Super Tough and Spontaneous Water-Assisted Autonomous Self-Healing Elastomer for Underwater Wearable Electronics

Abstract

Self-healing soft electronic material composition is crucial to sustain the device long-term durability. The fabrication of self-healing soft electronics exposed to high moisture environment is a significant challenge that has yet to be fully achieved. This paper presents the novel concept of a water-assisted room-temperature autonomous self-healing mechanism based on synergistically dynamic covalent Schiff-based imine bonds with hydrogen bonds. The supramolecular water-assisted self-healing polymer (WASHP) films possess rapid self-healing kinetic behavior and high stretchability due to a reversible dissociation-association process. In comparison with the pristine room-temperature self-healing polymer, the WASHP demonstrates favorable mechanical performance at room temperature and a short self-healing time of 1 h; furthermore, it achieves a tensile strain of 9050%, self-healing efficiency of 95%, and toughness of 144.2 MJ m^-3 . As a proof of concept, a versatile WASHP-based light-emitting touch-responsive device (WASHP-LETD) and perovskite quantum dot (PeQD)-based white LED backlight are designed. The WASHP-LETD has favorable mechanical deformation performance under pressure, bending, and strain, whereas the WASHP-PeQDs exhibit outstanding long-term stability even over a period exceeding one year in a boiling water environment. This paper provides a mechanically robust approach for producing eco-friendly, economical, and waterproof e-skin device components.

Keywords: flexible wearable devices; light-emitting diodes; perovskite quantum dots; underwater electronics; water-insensitive self-healing elastomers.

Figure 1

Molecular architecture of PDMS‐MDI _x ‐TFB_{1− x} elastomer with eco‐friendly, high toughness, stretchability, and autonomous self‐healing property. a) Synthetic route to prepare PDMS‐MDI _x ‐TFB_{1− x} self‐healing elastomer. b) Schematic illustration of ideal structure of PDMS‐MDI _x ‐TFB_{1− x} based on the synergistic effect of reversible weaker imine bonds and stronger hydrogen bonds. c) ¹H NMR spectrum of PDMS‐MDI_0.4‐TFB_0.6 elastomer. d) In situ ATR‐FTIR spectra of PDMS‐MDI_0.4‐TFB_0.6 upon heating from 30 to 170 °C. 1660–1620 cm⁻¹ (left), 1600–1520 cm⁻¹ (right).

Figure 2

Mechanical and self‐healing properties of PDMS‐MDI _x ‐TFB_{1− x} elastomer film. a) Photographs of PDMS‐MDI_0.2‐TFB_0.8 film before stretching (left) and stretch to a strain of 5300% (right). b) Stress–strain curves of PDMS‐MDI _x ‐TFB_{1− x} elastomer with different ratios with a sample width of 10 mm, a thickness of 0.5 mm, and a length of 30 mm at a loading rate of 20 mm min⁻¹. c) A notched‐insensitive alongside highly stretchable elastomer of PDMS‐MDI_0.4‐TFB_0.6 before stretching (left) and after 2300% stretching (right). The inset figure is the schematic diagram of notch location (0.5 mm in length). d) Stress–strain of the unnotched and notched PDMS‐MDI_0.4‐TFB_0.6 elastomer with a length of 30 mm at a loading rate of 20 mm min⁻¹. e,f) Stress–strain curves of the PDMS‐MDI_0.4‐TFB_0.6 film healed for different time at room temperature (rt), showing that stretching ability increased is associated with the extended healing time. The optical microscope image (8 × 5 mm) (left) of PDMS‐MDI_0.4‐TFB_0.6 before damaged and after self‐healing 4 h at rt. g) Stress–‐strain curve of PDMS‐MDI_0.4‐TFB_0.6 film in cyclic stress–strain tests (40% strain). h) Recovery ratio and residual strain of PDMS‐MDI_0.4‐TFB_0.6 film before and after healed in cyclic stress–strain tests.

Figure 3

Schematic diagrams of water‐assisted self‐healing mechanism of PDMS‐MDI _x ‐TFB_{1− x} elastomer film. a) Illustration of reversible imine bonds and dynamic hydrogen bonds dissociation–association with water molecules upon underwater healing process. b–d) Illustration of chain motion and water‐intake following crack propagation, the chain motion within the damaged area expend, and water is getting expulsed, thereby reforming the H‐bond and covalent imine bond upon self‐healing film. e) Photographs of PDMS‐MDI_0.4‐TFB_0.6 film before stretching (left) and stretch to a strain of 9050% (right) after underwater healing process. f) Stress–strain curves of the PDMS‐MDI_0.4‐TFB_0.6 film with different underwater healing time at rt, sample width of 10 mm, a thickness of 0.5 mm, and a length of 30 mm at a loading rate of 20 mm min⁻¹ (the inset displays optical microscope image (6 × 4 mm) (left) before underwater and after underwater healing within 1 h at rt). g) Self‐healing efficiency of PDMS‐MDI_0.4‐TFB_0.6 film in different harsh condition. h) Self‐healing time and toughness performances comparison of our work with previously self‐healing elastomers at room temperature. Water‐assisted PDMS‐MDI_0.4‐TFB_0.6 simultaneously exhibited the highest toughness alongside rapid self‐healing time.

Figure 4

Schematic diagrams of WASHP‐based LETDs. a) Schematic illustration of LETDs structure. b) Durability test of the devices under 12 V (before and after pressure was applied onto the surface of the WASHP‐AgNW electrodes). c) Luminance–stretching cycle characteristics of the devices after repetitive stretching cycles at strains of 30%. d) Luminance characteristic of WASHP‐based LETDs during three consecutive autonomous self‐healing cycles (the inset of photograph of WASHP‐based LETDs operated at 12 V). e) Bendable and wrench LETDs (under 12 V). f) On–off light switch photograph of LETDs attached on the finger (under 12 V).

Figure 5

Schematic diagrams of WASHP‐based PeQDs WLED and backlight. a) Optical images of PeQDs solution (CsPbX₃ (X = Cl, Br, I)) and WASHP‐based PeQDs film under a 365 nm UV lamp, followed by self‐healing and mechanical test including bending and twisting. b) PL spectra of WASHP‐based PeQDs film immersed underwater with different healing time. c) Variation of Pb leakage concentrations over time of our WASHP‐based PeQDs film in the contaminated water measured by ICP‐MS spectra. d) Luminance emission of bilayer WASHP‐based PeQDs WLED (the inset picture displays the configuration of the prototype WLED device). e) EL spectrum of the WASHP‐based PeQDs WLED (3 V, 6 mA), represented in the inset picture. f) CIE color coordinates demonstrated pure white color rendering of our devices.