Amine holds great potential as an ideal CO₂ adsorbent and versatile curing agent for various adhesives for high-end industrial applications. Encapsulating amine into microstructures promotes designing smart material systems with high adaptability, controllability, and high efficiency. In recent years, researchers have been making increasing efforts in microencapsulating amine with various techniques. However, the efficient encapsulation of amines was impeded due to their extremely high reactivity towards various groups and good solubility in most solvents, which made it difficult to form stable emulsions during encapsulation. The primary objective of this thesis is to address these challenges by exploring and developing effective strategies for scalable amine encapsulation with desirabl...[ Read more ]

Amine holds great potential as an ideal CO₂ adsorbent and versatile curing agent for various adhesives for high-end industrial applications. Encapsulating amine into microstructures promotes designing smart material systems with high adaptability, controllability, and high efficiency. In recent years, researchers have been making increasing efforts in microencapsulating amine with various techniques. However, the efficient encapsulation of amines was impeded due to their extremely high reactivity towards various groups and good solubility in most solvents, which made it difficult to form stable emulsions during encapsulation. The primary objective of this thesis is to address these challenges by exploring and developing effective strategies for scalable amine encapsulation with desirable ultimate properties, including high core content, good shell strength, thermal stability, chemical stability, etc.

Inspired by the steady control of material interchange through the cell membrane, we designed a strategy to overcome the difficulties the rapid interfacial polymerization brings to the encapsulation system. A permeable hollow poly(urea-formaldehyde) (PUF) microcapsules were firstly prepared. Then the amine was infiltrated under vacuum into the PUF hollow structures for further interfacial polymerization to seal the pores. This strategy effectively solves the problem of emulsion breakup during the shell forming process. Thus, the microcapsules with high core content and high shell properties could be produced in a scalable manner.

We further simplified the strategy by in-situ formation of microporous acrylonitrile butadiene styrene (ABS) shell enwrapping the amine droplets for further steady interfacial polymerization. Unlike previous emulsion-based attempts which associated the success of encapsulation with high emulsion stability, the emulsion was not necessarily thermodynamically stable, but underwent a transient quasi-equilibrium process to allow steady shell-forming polymer deposition. The ‘membrane’ made of ABS robustly protected the microcapsules from destructive forces including interfacial reaction kinetics and microcapsules collisions. Moreover, it is inspiring to generate microcapsules with customized features for various applications in one setup. It is believed this successful exploration offers both academic merits for interfacial behavior of the nonaqueous emulsions and new insights into integrated encapsulation systems for diversified demands.

In the third part, we integrated the direct extrusion using a microfluidic device with the fast interfacial polymerization. The competition between the shear-induced fluid breakup and the liquid thread retaining by the rapidly formed polyurea shell resulted in the microcapsules with tunable aspect ratios. Moreover, the amine molecules reacted with the diisocyanate monomers instantly once the amine liquid was injected into the continuous phase, avoiding the emulsification problem brought by the conventional technique. The polyurea interfacial polymerization mechanism was also studied concerning shell-forming and morphology evolution. Based on the understanding of fluid jet breakup and interfacial polymerization mechanism, microcapsules with tunable features were prepared for further applications.

Finally, the promising potential of these amine-loaded microcapsules in various applications including self-healing carbon fiber reinforced polymers (CFRPs), polyurea-based instant adhesives, and CO₂ adsorbents was demonstrated preliminarily. Moreover, we verified experimentally the higher self-healing efficiency of tubular microcapsules compared to the spherical counterparts for the first time in literature. These explorations offer a new perspective for both diverse polar payload assembling and versatile applications thereof.