Microfluidic Generation of Microsprings with Ionic Liquid Encapsulation for Flexible Electronics.

Inspired by helical or spiral veins, which endow plants with excellent flexibility and elasticity to withstand storms, we present novel hollow microsprings with ionic liquid encapsulation for flexible and stretchable electronics. The microsprings were generated by using a coaxial capillary microfluidic device to consecutively spin poly(vinylidene fluoride) (PVDF) presolution and an ionic liquid, which formed laminar flows in the coaxial injection microfluidic channels. The fast phase inversion of PVDF helps to form the core-shell structure of a microfiber and guarantees the in situ encapsulation of ionic liquid. The hybrid microfiber can then spiral and be further solidified to maintain the helical structure with increasing flow rates of the injection fluids. Because of the feasible and precise control of the injection fluids during the microfluidic spinning, the resultant microsprings have controlled core-shell structures, helical pitches, and corresponding electromechanical properties. By further embedding them into stretchable films, the simple paradigm of a flexible device shows great conductive performance in tensile tests and even motion cycles, which could be explored as a promising candidate in stretchable sensors, flexible electronics, and electronic skins.