杂化双网络水凝胶屈服的机制起源
Mechanistic Origins of Yielding in Hybrid Double Network Hydrogels
AI总结：
本文通过系统调控杂化双网络水凝胶网络内外相互作用并结合LAOS表征，揭示其两步屈服分别源于网络间作用与瞬态网络内部作用。
摘要：
杂化双网络水凝胶是一类由瞬态交联和永久交联聚合物网络构成的材料，表现出增强的韧性，而这种韧性被认为由瞬态聚合物网络的屈服所控制。两种聚合物网络在该屈服转变中的确切作用及其相互作用仍是一个悬而未决的问题；我们在此通过构建一系列水凝胶设计来解决这一问题，在这些设计中，两个聚合物网络内部及彼此之间的相互作用被系统性地抑制或增强。我们使用大振幅振荡剪切流变学（LAOS）表征每一种水凝胶设计。通过考察不同水凝胶设计中由弹性应力反映的屈服，我们阐明杂化双网络水凝胶表现出两步屈服行为，该行为源于瞬态交联的存在。通过检查每个振荡周期内以及不同水凝胶设计之间的流变响应，我们表明瞬态网络中的微结构变化在该屈服的第二阶段至关重要。通过系统性改变相互作用强度，我们推测屈服的第一步由两个聚合物网络之间的分子间相互作用决定。这些相互作用也会影响屈服的第二步，而我们证明第二步由聚合物网络内部的瞬态分子间相互作用控制。因此，我们的研究揭示，聚合物网络之间的相互作用与网络内部的相互作用同样关键，并为如何识别、调节和控制软复合材料中的屈服机制提供了洞见。
英文摘要：
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.
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