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Enhanced Mixing of Microvascular Self-Healing Reagents Using Segmented Gas–Liquid Flow

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posted on 12.09.2018, 22:14 by Leon M. Dean, Brett P. Krull, Kevin R. Li, Yelizaveta I. Fedonina, Scott R. White, Nancy R. Sottos
Microvascular self-healing systems have previously been demonstrated to restore large-scale damage and achieve repeated healing of multiple damage events in polymers. However, the healing performance of these systems is often limited because the laminar nature of flow in microchannels  results in poor mixing of two-part self-healing reagents. In this paper, we introduce segmented gas–liquid flow (SGLF) to enhance the mixing of reagents in microvascular self-healing systems. In SGLF, discrete liquid slugs containing self-healing reagents are separated by gas bubbles while flowing through a single microchannel. Recirculating streamlines within the liquid slugs can enhance the mixing of miscible liquids such as healing reagents. We investigate the effect of SGLF on mixing and healing for a two-stage chemistry used to restore large-scale damage in thermoset polymers. Additionally, we employ SGLF to deliver an epoxy–thiol chemistry, enabling the repeated recovery of fracture toughness in glass fiber-reinforced composites. In both systems, the mixing of healing agents delivered by SGLF is enhanced compared to alternative microvascular delivery strategies. For the two-stage chemistry, SGLF increases the maximum damage size that can be healed by 25% compared to laminar single-phase flow. Furthermore, there are concomitant increases in the extent of polymerization and the mechanical properties of the restored material, including a fivefold increase in the peak load sustained during a push-out test. For the epoxy–thiol chemistry, SGLF enables multiple healing cycles with healing efficiency above 100%. On the basis of these results, we envision that SGLF could improve performance for a variety of microvascular self-healing systems with different host materials, damage modes, and healing chemistries.