 S/cm and the electrical conductivity values of the PEDOT: PSS/d-sorbitol impregnated PU fabric were approximately 0.1–1.7 S/cm. The thermal treatment on the PEDOT: PSS impregnated PU nanoweb is a more straightforward method with which to enhance the electrical conductivity than that of mixing PEDOT: PSS with other polymer materials or repeated dipping cycles. The LED circuit for evaluating the performance of the PEDOT: PSS/PU nanoweb transmission line worked successfully. The LED circuit of the graphene-coated PU nanoweb transmission line was developed by Jang and Cho.¹³ However, the LED circuit with thermoplastic polyurethane (TPU) seam sealing tape attached cannot be reconstructed again, and it is also difficult to replace the electronic device. In this study, the LED circuit of the PEDOT: PSS impregnated PU nanoweb transmission line has the advantage that the electronic device can be easily replaced and used many times. In addition, durability/cleaning to abrasion is required because environmental influences such as twisting and bending can change the electrical properties and performance of the textile-based transmission line.³⁴ Textile-based transmission lines can be applied as a layered fabric with a sandwich structure without being affected by the environment. It could be applied especially for firefighters, soldiers, and night workers to provide convenience and the safety of the wearer from risk factors in the dark and to increase activity.

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: This work was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. NRF-2019R1F1A1060955) and also supported (in part) by the Brain Korea 21 Plus Project of Department of Clothing and Textiles, Yonsei University, in 2020.

ORCID iDs

Hyeon-seon Cho

Eunji Jang

Hang Liu

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