Shasha Yan,Lanfang Chai,Wei Li,Ling-Ping Xiao,Xiaohong Chen,Run-Cang Sun
Although pH-sensitive lignin-based materials have extensively attracted attentions because of the smart response to pH, it is still a challenge to realize the regulation of the pH-responsive properties. Focusing on this problem, we proposed a new method by tunning the content of hydroxyl groups to adjust the performances of lignin-based hydrogel (L-HG). The modified lignins with the hydroxyl content ranged from 0.31 to 5.91 mmol/g were obtained after acetylation or demethylation . As the results, when increasing the hydroxyl content, the gels became more compact and smooth, and the tensile strength reached 4.10 MPa. The strain was up to 83.2%, and the bending behavior occurred more easily at various pH (3, 5, 9, 11 and 13). While decreasing the hydroxyl content resulted in the impairments of almost all of the above performances. Based on the test of the moisture content, the pH-sensitive bending behavior might be mainly caused by the opposing forces of hydrophilic and hydrophobic interaction. Finally, the application test showed that the trimmed hydrogel could hook up 10 times weight greater than itself under both acid and alkaline conditions. We believe that this work would provide the theoretical guidance for the regulation of pH sensitivity of L-HG.
Tingting Xu,Sufang Guo,Miaomiao Li,Zhen Zhang,Baobao Pang,Yingmo Hu
Here, we report a composite film that shows multibending behaviors upon ultraviolet/visible (UV/vis) and near-infrared (NIR) light irradiations. First, an azobenzene-modified graphene oxide (AZO-GO) hybrid was prepared by the covalently grafting of 4-(3-triethoxysilylpropyl-ureido)azobenzene (TSUA) onto the surface of GO. A reversible change in the hydrophilicity of AZO-GO was observed upon UV/vis irradiations, due to the effective trans–cis-photoisomerization of azobenzene groups. Then, the AZO-GO hybrid powder was dispersed in ethanol and homogeneously mixed with the poly(vinyl alcohol) (PVA) aqueous solution to give a uniform and thin composite film (AZO-GO/PVA) with good flexibility by casting. Upon UV irradiation, this film bends rapidly toward the light source with a large amplitude and recovers to the original shape upon subsequent visible irradiation, due to the reversible trans–cis-photoisomerization of azobenzene groups. Upon NIR irradiation, the film curls slightly away from the light source, which is considered to be caused by the photothermal effect of the GO component. This composite film is also low-cost and uses facile manufacturing, with enhanced mechanical properties. Finally, by combining three pieces of the composite films, mimicking the reversible grabbing–release motions of a claw upon UV/vis irradiation was achieved.
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