Ministry of Education Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China.
Hangzhou Toka Ink Co., Ltd., Hangzhou 310018, China.
J Mater Chem B. 2021 Dec 15;9(48):9863-9873. doi: 10.1039/d1tb02114a.
Revealing the relationship between network topologies and mechanical properties of hydrogels is fundamental yet challenging in the design of tough soft materials. Here, we report a series of hydrogels using -isopropyl acrylamide (NIPAm) and acrylic acid (AAc) as the basic units to form a single network of the copolymer, a semi-interpenetrated network of two homopolymers, and a grafted network with homopolymer chains anchored on another homopolymer network, to investigate the influence of network architectures on the mechanical properties and thermal responses of the gels. We found that the properties of the gels are also significantly influenced by the formation of hydrogen bonds between poly(-isopropyl acrylamide) (PNIPAm) and poly(acrylic acid) (PAAc) segments. The gels with the single network of poly(NIPAm--AAc) are mechanically weak due to the low efficiency for forming robust hydrogen bonds, while micro-segregated domains are formed in the hydrogels with a semi-interpenetrated network structure due to the formation of inter-chain hydrogen bonds that favors energy dissipation and toughening of the gels. On the other hand, dense hydrogen bonds form between the grafted PNIPAm chains and the PAAc network, resulting in nano-segregated domains and excellent mechanical properties of the gels. The hydrogels with the grafted network structure exhibit a more repeatable response to temperature than those with the semi-interpenetrated network structure due to the relatively stable hydrogen-bond network. The comparison of the mechanical properties and thermal stability of the hydrogels with the same composition but different topological networks should be informative for engineering hydrogel properties or functions by tailoring the network structures.
揭示水凝胶的网络拓扑结构与力学性能之间的关系对于坚韧软物质的设计具有基础且重要的意义。在这里，我们报告了一系列使用异丙基丙烯酰胺（NIPAm）和丙烯酸（AAc）作为基本单元的水凝胶，形成了共聚物的单网络、两种均聚物的半互穿网络以及带有均聚物链锚定在另一个均聚物网络上的接枝网络，以研究网络结构对凝胶力学性能和热响应的影响。我们发现，凝胶的性质也受到聚（异丙基丙烯酰胺）（PNIPAm）和聚（丙烯酸）（PAAc）段之间氢键形成的显著影响。由于形成强氢键的效率较低，具有聚（NIPAm-AAc）单网络的凝胶力学性能较弱，而具有半互穿网络结构的水凝胶由于形成有利于能量耗散和增韧的链间氢键，形成了微相分离的畴。另一方面，接枝的 PNIPAm 链与 PAAc 网络之间形成密集的氢键，导致凝胶形成纳米相分离域和优异的力学性能。由于氢键网络相对稳定，具有接枝网络结构的水凝胶对温度的响应比具有半互穿网络结构的水凝胶更具可重复性。具有相同组成但拓扑网络不同的水凝胶的力学性能和热稳定性的比较，对于通过调整网络结构来设计水凝胶的性能或功能应该是有启发性的。
