Anti-Freezing, Non-Drying, Localized Stiffening, and Shape-Morphing Organohydrogels

Abstract

Artificial shape-morphing hydrogels are emerging toward various applications, spanning from electronic skins to healthcare. However, the low freezing and drying tolerance of hydrogels hinder their practical applications in challenging environments, such as subzero temperatures and arid conditions. Herein, we report on a shape-morphing system of tough organohydrogels enabled by the spatially encoded rigid structures and its applications in conformal packaging of “island–bridge” stretchable electronics. To validate this method, programmable shape morphing of Fe (III) ion-stiffened Ca-alginate/polyacrylamide (PAAm) tough organohydrogels down to −50 °C, with long-term preservation of their 3D shapes at arid or even vacuum conditions, was successfully demonstrated, respectively. To further illustrate the potency of this approach, the as-made organohydrogels were employed as a material for the conformal packaging of non-stretchable rigid electronic components and highly stretchable liquid metal (galinstan) conductors, forming a so-called “island–bridge” stretchable circuit. The conformal packaging well addresses the mechanical mismatch between components with different elastic moduli. As such, the as-made stretchable shape-morphing device exhibits a remarkably high mechanical durability that can withstand strains as high as 1000% and possesses long-term stability required for applications under challenging conditions.

Photodegradable Non‐Drying Hydrogel Substrates for Liquid Metal Based Sustainable Soft‐Matter Electronics

“…[ 39 ] In addition, one of the major challenges in using hydrogels as substrates is water evaporation, which alters the mechanical and surface properties of the hydrogel over time. [ 40 ] Therefore, our initial attempts to print the circuit over the hydrogel substrate failed due to these problems.…”

“…The immersion time plays an important role in the long-term stability of the hydrogels because by improving weight retention, which depends on the wt.% of glycerol incorporated. [40,41] To verify the liquid retention ability, the hydrogels were evaluated by weight measurements during 30 days of storage at 22 °C and 60% humidity (Figure 2A-C). As expected, the water-based hydrogels exhibited low water retention (20.8 wt.% after 1 day), which resulted in compromised mechanical properties (tensile strain, modulus, and flexibility) and caused a mechanical deformation (Figure 2B, Figure S1, Supporting Information).…”

Highly Sensitive Temperature Detection Based on a Frost- and Dehydration-Resistive Ion-Doped Hydrogel-MXene Composite

“…However, most hydrogels tend to dehydrate gradually under ambient conditions and freeze at subzero temperatures. − To overcome these problems, strategies such as solvent replacement , and salt treatment method have been developed . Although using organic solvents such as polyols (e.g., glycerol and glycol) as partial substitutes for water in hydrogels can improve their resistance to freezing and dehydration, polyols often exhibit insulating properties, which can restrict the electronic applications of hydrogels . In contrast, salts such as LiBr, MgCl 2 , and CaCl 2 can not only confer hydrogels with antifreezing and dehydration properties but also improve their ionic conductivities. , However, the application of salt-treated hydrogels in temperature sensing has received limited exploration …”