Taniguchi Takuro, Urayama Kenji
Department of Macromolecular Science and Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan.
Gels. 2021 Jun 14;7(2):71. doi: 10.3390/gels7020071.
We investigated the linear dynamic viscoelasticity of dual cross-link (DC) poly(vinyl alcohol) (PVA) (DC-PVA) hydrogels with permanent and transient cross-links. The concentrations of incorporated borate ions to form transient cross-links in the DC-PVA hydrogels () were determined by the azomethine-H method. The dynamic viscoelasticity of the DC-PVA hydrogel cannot be described by a simple sum of the dynamic viscoelasticity of the PVA gel with the same permanent cross-link concentration and the PVA aqueous solution with the same borate ion concentration ( = ) as in the DC-PVA gel. The DC-PVA hydrogel exhibited a considerably higher relaxation strength, indicating that the introduction of permanent cross-links into temporary networks increases the number of viscoelastic chains with finite relaxation times. In contrast, the relaxation frequency () (given by the frequency at the maximum of loss modulus) for the DC-PVA hydrogel was slightly lower but comparable to that for a dilute PVA solution with the same . This signifies that the relaxation dynamics of the DC-PVA hydrogels is essentially governed by the lifetime of an interchain transient cross-link (di-diol complex of boron). The effect of permanent cross-linking on the relaxation dynamics was observed in the finite broadening of the relaxation-time distribution in the long time region.
我们研究了具有永久性和瞬态交联的双交联（DC）聚乙烯醇（PVA）（DC-PVA）水凝胶的线性动态粘弹性。通过甲亚胺-H法测定了DC-PVA水凝胶中用于形成瞬态交联的硼酸根离子的掺入浓度（）。DC-PVA水凝胶的动态粘弹性不能用具有相同永久交联浓度的PVA凝胶和具有与DC-PVA凝胶中相同硼酸根离子浓度（=）的PVA水溶液的动态粘弹性的简单总和来描述。DC-PVA水凝胶表现出相当高的松弛强度，这表明在临时网络中引入永久交联会增加具有有限松弛时间的粘弹性链的数量。相比之下，DC-PVA水凝胶的松弛频率（）（由损耗模量最大值处的频率给出）略低，但与具有相同的稀PVA溶液的松弛频率相当。这表明DC-PVA水凝胶的松弛动力学基本上由链间瞬态交联（硼的二醇络合物）的寿命控制。在长时间区域中松弛时间分布的有限展宽中观察到了永久交联对松弛动力学的影响。
