Fredi Giulia, Simon Frank, Sychev Dmitrii, Melnyk Inga, Janke Andreas, Scheffler Christina, Zimmerer Cordelia
Department of Industrial Engineering, University of Trento, Via Sommarive 9, I-38123 Trento, Italy.
Leibniz-Institut für Polymerforschung, Hohe Straße 6, D-01069 Dresden, Germany.
ACS Omega. 2020 Jul 31;5(31):19639-19653. doi: 10.1021/acsomega.0c02271. eCollection 2020 Aug 11.
Microencapsulated phase change materials (PCMs) are attracting increasing attention as functional fillers in polymer matrices, to produce smart thermoregulating composites for applications in thermal energy storage (TES) and thermal management. In a polymer composite, the filler-matrix interfacial adhesion plays a fundamental role in the thermomechanical properties. Hence, this work aims to modify the surface of commercial PCM microcapsules through the formation of a layer of polydopamine (PDA), a bioinspired polymer that is emerging as a powerful tool to functionalize chemically inert surfaces due to its versatility and great adhesive potential in many different materials. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) evidenced that after PDA coating, the surface roughness increased from 9 to 86 nm, which is beneficial, as it allows a further increase in the interfacial interaction by mechanical interlocking. Spectroscopic techniques allowed investigating the surface chemistry and identifying reactive functional groups of the PDA layer and highlighted that, unlike the uncoated microcapsules, the PDA layer is able to react with oxirane groups, thereby forming a covalent bond with the epoxy matrix. Hot-stage optical microscopy and differential scanning calorimetry (DSC) highlighted that the PDA modification does not hinder the melting/crystallization process of the paraffinic core. Finally, SEM micrographs of the cryofracture surface of epoxy composites containing neat or PDA-modified microcapsules clearly evidenced improved adhesion between the capsule shell and the epoxy matrix. These results showed that PDA is a suitable coating material with considerable potential for increasing the interfacial adhesion between an epoxy matrix and polymer microcapsules with low surface reactivity. This is remarkably important not only for this specific application but also for other classes of composite materials. Future studies will investigate how the deposition parameters affect the morphology, roughness, and thickness of the PDA layer and how the layer properties influence the capsule-matrix adhesion.
微胶囊相变材料（PCM）作为聚合物基体中的功能填料，在生产用于热能存储（TES）和热管理应用的智能温度调节复合材料方面正受到越来越多的关注。在聚合物复合材料中，填料与基体之间的界面附着力对热机械性能起着至关重要的作用。因此，本工作旨在通过形成一层聚多巴胺（PDA）来修饰商用PCM微胶囊的表面，聚多巴胺是一种受生物启发的聚合物，由于其多功能性以及在许多不同材料中具有巨大的粘附潜力，正成为一种使化学惰性表面功能化的强大工具。扫描电子显微镜（SEM）和原子力显微镜（AFM）证明，在涂覆PDA后，表面粗糙度从9纳米增加到86纳米，这是有益的，因为它可以通过机械互锁进一步增强界面相互作用。光谱技术能够研究表面化学并识别PDA层的反应性官能团，并突出表明，与未涂覆的微胶囊不同，PDA层能够与环氧基团反应，从而与环氧基体形成共价键。热台光学显微镜和差示扫描量热法（DSC）突出表明，PDA改性不会阻碍石蜡芯的熔化/结晶过程。最后，含有纯微胶囊或PDA改性微胶囊的环氧复合材料冷冻断裂表面的SEM显微照片清楚地证明了胶囊壳与环氧基体之间的附着力得到了改善。这些结果表明，PDA是一种合适的涂层材料，在提高环氧基体与表面反应性低的聚合物微胶囊之间的界面附着力方面具有相当大的潜力。这不仅对于这种特定应用非常重要，而且对于其他类别的复合材料也非常重要。未来的研究将探讨沉积参数如何影响PDA层的形态、粗糙度和厚度，以及层的性质如何影响胶囊与基体的附着力。
