Nottingham Trent University, School of Science and Technology, Clifton Campus, Nottingham, NG 11 8NS, UK.
Soft Matter. 2014 Mar 28;10(12):2035-46. doi: 10.1039/c3sm52887a.
Free-radical polymerisation of acrylamide derivatives in the presence of exfoliated clay platelets has recently emerged as a new technique for the synthesis of strong and tough nanocomposite hydrogels (NCHs) with a unique hybrid organic/inorganic network structure. The central intent of many research studies in the field of NCHs conducted so far was to change hydrogel properties with the introduction of various clays and variation of the clay content. Here, we demonstrate that the properties of NCHs significantly vary depending on initiating conditions used for hydrogel synthesis via in situ polymerisation in solutions of high monomer concentrations (above 1 mol L(-1)). A unique, complementary combination of real-time dynamic rheology and pulsed NMR/MRI has been used to study the influence of the composition of a redox initiating system on the gelation process and hydrogel properties. The molar ratio of the persulphate initiator to tertiary amine activator affects the polymerisation kinetics, morphology and mechanical properties of the hydrogels. We further show that activator-dominated systems tend to produce hydrogels with higher storage modulus and lower water intake. This trend is attributed to the increase in the cross-linking degree. From the analysis of the water state in NCH and hydrogels prepared with and without an organic cross-linker, it was concluded that clay platelets did not form covalent bonds with polymer molecules but contributed to the formation of a physical network. There is evidence of self-crosslinking of polymer chains during acrylamide polymerisation at high monomer concentration. The composition of the initiating system influences the number of formed self-crosslinks.
在剥离的粘土片层存在下，丙烯酰胺衍生物的自由基聚合最近已成为合成具有独特的有机/无机混合网络结构的强韧纳米复合水凝胶（NCH）的新技术。迄今为止，在 NCH 领域进行的许多研究的主要目的是通过在高单体浓度（高于 1mol L(-1)）的溶液中进行原位聚合来改变水凝胶的性能，引入各种粘土并改变粘土的含量。在这里，我们证明了 NCH 的性能会根据在溶液中通过原位聚合形成水凝胶时使用的引发条件而显著变化，高单体浓度溶液。已经使用实时动态流变学和脉冲 NMR/MRI 的独特互补组合来研究氧化还原引发系统的组成对凝胶化过程和水凝胶性能的影响。过硫酸盐引发剂与叔胺活化剂的摩尔比会影响聚合动力学、形态和水凝胶的机械性能。我们进一步表明，活化剂占主导地位的体系往往会产生具有较高储能模量和较低吸水率的水凝胶。这种趋势归因于交联度的增加。从 NCH 和没有有机交联剂制备的水凝胶的水状态分析中得出结论，粘土片层没有与聚合物分子形成共价键，但有助于形成物理网络。在高单体浓度下进行丙烯酰胺聚合时，存在聚合物链自交联的证据。引发系统的组成会影响形成的自交联数量。
