Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven, The Netherlands.
École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI) ParisTech, UMR 7615, 10, Rue Vauquelin, 75231 Paris Cédex 05, France and CNRS, UMR 7615, 10, Rue Vauquelin, 75231 Paris Cédex 05, France and Sorbonne-Universités, Université Pierre et Marie Curie (UPMC) Université Paris 06, UMR 7615, 10, Rue Vauquelin, 75231 Paris Cédex 05, France.
Soft Matter. 2019 Mar 6;15(10):2190-2203. doi: 10.1039/c8sm02577k.
Reversible crosslinking is a design paradigm for polymeric materials, wherein they are microscopically reinforced with chemical species that form transient crosslinks between the polymer chains. Besides the potential for self-healing, recent experimental work suggests that freely diffusing reversible crosslinks in polymer networks, such as gels, can enhance the toughness of the material without substantial change in elasticity. This presents the opportunity for making highly elastic materials that can be strained to a large extent before rupturing. Here, we employ Gaussian chain theory, molecular simulation, and polymer self-consistent field theory for networks to construct an equilibrium picture for how reversible crosslinks can toughen a polymer network without affecting its elasticity. Maximisation of polymer entropy drives the reversible crosslinks to bind preferentially near the permanent crosslinks in the network, leading to local molecular reinforcement without significant alteration of the network topology. In equilibrium conditions, permanent crosslinks share effectively the load with neighbouring reversible crosslinks, forming multi-functional crosslink points. The network is thereby globally toughened, while the linear elasticity is left largely unaltered. Practical guidelines are proposed to optimise this design in experiment, along with a discussion of key kinetic and timescale considerations.
可逆交联是一种聚合物材料的设计范式，其中通过在聚合物链之间形成瞬态交联的化学物质对其进行微观增强。除了自我修复的潜力外，最近的实验工作表明，在聚合物网络（如凝胶）中自由扩散的可逆交联可以在不显著改变弹性的情况下提高材料的韧性。这为制造具有高弹性的材料提供了机会，这些材料在破裂之前可以被拉伸到很大的程度。在这里，我们使用高斯链理论、分子模拟和聚合物自洽场理论来构建网络的平衡图景，以了解可逆交联如何在不影响其弹性的情况下增强聚合物网络的韧性。聚合物熵的最大化促使可逆交联优先结合在网络中的永久交联附近，从而在不显著改变网络拓扑结构的情况下实现局部分子增强。在平衡条件下，永久交联与相邻的可逆交联有效地分担负载，形成多功能交联点。因此，网络得到了全局增强，而线性弹性基本保持不变。本文提出了优化实验设计的实用指南，并讨论了关键的动力学和时间尺度考虑因素。
