Kinetics of swelling and shrinking of poly (N-isopropylacrylamide) hydrogels at different temperatures
Kinetics of swelling and shrinking of poly (N-isopropylacrylamide) hydrogels at different temperatures
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DOI：
10.1016/s0927-7765(00)00155-7
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发表时间：
2000-12-15
影响因子：
5.8
通讯作者：
Ohshima, H
中科院分区：
文献类型：
--
作者：
Makino, K;Hiyoshi, J;Ohshima, H
研究了不同温度下干燥聚（N-异丙基丙烯酰胺）水凝胶在蒸馏水中的溶胀动力学。在高于33 ° C（LCST）的温度下30分钟后，凝胶中的水含量几乎没有增加，而在最初的30分钟内，水含量随时间增加。在25 - 33 ℃之间，含水量继续增加8小时，在较低温度下保持较高的增加比率。另一方面，在4 ℃的蒸馏水中溶胀的水凝胶在移动到保持在25 ℃和40 ℃之间的不同温度的蒸馏水中之后开始收缩。观察到两种类型的收缩行为高于和低于LCST。在水凝胶收缩过程的最初30 min内，温度越高，水含量下降越明显。然而，超过3小时后，在40 ℃下，水凝胶中保持的水含量几乎没有降低，并且在35 ℃下单位时间内的降低率最高。在37 ℃下，单位时间内水量的减少比例在1 h后随时间逐渐减小。因此，在溶胀的水凝胶的收缩过程持续24小时之后，水凝胶中保持的水含量在35 ℃下最低，而在干燥的水凝胶的溶胀过程持续24小时之后，水凝胶中保持的水含量在37和40 ℃下最低。根据这些发现，认为在水凝胶中存在至少三种类型的水分子。如下所示：（ii）在LCST周围形成的表皮相中的较松散的聚合物网络中可移动的水分子和吸附在聚合物链上的那些水分子;（iii）水分子通过氢键相互连接，吸附在亲水性聚合物链上，并在聚合物基质中可移动。(C)2000 Elsevier Science B. V.保留所有权利。
The swelling ratio of dried poly(N-isopropylacrylamide) hydrogels in distilled water was kinetically studied at different temperatures. The water content in the gel little increases after 30 min at higher temperatures than 33 degrees C (LCST), while it increases for the initial 30 min with time. Between 25 and 33 degrees C, the water content continues to increase for 8 hours, keeping the higher increase ratio at lower temperature. On the other hand, the hydrogel swollen in distilled water at 4 degrees C starts to shrink after the hydrogel being moved into the distilled water kept at different temperatures between 25 and 40 degrees C. There observed two types of shrinking behavior above and below LCST. In the initial 30 min of the shrinking process of the hydrogel, the water content decreases more obviously at higher temperatures. Over 3 h later, however, the water content kept in the hydrogel little decreases at 40 degrees C, and the decreasing ratio during a unit time is highest at 35 degrees C. At 37 degrees C, the decreasing ratio of the water amount during a unit time gradually decreases with time after 1 h. Therefore, the water content kept in the hydrogel after the shrinking process of the swollen hydrogel for 24 h is lowest at 35 degrees C, while that after the swelling process of dried hydrogel for 24 h is lowest at 37 and 40 degrees C. From these findings, it is considered that there are at least three types of water molecules in the hydrogels. as follows: (i) water molecules adsorbed on the hydrophobic polymer chains in the tight skin phase formed by the shrinkage of the hydrogel at 37 and 40 degrees C; (ii) water molecules movable in the looser polymer network in the skin phase formed around LCST and those adsorbed on the polymer chains; (iii) water molecules connected to each other with hydrogen bonds, adsorbed on the hydrophilic polymer chains, and movable in the polymer matrices. (C) 2000 Elsevier Science B.V. All rights reserved.