Inhomogeneity in Hydrogels Synthesized by Thiol-Ene Polymerization
Inhomogeneity in Hydrogels Synthesized by Thiol-Ene Polymerization
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DOI：
10.1021/ma302520p
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发表时间：
2013-03-12
期刊：
影响因子：
5.5
通讯作者：
Oppermann, Wilhelm
中科院分区：
文献类型：
--
作者：
Grube, Svenja;Oppermann, Wilhelm
通过硫醇-烯聚合合成的水凝胶的特征在于相对于其宏观性能通过弹性测量和其微观性能，特别是不均匀性，通过动态光散射。为了比较，相同的研究，聚丙烯酰胺（PAAm）水凝胶制备自由基链增长交联共聚。机械测量证明，对于这两种类型的凝胶的网络缺陷的程度是广泛变化的不同浓度，而在特定浓度下观察到的宏观性能是非常相似的。然而，作为凝胶不均匀性的量度的静态散射的分数显著地取决于当在制备状态下进行测量时所研究的网络的类型。大多数的硫醇-烯凝胶出现均匀的，相反的PAAm凝胶。在平衡溶胀状态下，情况完全不同，其中所有凝胶都表现出极高且几乎相同的静态散射强度分数，而与其合成中所采用的反应类型或浓度无关。这些观察结果意味着：（i）网络缺陷和均匀性之间没有明确的相关性，（ii）交联反应的类型控制着制备状态下的浓度不均匀性，但不控制（iii）网络密度的不均匀性。当凝胶溶胀时可见后者。
Hydrogels synthesized via thiol-ene polymerization were characterized with respect to their macroscopic properties via elasticity measurements and to their microscopic properties, in particular inhomogeneity, by dynamic light scattering. For comparison, identical studies were made on polyacrylamide (PAAm) hydrogels prepared by free-radical chain-growth cross-linking copolymerization. Mechanical measurements prove that for both types of gels the degree of network imperfections is widely varied by varying concentration, while the macroscopic properties observed at particular concentrations are very similar. However, the fraction of static scattering which is a measure of gel inhomogeneity depends significantly on the type of network studied when the measurement is performed in the state of preparation. The majority of the thiol-ene gels appear homogeneous, contrary to the PAAm gels. The situation is completely different in the equilibrium swollen state, where all gels exhibit extremely high and almost identical fractions of static scattering intensity, irrespective of the type of reaction or the concentration employed in their synthesis. These observations imply that (i) there is no clear correlation between network imperfections and homogeneity and (ii) the type of cross linking reaction controls the concentration inhomogeneity in the state of preparation but not (iii) the inhomogeneity of network density. The latter is seen when the gels are swollen.