Hydrogel-based strain sensors have been widely investigated owing to their intrinsic flexible and extensible properties. However, integrating good mechanical properties and excellent strain sensitivity into one hydrogel remains a challenge. In this work, a dual physical cross-linked carboxymethyl cellulose-Fe³⁺/polyacrylamide (CMC-Fe³⁺/PAAm) double network hydrogel was developed by facile two-step method. In this hydrogel, the Fe³⁺ cross-linked CMC acts as the first network for dissipating energy and hydrophobic association PAAm acts as the second network to maintain the integrity of hydrogel. Owing to these physical interactions, the as-prepared hydrogel shows good mechanical properties (e.g., tensile strength, 1.82 MPa; toughness, 6.52 MJ/m³). Furthermore, these mechanical behaviors can be modulated by adjusting the solid content, CMC/PAAm ratio, Fe³⁺ concentration and soaking time in Fe³⁺ solution. Moreover, the obtained hydrogel shows excellent self-recovery and anti-fatigue property due to the reversibility of dual physical cross-linked interactions. Additionally, the CMC-Fe³⁺/PAAm hydrogel shows good conductivity (1.82 S/m), strain sensitivity (gauge factor = 4.02 at 50–600% strain), and fast response time (260 ms). Based on the high strain sensitivity, the CMC-Fe³⁺/PAAm hydrogel can fabricate a flexible strain sensor for precisely monitoring various human motions. This study suggests that the CMC-Fe³⁺/PAAm hydrogel exhibits potential application in the flexible and stretchable strain sensors.

Graphic abstract

中文翻译：

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具有高拉伸性和韧性的双重物理交联羧甲基纤维素基水凝胶，作为敏感的应变传感器

基于水凝胶的应变传感器因其固有的柔韧性和可扩展性而被广泛研究。然而，将良好的机械性能和优异的应变敏感性整合到一种水凝胶中仍然是一个挑战。在这项工作中，通过简便的两步法开发了一种双物理交联的羧甲基纤维素-Fe ³⁺ /聚丙烯酰胺（CMC-Fe ³⁺ / PAAm）双网络水凝胶。在该水凝胶中，Fe ³⁺交联的CMC充当用于耗散能量的第一网络，而疏水缔合PAAm充当第二网络以维持水凝胶的完整性。由于这些物理相互作用，所制备的水凝胶显示出良好的机械性能（例如，拉伸强度为1.82 MPa；韧性为6.52 MJ / m ^3）。）。此外，可以通过调节固含量，CMC / PAAm比，Fe ³⁺浓度和在Fe ³⁺溶液中的浸泡时间来调节这些机械行为。此外，由于双重物理交联相互作用的可逆性，所获得的水凝胶显示出优异的自我恢复和抗疲劳性能。另外，CMC-Fe ³⁺ / PAAm水凝胶显示出良好的电导率（1.82 S / m），应变敏感性（应变系数= 50-600％时为4.02）和快速响应时间（260 ms）。基于高应变敏感性，CMC-Fe ³⁺ / PAAm水凝胶可制造出柔性应变传感器，以精确监控各种人体运动。这项研究表明，CMC-Fe ³⁺/ PAAm水凝胶在柔性和可拉伸应变传感器中具有潜在的应用前景。

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