In recent years, ionic conductive hydrogels have shown great potential for application in flexible sensors, energy storage devices, and actuators. However, developing facile and effective methods for fabricating such hydrogels remains a great challenge, especially for hydrogels that retain their properties in extreme environmental conditions, such as at subzero temperatures or storage in open-air conditions. Herein, a water-miscible ionic liquid (IL), such as 1-ethyl-3-methylimidazolium acetate (EMI-mAc), was introduced to form an IL/water binary solvent system for poly(vinyl alcohol) (PVA) to create ionic conductive PVA hydrogels. The physically crosslinked PVA/EMImAc/H 2 O hydrogels showed better mechanical properties and transparency than the traditional PVA hydrogel prepared by the freeze−thaw method due to the formation of homogeneous and small PVA microcrystals in the EMImAc/H 2 O binary solvent system. More importantly, the PVA/EMImAc/H 2 O hydrogel exhibited significant anti-freezing and water-retaining properties because of the presence of the IL. The hydrogels remained flexible and conductive at temperatures as low as −50 °C and retained more than 90% of their weight after storage in open-air conditions for 2 weeks. In addition, the thermal stability of the hydrogel could be increased to 95 °C through the addition of Mg(II) ions. A multimodal sensor based on the PVA/EMImAc/H 2 O/Mg(II) hydrogel showed high sensitivity and a quick response to changes in pressure, strain, and temperature, with both long-term stability and a wide working temperature range. This study may open a new route for the fabrication of functional PVA-based hydrogel electrolytes and provide a practical pathway for their use in multifunctional electronic and sensory device applications.
Flexible
ionic conductive hydrogel is attracting significant interest
as it could be one of the crucial components for multifunctional ionotronic
devices. However, their features of inevitably drying out without
package and freezing at subzero temperatures may greatly limit the
applications of conventional hydrogels in specific situations. Here,
we present an ionic conductive hydrogel with water retention and freezing
tolerance that consists of silk fibroin, ionic liquid, water, and
inorganic salt. It is discovered that the ionic liquid serves multiple
purposes to prevent water evaporation, decrease the freezing point,
provide the essential conductivity of the hydrogel, etc. As a binary
mixed solvent, the ionic liquid/water mixture enhances both water
retention and freezing tolerance of the hydrogel electrolyte. Based
on the silk fibroin (SF)/1-ethyl-3-methylimidazolium acetate (EMImAc)/H2O/KCl hydrogel electrolyte, the flexible fiberlike supercapacitor
could still function well at a temperature as low as −50 °C
and after being stored in the open air for a long time. It is anticipated
that this hydrogel will prove useful in developing new applications
operating under harsh environments.
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