Conductance-stable liquid metal sheath-core microfibers for stretchy smart fabrics and self-powered sensing

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Science Advances  28 May 2021:
Vol. 7, no. 22, eabg4041
DOI: 10.1126/sciadv.abg4041
  • Fig. 1 Preparation of LM sheath-core microfibers.

    (A) Schematic setup and the main components for the coaxial wet-spinning process for producing LM sheath-core microfibers. (B) A single as-spun fiber with the length of 380 m was collected on a continuously winding collector. (C) Microscopic images of LM sheath-core microfiber and human hair. (D) Photo of the microfiber threaded into a needle. (E) SEM image of the external surface of the microfiber. (F) SEM image of a knotted microfiber. (G) An LED can be lit up through a 55-cm-long activated LM sheath-core microfiber at a voltage of 3 V. (H) The cross-sectional SEM and corresponding elemental mapping images of the microfiber. Photo credit: Lijing Zheng, Donghua University.

  • Fig. 2 Mechanical properties and strain-insensitive conductance of LM sheath-core microfibers.

    (A) Tensile stress-strain curves of LM sheath-core microfibers and the hysteresis loops measured at increasing strains (stretching rate: 20 mm/min). (B) Cyclic loading-unloading curves at a fixed strain of 100% for 100 cycles (stretching rate: 20 mm/min; waiting time: 10 min). (C) Resistance changes of the stretch-induced conductivity activation of microfiber after freezing treatment. (D) Strain-dependent resistance changing rate of LM sheath-core microfibers with six different fluoroelastomer loadings [CPVDF-HFP-TFE = 0 (pure LM), 3, 5, 7, 9, and 11 wt %]. (E) Histogram of resistance change rates at fixed strains of different microfibers. (F) Comparison of the maximum strain, initial conductivity, and resistance change rate at 200% strain of LM sheath-core microfiber with other reported strain-insensitive and LM-based stretchable fiber conductors. (G) Resistance changes of the LM sheath-core microfiber over 600 cycles between 0 and 100% strain. (H to J) Resistance changes of the microfiber upon pressing, twisting, and bending.

  • Fig. 3 Mechanism of the strain-insensitive conductance of LM sheath-core microfibers.

    (A) Photographs of EGaIn droplet surface reconciliation on PVDF-HFP-TFE film during stretching and releasing. (B) Schematic illustration of the surface creation and readjustment of EGaIn on the PVDF-HFP-TFE film through the dipole-dipole interactions between Ga2O3 layer and polar C-F groups. (C) Ga 3d XPS spectrum of LM particles. a.u., arbitrary units. (D) Attenuated total reflection–Fourier transform infrared (ATR-FTIR) spectra of PVDF-HFP-TFE and PVDF-HFP-TFE/LM composite (CPVDF-HFP-TFE = 7 wt %) in the C-F stretching region. (E) Polarizing micrographs of the LM sheath-core microfiber during stretching observed in the reflection mode. (F) 2D SAXS patterns and scattering intensity plots against q (the integration area is the selected rectangular area) of the microfiber at strains of 0 and 300%, respectively. (G) SAXS azimuth integration and corresponding Lorentz fitting curve. The inset picture is the 2D image of the fiber at 300% strain. Photo credit: Lijing Zheng, Donghua University.

  • Fig. 4 Joule heating properties of LM sheath-core microfibers.

    (A) The stepwise temperature changing curve and corresponding infrared thermal images of the LM sheath-core microfiber with the applied voltage from 0 to 1.2 V. (B) Cyclic stability test of the joule heating performance of the microfiber by switching voltage between 0 and 0.8 V. (C) The enlarged image of the dashed area in (B) shows the temperature changes in one on-off cycle. (D) Infrared thermal images of the fiber embedded in an elastic fabric glove (applied voltage, 0.4 V) as the fingers bend. (E) Microscopic images of the electrothermochromic microfibers and photographs of the fibers embedded in a fabric by switching the voltage on and off. Photo credit: Lijing Zheng, Donghua University.

  • Fig. 5 Application of the LM sheath-core microfibers/fabrics in self-powered sensors.

    (A) Working mechanism of LM sheath-core microfiber-based self-powered sensor. (B) Comparison of the Young’s moduli and relative triboelectric polarities of common triboelectric materials. (C) Voltage signals generated by contacting LM microfiber with five different triboelectric materials at the motion frequency of 2 Hz. The length of the fiber is 4 cm. (D) Voltage signals under different frequencies generated by contacting the fiber with silk. (E) Voltage signals under different strain levels of the fiber at the motion frequency of 2 Hz. The length of the fiber is 1 cm. (F) Photos and corresponding voltage signals by bending the fiber sensor–embedded spandex glove worn on a prosthetic hand. (G) Photos and corresponding voltage signals of the fiber sensor adhered to a human wrist. Photo credit: Lijing Zheng, Donghua University.

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