Large deformation behavior and effective network chain density of swollen poly(N-isopropylacrylamide)–Laponite nanocomposite hydrogels
Large deformation behavior and effective network chain density of swollen poly(N-isopropylacrylamide)–Laponite nanocomposite hydrogels
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DOI：
10.1039/c1sm06484c
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发表时间：
2012
期刊：
影响因子：
3.4
通讯作者：
Tao Wang;Danjie Liu;Cuixia Lian;Shudian Zheng;Xinxing Liu;Zhen Tong
中科院分区：
文献类型：
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作者：
Tao Wang;Danjie Liu;Cuixia Lian;Shudian Zheng;Xinxing Liu;Zhen Tong
水凝胶通常用于水和/或生理盐水介质中，因此，溶胀凝胶的力学性能尤为重要。到目前为止，这些数据是缺乏的，因为最膨胀的水凝胶太弱和太脆，根本无法进行变形测试。研究了膨胀型聚N-异丙基丙烯酰胺(PNIPAM)-膨润土纳米复合水凝胶(NC凝胶)在大应变变形条件下的压缩和拉伸力学行为。膨胀的NC凝胶在压缩后完好无损，并保持高达500%的伸长率。在溶胀的NC凝胶中首次观察到应变硬化，这被认为是由于磷灰石片层的取向而导致的聚合物网络链的伸长限制。因此，增加NC凝胶中的膨润土含量可以提高其应变硬化能力。当变形量较小时，用Mooney-Rivlin模型定量描述了制备和膨胀的NC凝胶的压缩和伸长应力-变形曲线。而对于大变形，考虑有限延伸性的Creton模型能够几乎定量地预测这些曲线。在制备和溶胀的NC凝胶中发现了应力-变形滞后现象，这是由于粘土片的去取向和高分子链的松弛所致。粘土片的取向过程在变形过程中耗散了能量，导致NC凝胶即使在膨胀状态下也具有较高的韧性。溶胀后的NC凝胶的有效网链密度表明，在水中的溶胀只会使凝胶体积增大，而不会破坏交联点。粘土层片层的有效网链数目几乎与粘土含量无关，因此粘土层片层的加入形成了新的交联连接。
Hydrogels were often used in aqueous and/or physiological saline media, thus, the mechanical properties of the swollen gels were of particular importance. Until now, these data were lacking due to the most swollen hydrogels being too weak and brittle to undergo the deformation test at all. The mechanical behavior of swollen poly(N-isopropylacrylamide) (PNIPAm)–Laponite nanocomposite hydrogels (NC gels) were studied with compression and elongation under large strains causing deformation. The swollen NC gels were intact after compression and sustained elongation of up to 500%. Strain hardening was observed in the swollen NC gels for the first time, which was considered to be the extensional limitation of the polymer network chains due to the orientation of the Laponite platelets. Therefore, the strain hardening was enhanced by increasing the Laponite content in the NC gels. When the deformation was low, the compression and elongation stress-deformation curves of the as-prepared and swollen NC gels were described quantitatively with the Mooney–Rivlin model. Whilst for high deformation, Creton's model considering the finite extensibility enabled the prediction of these curves almost quantitatively. Stress-deformation hysteresis was found in the as-prepared and swollen NC gels, which was the result of the deorientation of the clay platelets and relaxation of the polymer chains. The orientation process of the clay platelets dissipated energy during deformation, resulting in a high toughness of the NC gels even in the swollen state. The effective network chain density in the swollen NC gels manifested that the swelling in water only expanded the gel volume and did not damage the cross-linking points. The number of effective network chains attached to one Laponite XLS platelet was almost independent of the clay content, so the addition of clay platelets in the NC gel formed new cross-linking junctions.