Versatile Liquid Metal/Alginate Composite Fibers with Enhanced Flame Retardancy and Triboelectric Performance for Smart Wearable Textiles

Abstract Liquid metal (LM) shows the superiority in smart wearable devices due to its biocompatibility and electromagnetic interference (EMI) shielding. However, LM based fibers that can achieve multifunctional integrated applications with biodegradability remain a daunting challenge. Herein, versatile LM based fibers are fabricated first by sonication in alginate solution to obtain LM micro/nano droplets and then wet‐spinning into LM/alginate composite fibers. By mixing with high‐concentration alginate solution (4–6 wt.%), the LM micro/nano droplets stability (colloidal stability for > 30 d and chemical stability for > 45 d) are not only improved, but also facilitate its spinning into fibers through bimetallic ions (e.g., Ga3+ and Ca2+) chelation strategy. These resultant fibers can be woven into smart textiles with excellent flexibility, air permeability, water/salt resistance, and high temperature tolerance (−196–150 °C). In addition, inhibition of smoldering result from the LM droplets and bimetallic ions is achieved to enhance flame retardancy. Furthermore, these fibers combine the exceptional properties of LM droplets (e.g., photo‐thermal effect and EMI shielding) and alginate fibers (e.g., biocompatibility and biodegradability), applicable in wearable heating devices, wireless communication, and triboelectric nanogenerator, making it a promising candidate for flexible smart textiles.


Supporting videos
Video S1 -Video S2

Stability analysis of LM droplets
The sedimentation force  1 of LM droplets in colloidal solution can be estimated analytically by the following equation: where  0 is the density of SA solution,  is the average diameter of LM droplets,  is the density of LM droplets, and  is the acceleration of gravity.According to Stokes law, the resistance  2 of the droplets during sedimentation can be expressed as follows: Where  is the kinetic viscosity of the suspension,  0 is the sedimentation velocity of the LM droplet.When the LM droplets are stable in the initial state, which is  1 =  2 , the sedimentation rate can be estimated analytically by the following equation: If assuming  = 150 nm,  = 6.3 g mL -1 ,  = 9.8 N Kg -1 .
Therefore, after mixing with high concentration alginate solution, the sedmimention velocity of LM droplets is much lower than the diluted alginate solution, which improve the colloidal stability significantly.It can be seen that the surface of these fibers has not been destroyed.(G) Mechanical test of LM/alginate fibers with three knots.

Figure S1 .
Figure S1.The effect of ultrasonication on alginate solution.(A) Schematic illustration of ultrasonication effect in the solution.(B-C) Comparison of viscosity (B) and visual image (C) of sodium alginate solution (4.6 wt%) before and after ultrasound.(D) Schematic illustration of the ultrasonic cavitation effect result in the broken of molecular entanglement of alginate chains.

Figure S3 .
Figure S3.Comparison of the stability of LM in sonication in different solutions.(A & B) SEM image of LM droplets sonicated in pure water (A) and 4.6 wt% alginate solution (B) and stored in different periods.(C) SEM images of LM droplets sonication in 0.5 wt% alginate solution and then mixing with 6.0 wt% alginate solution in different period.The insets are the corresponding photographs of LM dispersions.LM concentration: 20 mg mL -1 .

Figure S5 .
Figure S5.(A) SEM image of LM/alginate composite fibers of different diameters.(B) Diameter distribution of LM/alginate composite fibers.(C) Optical images of LM/alginate fibers in large scale preparation.

Figure S6 .
Figure S6.Typical SEM image and element mapping (Ga, Ca and O) of LM/alginate composite fibers.LM content: 40 wt%.

Figure S8 .
Figure S8.(A & B) The optical and SEM images of LM/alginate composite fibers immersed into the liquid nitrogen at -196 °C (A) and placed on the oven at 150 °C (B).

Figure S9 .
Figure S9.(A) The optical images of LM/alginate fibers and alginate fibers immersed in physiological saline solution (0.9 wt% NaCl) for 2 h.(B & C) The optical and SEM images of LM/alginate fibers immersed in pure water for 10 h (B) and 1 mol L -1 NaCl solution (C).

Figure S10 .
Figure S10.Gas permeability test of LM/alginate based textiles.The textiles were covered over bottles filled with hydrochloric acid, which showing the superior gas permeability.

Figure S11 .
Figure S11.(A & B) The contact angle measurement of alginate fiber fabric (A) and LM/alginate composite fiber fabric (B).

Figure S12 .
Figure S12.(A) Optical image of LM/alginate fibers (10 mg) soaked in methylene blue solution (100 mg L -1 ).(B) Comparison of adsorption amount and adsorption efficiency of alginate fibers and LM/alginate composite fibers for methylene blue.

Figure S15 .
Figure S15.(A & B) EMI SE T (A), SE R and SE A (B) of alginate fibers in the frequency ranges 8.2−12.4GHz.(C & D) SE R and SE A (C), R and A (D) of LM/alginate fibers in the frequency ranges 8.2−12.4GHz.LM content: 50 wt%.

Figure S16 .
Figure S16.(A) Schematic diagram of charge trapping for LM particles.(B) Schematic diagram of electrons hopping for LM/alginate composite fibers.

Figure S17 .
Figure S17.(A-C) Optical and SEM images before and after hundreds of cycles of LM/alginate fibers for washing test (A), bending test (B) and rubbing test (C).(D-F) LOI values (D), photo-thermal performance (E) and TENG performance (F) before and after hundreds of cycles of LM/alginate fibers for washing, rubbing and bending.