Effect of sticker clustering on the dynamics of associative networks
Effect of sticker clustering on the dynamics of associative networks
复制标题
贴纸聚类对关联网络动态的影响
DOI：
10.1039/d1sm00392e
复制
发表时间：
2021
期刊：
影响因子：
3.4
通讯作者：
Olsen, Bradley D.
中科院分区：
文献类型：
--
作者：
Mahmad Rasid, Irina;Do, Changwoo;Holten-Andersen, Niels;Olsen, Bradley D.
最近的实验和理论工作表明，粘贴聚类可以用来提高性能，如韧性和抗蠕变性的聚合物网络。虽然很明显属性的变化与网络拓扑的变化有关，但其机制关系仍然没有得到很好的理解。在这项工作中，贴纸集群的效果进行了研究，通过比较无规共聚物的动力学与那些贴纸聚集在链的末端，在未纠缠的制度，使用线性力学和扩散测量。采用可逆加成-断裂链转移（RAFT）聚合法合成了N，N-二甲基丙烯酰胺（DMA）与组氨酸侧基的共聚物。使用双官能RAFT试剂合成簇合物，使得中间嵌段由PDMA组成，并且两个末端嵌段是DMA和组氨酸官能化单体的无规共聚物。加入镍离子后，瞬时金属配位交联形成为组氨酸-镍络合物。流变学，中子散射和自扩散测量强迫瑞利散射相结合的研究揭示了网络拓扑结构和应力松弛模式的变化。提出的网络拓扑结构由非缔合中间块桥接的组氨酸-Ni络合物的聚集体组成。因此，应力松弛需要多个键的协同解离，导致松弛时间增加。然而，增加的弛豫时间伴随着更快的扩散。这是由于存在缺陷，如弹性不活跃的链环。这项研究表明，合作贴纸解离的影响，可以观察到，即使在存在一个显着的分数的环缺陷，这是已知的改变传统的遥爪聚合物的非线性特性。
Recent experimental and theoretical work has shown that sticker clustering can be used to enhance properties such as toughness and creep resistance of polymer networks. While it is clear that the changes in properties are related to a change in network topology, the mechanistic relationship is still not well understood. In this work, the effect of sticker clustering was investigated by comparing the dynamics of random copolymers with those where the stickers are clustered at the ends of the chain in the unentangled regime using both linear mechanics and diffusion measurements. Copolymers of N,N-dimethyl acrylamide (DMA) and pendant histidine groups were synthesized using reversible addition–fragmentation chain transfer (RAFT) polymerization. The clustered polymers were synthesized using a bifunctional RAFT agent, such that the midblock consisted of PDMA and the two end blocks were random copolymers of DMA and the histidine-functionalized monomer. Upon addition of Ni ions, transient metal-coordinate crosslinks are formed as histidine–Ni complexes. Combined studies of rheology, neutron scattering and self-diffusion measurements using forced Rayleigh scattering revealed changes to the network topology and stress relaxation modes. The network topology is proposed to consist of aggregates of the histidine–Ni complexes bridged by the non-associative midblock. Therefore, stress relaxation requires the cooperative dissociation of multiple bonds, resulting in increased relaxation times. The increased relaxation times, however, were accompanied by faster diffusion. This is attributed to the presence of defects such as elastically inactive chain loops. This study demonstrates that the effects of cooperative sticker dissociation can be observed even in the presence of a significant fraction of loop defects which are known to alter the nonlinear properties of conventional telechelic polymers.