Machine-Washable Conductive Silk Yarns with a Composite Coating of Ag Nanowires and PEDOT:PSS

Abstract

Electrically conducting fibers and yarns are critical components of future wearable electronic textile (e-textile) devices such as sensors, antennae, information processors, and energy harvesters. To achieve reliable wearable devices, the development of robust yarns with a high conductivity and excellent washability is urgently needed. In the present study, highly conductive and machine-washable silk yarns were developed utilizing a Ag nanowire and PEDOT:PSS composite coating. Ag nanowires were coated on the silk yarn via a dip-coating process followed by coating with the conjugated polymer:polyelectrolyte complex PEDOT:PSS. The PEDOT:PSS covered the Ag nanowire layers while electrostatically binding to the silk, which significantly improved the robustness of the yarn as compared with the Ag nanowire-coated reference yarns. The fabricated conductive silk yarns had an excellent bulk conductivity of up to ∼320 S/cm, which is largely retained even after several cycles of machine washing. To demonstrate that these yarns can be incorporated into e-textiles, the conductive yarns were used to construct an all-textile out-of-plane thermoelectric device and a Joule heating element in a woven heating fabric.

Keywords: Ag nanowire; PEDOT:PSS; conductive silk yarn; nanocomposite; washing machine proof.

Figure 1

(a) Schematic and description of the preparation of conductive silk yarns with an Ag nanowire/PEDOT:PSS composite coating. (b) Top view and (c, d) cross-sectional SEM images of individual filaments that make up the conductive silk yarns.

Figure 2

(a) Electrical conductivity of silk yarns as a function of the number of dip-coating cycles in the Ag nanowire solution. (b) Normalized conductivity of the silk yarns after (black) two, (red) three, and (blue) four dipping cycles as a function of the 180 °C postannealing time. σ₀ indicates the initial conductivity before annealing. (c) Conductivity of the silk yarns as a function of the number of dip-coating cycles in Ag nanowire solutions of different concentrations.

Figure 3

Normalized resistance change of silk yarns with Ag nanowire and Ag nanowire/PEDOT:PSS coatings as a function of (a) number of machine-washing cycles, and (b) number of bending cycles. (c) Stress–strain curves of the silk yarns with the composite coating of Ag nanowire and PEDOT:PSS (solid lines) and the change in normalized resistance measured during tensile tests (symbols). R₀ is the initial resistance before testing, and R is the resistance measured under washing/bending/tensile tests.

Figure 4

Schematics of (a) a thermocouple and (b) its equivalent electric circuit. (c) Electrical measurement of a thermoelectric textile consisting of a single thermocouple, with the open circuit voltage, V_oc, as a function of ΔT, and the power output as a function of the measured current at ΔT = 70 K. Insets are top and side view photographs of the out-of-plane thermoelectric device with one n-type leg composed of the Ag nanowire/PEDOT:PSS-coated silk yarn and one p-type leg composed of the PEDOT:PSS-only coated silk yarn.

Figure 5

(a) Photograph of woven heating fabric using the Ag nanowire/PEDOT:PSS-coated conductive silk yarn as a Joule heating element, and IR camera images of the heating fabric when applying (b) no voltage, (c) 2 V, and (d) 3 V. The respective IR images were taken no more than 30 s after the voltage was switched on.