The Internal Network Dynamics of Poly(NIPAM) Based Copolymer Micro- and Macrogels: A Comparative Neutron Spin-Echo Study
The Internal Network Dynamics of Poly(NIPAM) Based Copolymer Micro- and Macrogels: A Comparative Neutron Spin-Echo Study
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聚（NIPAM）基共聚物微凝胶和大凝胶的内部网络动力学：中子自旋回波比较研究
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
T. Hellweg
中科院分区：
文献类型：
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作者：
Y. Hertle;M. Zeiser;P. Fouquet;M. Maccarini;T. Hellweg
微凝胶的合成通常高于所用聚合物(聚（n -异丙基-丙烯酰胺）（本例中为PNIPAM）的较低临界溶液温度（LCST），有证据表明，由于“不良”的溶剂条件以及单体和交联剂之间的反应性差异，交联剂在网络中的分布不均匀。相反，大凝胶在统计上是交联的，因为它们在LCST（良好的溶剂条件）下聚合。利用中子自旋回波（NSE）技术，可以研究聚合物网络在局部长度尺度上的扩散。由于交联剂在微凝胶和大凝胶中的分布本质上不同，因此可以预期网络的集体扩散会有所不同。然而，所研究的微凝胶和大凝胶的测量中间散射函数是相似的，并且都可以用单个指数衰减来描述，而不需要依赖于q的基线。因此，这两个系统在NSE实验中可用的长度尺度上表现为伪遍历式。测定凝胶网络呼吸模式DG的扩散系数和动态相关长度ξ可以得到同源微凝胶和大凝胶的可比值。所研究的微凝胶以丁烯酸为单体，并研究了pH对网络动力学的依赖性。
Abstract Microgels are generally synthesised above the lower critical solution temperature (LCST) of the used polymer (poly(N-isopropyl-acrylamide)(PNIPAM) in the present case) and there is evidence that, due to the “bad” solvent conditions and due to the differences in reactivity between the monomers and the crosslinker, an inhomogeneous crosslinker distribution in the network is created. In contrast, macrogels are statistically crosslinked, because they are polymerised below the LCST (good solvent conditions). With the neutron spin-echo (NSE) technique, the diffusion of the polymer network on a local length scale can be studied. Due to essentially different crosslinker distributions in the micro- and macrogels, a difference in the collective diffusion of the network could be expected. However, the measured intermediate scattering functions of the studied micro- and macrogel are similar and can both be described by a single exponential decay without a q-dependent baseline. Hence, both systems behave pseudo-ergodically on the length scale available in the NSE experiment. A determination of the diffusion coefficient of the breathing mode DG of the gel network and the dynamic correlation length ξ leads to comparable values for the homologous micro- and macrogels. The studied microgels contain butenoic acid as comonomer and also the pH dependence of the network dynamics is investigated.