Strong, tough, ionic conductive, and freezing-tolerant all-natural hydrogel enabled by cellulose-bentonite coordination interactions

Abstract

Ionic conductive hydrogels prepared from naturally abundant cellulose are ideal candidates for constructing flexible electronics from the perspective of commercialization and environmental sustainability. However, cellulosic hydrogels featuring both high mechanical strength and ionic conductivity remain extremely challenging to achieve because the ionic charge carriers tend to destroy the hydrogen-bonding network among cellulose. Here we propose a supramolecular engineering strategy to boost the mechanical performance and ionic conductivity of cellulosic hydrogels by incorporating bentonite (BT) via the strong cellulose-BT coordination interaction and the ion regulation capability of the nanoconfined cellulose-BT intercalated nanostructure. A strong (compressive strength up to 3.2 MPa), tough (fracture energy up to 0.45 MJ m−3), yet highly ionic conductive and freezing tolerant (high ionic conductivities of 89.9 and 25.8 mS cm−1 at 25 and −20 °C, respectively) all-natural cellulose-BT hydrogel is successfully realized. These findings open up new perspectives for the design of cellulosic hydrogels and beyond.

Rapid Preparation of Antifreezing Conductive Hydrogels for Flexible Strain Sensors and Supercapacitors

“…The high moisture content of the hydrogels will form ice crystals at subzero temperatures, which makes it difficult for polymer chains to move, causing hydrogel electronics to lose their excellent performance, including conductivity, transparency, and flexibility. , Therefore, the development of freezing-resistant hydrogels is greatly significant for the stable operation of hydrogel-based electronics at subzero temperatures. Efforts have been devoted to improving the freezing resistance of the conductive hydrogel via the introduction of inorganic salts, such as NaCl, CaCl 2 , LiCl, and so forth. , Inorganic salts could significantly lower the freezing point by weakening the internal hydrogen bonding between water molecules . Suo et al developed a double network hydrogel by soaking the polyacrylamide sodium alginate hydrogel in the high-concentration solution of CaCl 2 .…”

Rarely negative-thermovoltage cellulose ionogel with simultaneously boosted mechanical strength and ionic conductivity via ion-molecular engineering

“…27 In such ion-conductive gels, a significant amount of electrolyte is added to improve the system conductivity; however, electrolyte overload then compromises the mechanical properties of the gels. 27–30 For instance, Ouyang's group developed an iTE gel composed of an organic polymer (waterborne polyurethane, WPU) and electrolyte (1-ethyl-3-methylimidazolium dicyanamide, EMIM:DCA), where increasing EMIM:DCA loading increased the ionic conductivity of the gel from 0.08 (10 wt% loading) to 11.7 mS cm −1 (50 wt% loading). However, the mechanical strength of the as-prepared iTE gel decreased from 4.2 to 0.6 MPa when EMIM:DCA amount increased from 20 wt% to 40 wt%.…”

Manta Ray Inspired Soft Robot Fish with Tough Hydrogels as Structural Elements

“…However, most hydrogels, including tough ones, have an elastic modulus on the kPa level, − which cannot provide sufficient structural stiffness and generate thrust force for continuous motions of hydrogel-based underwater soft robots. In recent years, various tough and stiff hydrogels with a wide spectrum of mechanical performances have been developed and recognized as a new kind of engineering material to construct versatile soft machines. − However, there is no report on the design of underwater soft robots with tough hydrogels as the structural elements.…”