Recently, Suo Zhigang, the academician from Harvard University, and Yang Canhui from Southern University of Science and Technology have designed a multistep dip‐coating process to enable hydrogel ionotronics of diverse configurations. This process integrates hydrogels and hydrophobic elastomers with strong adhesion, not damaging the stretchability and transparency.
The research started from coaxial ionotronic luminescent fibers made up of hydrogel cores, luminescent layers, hydrogel layers and elastomer layers. The cations and anions regularly accumulate in the hydrogel/elastomer surfaces under the alternating voltage between the hydrogel core and the hydrogel layer, to create alternating electric field in the luminescent layer and the electrons among the phosphor particles for light production.
Researchers compared two steps: the hydrogel dip-coated with elastomer and the elastomer dip-coated with hydrogel. The researchers found that the elastomer precursor solution could spread on the hydrogel surface spontaneously while the water remained a droplet on the elastomer. After the priming process of Silane Coupling Agent, the water could spread on the surface of the elastomer.
The light produced by the fiber was on and off with two metal wires connected to power source. The ionotronic luminescent fiber can be stretchable and maintain its original luminance after stretching, which can be lengthened to 1.5 times its original length and keeps its peak stress and luminance after 10,000 cycles.
The softness and stretchability of hydrogel, the high cohesion between hydrogel and elastomer and the applicability of dip-coating process enable the complicatedly shaped hydrogel ionotronics to produce light.