Network chain density and relaxation of in situ synthesized polyacrylamide/hectorite clay nanocomposite hydrogels with ultrahigh tensibility
Network chain density and relaxation of in situ synthesized polyacrylamide/hectorite clay nanocomposite hydrogels with ultrahigh tensibility
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DOI：
10.1016/j.polymer.2008.09.021
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发表时间：
2008-10
期刊：
影响因子：
4.6
通讯作者：
Lijun Xiong;Xiaobo Hu;Xinxing Liu;Zhen Tong
中科院分区：
文献类型：
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作者：
Lijun Xiong;Xiaobo Hu;Xinxing Liu;Zhen Tong
纳米复合水凝胶（NC 凝胶）D-AM 和 S-AM 分别通过丙烯酰胺（AM）与锂皂石 RD 和 RDS 锂蒙脱石粘土的原位聚合合成。在不同的十字头速度下观察NC凝胶的拉伸性能，所有NC凝胶都表现出极高的拉伸性，例如，断裂伸长率甚至高于4000%，除了锂皂石含量最低为1 w/v%的两个样品之外。在伸长回复曲线中观察到强烈的拉伸滞后，表明 NC 凝胶缓慢松弛。线性粘弹性内的动态模量 G' 和 G'' 表明，这些凝胶中形成了具有锂皂石片状连接处的网络结构。 Laponite RD 表现出比焦磷酸四钠改性 Laponite RDS 更强的凝胶能力。 NC 凝胶的松弛模量 G(t) 与慢速橡胶松弛相似，临界指数 n 约为 0.16，远低于溶胶-凝胶转变时临界凝胶的 0.66-0.71。相比之下，化学交联的水凝胶在相同的时间间隔内几乎没有表现出松弛。 NC凝胶的有效网络链密度由平衡剪切模量确定，明显低于化学交联水凝胶。目前的结果表明，这些 NC 凝胶的高变形能力来自于其低有效网络链密度和适度的松弛。
Nanocomposite hydrogels (NC gel) D-AM and S-AM were synthesized through in situ polymerization of acrylamide (AM) with hectorite clays of Laponite RD and RDS, respectively. The tensile performance of the NC gel was observed at different crosshead speeds and all of the NC gels exhibited an extremely high tensibility, e.g., the elongation at break even higher than 4000%, except for two samples with the lowest Laponite content of 1 w/v%. Strong tensile hysteresis was observed in the elongation–reversion curve, indicating a slow relaxation in the NC gels. Dynamic moduli G′ and G″ within linear viscoelasticity illustrated that the network structure was formed in these gels with the junction of Laponite platelets. The Laponite RD showed stronger gelation capability than the tetrasodium pyrophosphate modified Laponite RDS. The relaxation modulus G(t) for the NC gels was found to be similar to the slow rubber relaxation with the critical exponent n of about 0.16, much lower than 0.66–0.71 for the critical gel at the sol–gel transition. In comparison, the chemically cross-linked hydrogel showed almost no relaxation during the same time interval. The effective network chain density of the NC gel was determined from equilibrium shear modulus, which was evidently lower than that of the chemically cross-linked hydrogels. The present results reveal that the high deformability of these NC gels comes from their low effective network chain density with moderate relaxation.