Abstract
ABSTRACTSiO2-based microcapsules containing hydrophobic molecules exhibited potential applications such as extrinsic self-healing, drug delivery, due to outstanding thermal and chemical stability of SiO2. However, to construct SiO2-based microcapsules with both high encapsulation loading and long-term structural stability is still a troublesome issue, limiting their further utilization. We herein design a single-batch route, a combined interfacial and in-situ polymerization strategy, to fabricate epoxy-containing SiO2-based microcapsules with both high encapsulation loading and long-term structural stability. The final SiO2-based microcapsules preserve high encapsulation loading of 85.7 wt% by controlling exclusively hydrolysis and condensed polymerization at oil/water interface in the initial interfacial polymerization step. In the subsequent in-situ polymerization step, the initial SiO2-based microcapsules as seeds could efficiently harvest SiO2 precursors and primary SiO2 particles to finely tune the SiO2 wall thickness, thereby enhancing long-term structural stability of the final SiO2-based microcapsules including high thermal stability with almost no any weight loss until 250°C, and strong tolerance against nonpolar solvents such as CCl4 with almost unchanged core-shell structure and unchanged core weight after immersing into strong solvents for up to 5 days. These SiO2-based microcapsules are extremely suited for processing them into anticorrosive coating in the presence of nonpolar solvents for self-healing application.
Highlights
Microencapsulation of liquid functional ingredients in solid shell has recently drawn great attention owing to its various applications in self-healing, drug delivery, and energy-storage fields in the past decades [1,2,3,4]
Bisphenol A diglycidyl ether has similar solubility parameter (23.4 MPa1/2) [22] to that of tetraethyl orthosilicate (TEOS), SiO2 precursor (16.4 MPa1/ 2) [23], meaning that their good compatibility is intrinsically favored for designing an interfacial polymerization strategy to synthesize epoxy resin-containing SiO2 microcapsules
In the interfacial polymerization step, firstly, epoxy resin E-51, epoxy resin A1815, and TEOS could be uniformly mixed as oil phase in terms of their similar solubility parameters, and the mixture was emulsified in aqueous F127 solution to form a stable O/W emulsion (Figure 1(b))
Summary
Microencapsulation of liquid functional ingredients in solid shell has recently drawn great attention owing to its various applications in self-healing, drug delivery, and energy-storage fields in the past decades [1,2,3,4] Microcapsules could both isolate inner active species with high loading from outer environment and hold. General strategies to encage hydrophobic molecules into SiO2-based microcapsules in O/W emulsion are mainly divided into two classes: interfacial polymerization [14,15,16] and in-situ polymerization [17,18,19] The difference between these two mechanisms lies in the diffusion of hydrophobic SiO2 precursors from either the inner oil phase or the outer water phase onto the interface of emulsion drops to achieve the sol-gel deposition of SiO2 shell catalyzed by aqueous acid or alkali solution.
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