Ultrastretchable and Antifreezing Double-Cross-Linked Cellulose Ionic Hydrogels with High Strain Sensitivity under a Broad Range of Temperature

Abstract

Stretchable and antifreezing conductive hydrogels, especially prepared from natural polymers, are beneficial for important and rapidly growing stretchable electronic devices. Unfortunately, the potential value of the pure natural polymer-based hydrogel in such applications is very limited because of its poor mechanical behavior and inevitable freeze of water-based hydrogels at subzero temperatures. Herein, we report the ultrastretchable and antifreezing double-cross-linked cellulose ionic hydrogels (DCIHs) prepared by ammonium persulfate initiating free radical polymerization of allyl cellulose and by NaCl inducing physical cross-linking. The acquired hydrogels display ultrastretchability (∼236% of tensile strain) and high compressibility (∼82% of compression strain) among pure polysaccharide-based hydrogels including cellulose, chitosan, and chitin. Simultaneously the soaking strategy in saturated NaCl solution also endows the DCIHs with excellent antifreezing properties that not only have good stretchability (strain up to ∼100%) at −24 °C but also surprisingly transform into high visual transparency under a wide range of low temperature (−30 to −16 °C). In addition, the DCIH with high reliability, response speed, as well as wide range strain sensor is also demonstrated by investigating the output electrical signals, showing the potential for applications in flexible electronics under a broad range of temperature.

MXene‐Based Conductive Organohydrogels with Long‐Term Environmental Stability and Multifunctionality

“…The hydrogel without Gly displays a sharp peak at ≈0 °C, which is attributed to the thawing of the ice in the sample. [ 29 ] With the increase in Gly, the organohydrogel demonstrates a significantly improved freezing resistance (Figure 3a–b and Figure S6, Supporting Information). In particular, when the Gly content reached 20 wt% (PTCM‐Gly5), no crystallization peak was observed in the DSC curves, suggesting good mechanical stability of the PTCM‐Gly5 sample in the range of −80 to 50°C.…”

Highly Stretchable, Strain-Sensitive, and Ionic-Conductive Cellulose-Based Hydrogels for Wearable Sensors

“…The synthesis of allyl cellulose was performed following a previously published method [22]. Briefly, to obtain a transparent 6 wt% cellulose solution, the cellulose was dissolved in 7 wt%…”

“…The synthesis of allyl cellulose was performed following a previously published method [22]. Briefly, to obtain a transparent 6 wt% cellulose solution, the cellulose was dissolved in 7 wt% NaOH/12 wt% urea solution at a temperature under −12.5 • C. Then, allyl glycidyl ether (of molar ratio 8.0 to anhydroglucose unit of cellulose) was added dropwise into the transparent cellulose solution, under a nitrogen atmosphere, at 30 • C for 24 h. Thereafter, the residual allyl glycidyl ether in the mixture was removed by thorough washing with ether, then the mixture was further rotary-evaporated for 1 h at 30 • C. Additionally, for the structural characteristics of allyl cellulose, the mixture was thoroughly washed with acetone, then the purified sample was obtained by further dialyzing for 3 days [22].…”

“…For example, Zhao et al constructed high-strength and high-toughness cellulose hydrogels by chemical cross-linking with epichlorohydrin Polymers 2019, 11, 2067 2 of 10 followed by physical cross-linking induced by an ethanol solution [15]. In our previous study, ultra-stretchable cellulose ionic hydrogels were prepared by using (NH 4 ) 2 S 2 O 8 to initiate free radical polymerization, then using NaCl to induce physical cross-linking [22]. However, although high mechanical performance was obtained, there remains the challenge of combining the properties of transparency, high sensitivity, and high mechanical performance to construct wearable sensors that imitate the human skin (with 2-80 KPa of modulus for the dermis and 140-600 KPa of modulus for the epidermis) [23][24][25].…”

Electrical and Capacitive Response of Hydrogel Solid-Like Electrolytes for Supercapacitors

“…Although currently, polyvinyl alcohol (PVA)-based gels are the most widely used electrolytes for solid-state supercapacitors, [ 1 , 18 ] biopolymer-derived systems are gaining increasing attention. For example, polysaccharides, [ 19 , 20 , 21 , 22 , 23 ] proteins and polypeptides, [ 24 , 25 , 26 , 27 ] and even synthetic polymers incorporating biological units, such as polyesteramides, [ 28 , 29 ] have been used to prepare hydrogels as solid-like electrolytes for manufacturing bioinspired supercapacitors. Indeed, their electrochemical response has been well studied by cyclic voltammetry and galvanostatic charge-discharge cycles; [ 1 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ] however, their ionic conductivity and capacitive properties remain unknown in many cases.…”