By virtue of a high conductivity comparable to rigid metals while possessing special deformability like liquid, liquid metal (LM) has presented a huge potential application in the field of flexible printed electronics. However, the typical core–shell structure for the LM ink, which aims to facilitate the stable dispersion of liquid metal nanoparticles (LMNPs), would impede their spontaneous connectivity and require extra techniques to externally rupture the organic shell layer, thus limiting the standardization for the LM ink application. Herein, we instead report an LM-based self-sintering conductive ink relying on inorganic montmorillonite (MMT) acting as an intercalated nanocomposite. In detail, we found that in the ethanol/water mixtures, hydrochloric acid (HCl) in combination with ultrasonication could induce the dissolution of the oxide shell of LMNPs and meanwhile achieve the exfoliation of MMT, subsequently self-assembling into a nanointercalated composite of LM-MMT due to the strong electrostatic interaction. When subjected to elevated temperature during curing, the MMT nanosheet would undergo a horizontally orientated stack and squeeze the LMNPs with the evaporation of the solvent, thus inducing their deformation, aggregation, and further connectivity, and finally, a conductive coating with a multilayered sandwich structure is formed. The optimized coating possessed an initially high electrical conductivity of up to 1.2 × 105 S m–1 and exhibited a unique anisotropic mechanical-electrical response, i.e., good resistance to shear deformation and sensitive response to tensile deformation. Moreover, the ink has good flowability and processability, allowing its availability on various flexible substrates with high-temperature resistance and long-term stability. Finally, LED array circuits, photosensitive circuits, and motion strain sensors were respectively fabricated on different flexible substrates as a proof of concept for the ink’s processability, electrical integration capability, and future application potential.
There is a growing demand for silver pastes and inks used in the field of printed electronics. The synthesis of organic surfactant stabilized silver micro-flakes by the solution-phase chemical reduction method at room temperature has attracted wide attention due to its simple equipment, convenient operation and affordable price. However, the electrical conductivity of silver micro-flakes-filled conductive pastes and inks are significantly influenced by residual surfactants. Therefore, the surface modification of silver micro-flakes to remove surface adsorbents becomes a key issue. In this study, the silver frameworks based on the self-sintering silver micro-flakes at room temperature are developed for silver pastes with excellent conductivity. The silver paste with 48 wt% of the sodium nitrate and succinic acid treated silver powders has a resistivity of 1.08 × 10 −6 Ω m and excellent adhesion strength after being cured at 140 °C in an oven.
Biodegradable conductive composites are key materials or components for printable transient electronics that can be fabricated in a low-cost and high-efficiency manner, thereby boosting their wide applications in biomedical engineering, hardware security, and environmental-friendly electronics. Continuous efforts in this area still lie in the development of strategies for highly conductive, safe, and reliable biodegradable conductive composite materials and devices. This paper introduces molybdenum/wax composites for multimodally printable transient electronics in which multiple transience modes including dissolution-induced degradation and thermally triggered degradation are available. Systematic experiments demonstrate several advantages and unique properties of this material system, including solvent-free fabrication, self-sintering behavior, and long-term and high conductivity via accelerable self-sintering treatment and rehealing capabilities. Notably, the immersion of molybdenum/wax composites in phosphate buffer solution can provide both positive effects (accelerated self-sintering-dominated) and negative effects (degradation-dominated) on their electrical conductivities. Mechanism analyses reveal the basis for balancing the degradation and accelerated self-sintering processes. The presented demonstrations foreshadow opportunities of the developed molybdenum/wax composites in rehealable electronics, on-demand smart transient electronics with multiple transience modes, and many other related unusual applications.
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