Stretchable and transparent alginate ionic gel film for multifunctional sensors and devices.

Flexible and stretchable substrates based on pure natural polymers have attracted widespread attention for next-generation "green" electronics. However, fabrication of stretchable and "green" electronic sensors with integrated high stretchability, optical transmittance and good conductivity still remains tremendous challenges. Herein, alginate ionic gel films (AIGFs) with integrated high stretchability (tensile strength of 4.13 MPa and 191.1 % fracture strain) and excellent transparent properties (transparency of ∼92 %) are achieved by the glycerol inducing physical crosslinking and CaCl2 initiating ionic crosslinking, a simple soaking and drying strategy. The obtained gel films not only exhibit good ionic conductivity, but also high reliability, wide-range sensing, and multiple sensitivity to external stimulus. More importantly, these ionic conductive gel films as green substrates are successfully utilized for construction of flexible and patterned optoelectronic devices. This promising strategy will open up new powerful routes to construct highly stretchable, transparent, and ionic conductive substrates for multifunctional sensors and devices.

Stretchable and sensitive sodium alginate ionic hydrogel fibers for flexible strain sensors.

Ionic conductive hydrogel fibers based on natural polymers provide an immense focus for a new generation of electronics due to their flexibility and knittability. The feasibility of utilizing pure natural polymer-based hydrogel fibers could be drastically improved if their mechanical and transparent performances satisfy the requirements of actual practice. Herein, we report a facile fabrication strategy for significantly stretchable and sensitive sodium alginate ionic hydrogel fibers (SAIFs), by glycerol initiating physical crosslinking and by CaCl2 inducing ionic crosslinking. The obtained ionic hydrogel fibers not only show significant stretchability (tensile strength of 1.55 MPa and fracture strain of ∼161 %), but also exhibit wide-range sensing, satisfactorily stable, rapidly responsive, and multiply sensitive abilities to external stimulus. In addition, the ionic hydrogel fibers have excellent transparency (over 90 % in a wide wavelength range), and good anti-evaporation and anti-freezing properties. Furthermore, the SAIFs have been easily knitted into a textile, and successfully applied as wearable sensors to recognize human motions, by observing the output electrical signals. Our methodology for fabrication intelligent SAIFs will shed light on artificial flexible electronics and other textile-based strain sensors.