Ribeiro de Souza Lívia, Al-Tabbaa Abir
Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK.
Lab Chip. 2021 Nov 25;21(23):4652-4659. doi: 10.1039/d1lc00569c.
Capsule-based self-healing of cementitious materials is an effective way of healing cracks, significantly extending the life of structures, without imposing changes due to the incorporation of capsules into products during mixing. The methodologies currently being used for the development of capsules with a liquid core as a healing agent yield a wide range of sizes and shell thicknesses for the microcapsules, preventing a detailed assessment and optimisation of the microcapsule size and its effects. Uniquely, microfluidic technology offers precise control over the size and shell thickness through the formation of double emulsions. The drawback is that only small quantities of material can be typically produced. Here, by using paralleled junctions in a microfluidic device, high throughput production of materials was achieved, focusing for the first time on self-healing of cementitious materials. A microfluidic chip was assembled with 4 channels in parallel and selected hydrophobicity for the formation of the double emulsions. A coefficient of variation below 2.5% was observed for the 4 junctions, demonstrating the formation of monodisperse capsules. The control over the size and shell thickness by adjusting the flow rates was demonstrated, yielding capsules with an outer diameter of 615-630 μm and a shell thickness varying between 50 and 127 μm. By using triethanolamine as a surfactant, capsules with an aqueous core were produced. Furthermore, by selecting PEA, an acrylate with low tensile strength, the capsules embedded in the cement paste were successfully triggered to release the healing agent by crack formation. Capsules were successfully produced continuously for 7 h, with inner and outer diameters of 500 ± 31 μm and 656 ± 9 μm at a production rate of ∼13 g h and a yield of around 80%. With these results and considering up to 6 chips in parallel, the production rate could be up to 1.5 kg per day. This demonstrates the huge potential of the microfluidic device with unique features to produce sufficiently large quantities of microcapsules for laboratory-scale assessment of self-healing performance.
基于胶囊的胶凝材料自修复是一种有效的裂缝修复方法，可显著延长结构寿命，且在混合过程中不会因加入胶囊而对产品造成改变。目前用于开发以液体为修复剂的核心胶囊的方法，会产生各种尺寸和壳厚度的微胶囊，阻碍了对微胶囊尺寸及其效果的详细评估和优化。独特的是，微流控技术通过形成双重乳液，能对尺寸和壳厚度进行精确控制。缺点是通常只能生产少量材料。在此，通过在微流控装置中使用平行连接，实现了材料的高通量生产，首次聚焦于胶凝材料的自修复。组装了一个具有4个平行通道的微流控芯片，并选择了疏水性以形成双重乳液。观察到4个连接点的变异系数低于2.5%，证明形成了单分散胶囊。通过调节流速展示了对尺寸和壳厚度的控制，得到外径为615 - 630μm、壳厚度在50至127μm之间变化的胶囊。通过使用三乙醇胺作为表面活性剂，制备了具有水相核心的胶囊。此外，通过选择拉伸强度低的丙烯酸酯PEA，嵌入水泥浆体中的胶囊在裂缝形成时成功触发释放修复剂。连续7小时成功生产胶囊，内径和外径分别为500±31μm和656±9μm，生产率约为13 g/h，产率约为80%。基于这些结果并考虑最多6个芯片并行，生产率可达每天1.5 kg。这证明了具有独特特性的微流控装置在生产足够大量微胶囊用于自修复性能实验室规模评估方面的巨大潜力。
