Fluorescence study on the mechanism of rapid shrinking of grafted poly(N-isopropylacrylamide) gels and semi-IPN gels
Fluorescence study on the mechanism of rapid shrinking of grafted poly(N-isopropylacrylamide) gels and semi-IPN gels
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DOI：
10.1016/j.polymer.2005.01.100
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发表时间：
2005-08
期刊：
影响因子：
4.6
通讯作者：
Etsuko Yoshinari;H. Furukawa;K. Horie
中科院分区：
文献类型：
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作者：
Etsuko Yoshinari;H. Furukawa;K. Horie
为了在纳米尺度上阐明接枝聚（N-异丙基丙烯酰胺）（PNIPAM）水凝胶在从室温跃升至40°C过程中快速收缩的机制，研究了丹磺酰基团附着在接枝链或网络主链上的快速收缩接枝PNIPAM凝胶的丹磺酰荧光的温度依赖性。接枝 PNIPAM 凝胶中的接枝链在 540 至 500 nm 范围内，随着温度在 17°C 至 32°C 之间升高，丹磺酰荧光峰值波长 λf 逐渐减小，表明在此温度范围内接枝链发生了卷曲球转变。然而，λfof 网络主链在 30–34°C 下从 540 nm 急剧下降到 510 nm，再现了 PNIPAM 凝胶的宏观体积相变。卷曲球转变和接枝链的进一步聚集增强了温度跳跃过程中异质结构的形成，在塌陷的 PNIPAM 凝胶的表层提供了排水通道。提出了尺寸远大于网络网格尺寸的大规模异质性对快速收缩的可能重要性，因为这种类型的大规模异质性可以通过在线性大单体存在下形成网络来引入。后交联的半互穿网络凝胶也表现出内部线性聚合物链的快速收缩和 λf 逐渐减小。
In order to clarify in nanometer scale the mechanism of rapid shrinking of grafted poly(N-isopropylacrylamide) (PNIPAM) hydrogels during temperature jump from room temperature to 40°C, temperature dependences of dansyl fluorescence were studied for the rapid-shrinking grafted PNIPAM gels in which dansyl groups are attached to graft chains or network main chains. Gradual decrease in dansyl fluorescence peak wavelength, λf, with the increase in temperature between 17 and 32°C for grafted chains in the grafted PNIPAM gel from 540 to 500nm showed the occurrence of coil-globule transition of graft chains during this temperature range. However, λfof network main chains showed abrupt decrease at 30–34°C from 540 to 510nm reproducing the macroscopic volume phase transition of PNIPAM gels. The coil-globule transition and further aggregation of graft chains enhance the formation of heterogeneous structure during the temperature jump, providing water-expelling channels at the surface skin layer of the collapsed PNIPAM gel. The possible importance of large-scale heterogeneity with a much larger size than the mesh size of network on the rapid-shrinking is suggested, because this type of large-scale heterogeneity can be introduced by the network formation in the presence of linear macromonomer. A post-crosslinked semi-IPN gel also showed rapid shrinking and gradual decrease in λffor the linear polymer chains inside.