Abstract
Tough gel with extreme temperature tolerance is a class of soft materials having potential applications in the specific fields that require excellent integrated properties under subzero temperature. Herein, physically crosslinked Europium (Eu)-alginate/polyvinyl alcohol (PVA) organohydrogels that do not freeze at far below 0°C, while retention of high stress and stretchability is demonstrated. These organohydrogels are synthesized through displacement of water swollen in polymer networks of hydrogel to cryoprotectants (e.g., ethylene glycol, glycerol, and d-sorbitol). The organohydrogels swollen water-cryoprotectant binary systems can be recovered to their original shapes when be bent, folded and even twisted after being cooled down to a temperature as low as −20 and −45°C, due to lower vapor pressure and ice-inhibition of cryoprotectants. The physical organohydrogels exhibit the maximum stress (5.62 ± 0.41 MPa) and strain (7.63 ± 0.02), which is about 10 and 2 times of their original hydrogel, due to the synergistic effect of multiple hydrogen bonds, coordination bonds and dense polymer networks. Based on these features, such physically crosslinked organohydrogels with extreme toughness and wide temperature tolerance is a promising soft material expanding the applications of gels in more specific and harsh conditions.
Highlights
Hydrogels are the typical soft materials, by virtue of their great potentials in applications spanning from soft robotics, sensors, actuators to tissue engineering (Wegst et al, 2014; Iwaso et al, 2016; Kim et al, 2016; Banerjee et al, 2018; Dong et al, 2018; Hu et al, 2019)
The procedure facilitates the formation of hydrogen bonds between the polymer chains in the Naalginate/polyvinyl alcohol (PVA) hydrogel
Na-alginate/PVA hydrogel was immersed in EuCl3 solution, and Eu3+ ions are accessible to anionic carboxyl groups in alginate structure center to form coordinate bonds (Figure 1D)
Summary
Hydrogels are the typical soft materials, by virtue of their great potentials in applications spanning from soft robotics, sensors, actuators to tissue engineering (Wegst et al, 2014; Iwaso et al, 2016; Kim et al, 2016; Banerjee et al, 2018; Dong et al, 2018; Hu et al, 2019). Improving mechanical properties of hydrogels became an important research hotspot. Almost all of the hydrogels swollen a large amount of water in polymer networks cannot resist a cold or hot environment (Wei et al, 2014, 2015; Wang W. et al, 2018), hindering the application of tough hydrogels in harsh conditions. Freezing and drying cause the hydrogels to hard, opaque and dry, which undoubtedly change the integrated mechanical properties of hydrogels, leading to unstable nature under wide temperature range (Han et al, 2017; Lou et al, 2019). It is still a challenge to design a hydrogel with enhanced and tunable mechanical strength together with extreme temperature tolerance
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