标题： 混合双网络水凝胶屈服的机制起源 显示英文标题

标题： Mechanistic Origins of Yielding in Hybrid Double Network Hydrogels

摘要： 混合双网络水凝胶是一类由瞬时和永久交联的聚合物网络组成的材料，表现出增强的韧性，这种韧性被认为是由瞬时聚合物网络的屈服所控制的。 这两个聚合物网络在这一屈服转变中的精确作用及其相互作用仍然是一个开放性问题，我们通过构建一系列水凝胶设计来解决这个问题，在这些设计中，两个聚合物网络内部及之间的相互作用被系统地抑制或增强。 我们使用大振幅振荡剪切流变学（LAOS）对每种水凝胶设计进行表征。 通过弹性应力检查不同水凝胶设计中的屈服现象，我们阐明了混合双网络水凝胶表现出两步屈服行为，这源于瞬时交联的存在。 检查每个振荡周期内的流变响应以及不同水凝胶设计之间的响应，我们表明瞬时网络中的微观结构变化在这一屈服的第二阶段中起着关键作用。 我们认为，屈服的第一步是由两种聚合物网络之间的分子间相互作用决定的，我们通过系统地改变相互作用的强度来验证这一点。 这些相互作用也影响屈服的第二步，我们表明这一步是由聚合物网络内的瞬时分子间相互作用所控制的。 因此，我们的研究揭示了聚合物网络之间的相互作用与聚合物网络内部的相互作用一样重要，从而为如何识别、调整和控制软复合材料中的屈服机制提供了见解。 显示英文摘要

摘要： Hybrid double-network hydrogels are a class of material that comprise transiently and permanently crosslinked polymer networks and exhibit an enhanced toughness that is believed to be governed by the yielding of the transient polymer network. The precise role of the two polymer networks in this yielding transition and their interplay remains an open question that we address here through constructing a series of hydrogel designs in which the interaction within and between the two polymer networks are systematically inhibited or enhanced. We characterise each of the hydrogel designs using large amplitude oscillatory shear rheology (LAOS). Inspecting yielding through elastic stress across hydrogel designs, we elucidate that the hybrid double-network hydrogel exhibits a two-step yielding behaviour that originates from to the presence of transient crosslinks. Examining the rheological response within each oscillatory cycle and across the hydrogel designs, we show that the micro-structural changes in the transient network are crucial in the second stage of this yielding. We surmise that the first step of yielding is determined by the intermolecular interactions between the two polymer networks by systematically altering the strength of the interactions. These interactions also influence the second step of yielding, which we show is governed by the transient intermolecular interactions within the polymer networks. Our study therefore reveals that the interactions between the polymer networks are as crucial as within the polymer networks and therefore provides insights into how the yielding mechanisms in soft composite materials can be identified, adjusted, and controlled.