Tunable mechanical properties of PDMS–TMPTMA microcapsules for controlled release in coatings

Abstract

Within coating formulations, microcapsules serve as vehicles for delivering compounds like catalysts and self-healing agents. Designing microcapsules with precise mechanical characteristics is crucial to ensure their contents' timely release and minimize residual shell fragments, thereby avoiding adverse impacts on the coating quality. With these constraints in mind, we explored the use of 1 cSt PDMS oil as a diluent (porogen) in trimethylolpropane trimethacrylate (TMPTMA)-based to fabricate microcapsules with customized mechanical properties and submicrometer debris size after shell breakup that can encapsulate a wide range of compounds. Microcapsules were fabricated from double emulsion templates featuring an aqueous core and shells with different PDMS : TMPTMA volume percent ratios. Their mechanical properties under compression and their capacity for encapsulation were characterized. PDMS : TMPTMA ratios exceeding 20 : 80 caused phase separation during crosslinking, leading to a porous shell structure of TMPTMA clusters. The strength of the microcapsules decreased as the PDMS:TMPTMA ratio increased, with ratios above 30 : 70 resulting in mechanically fragile microcapsules fracturing into fragments <10 μm in size. Microcapsules produced with a 0 : 100 PDMS : TMPTMA ratio exhibited strong mechanical properties and were capable of encapsulating small volatile compounds like 1,4-diazabicyclo[2.2.2]octane (a catalyst), while those with ratios >30 : 70 were only suitable to encapsulate larger molecules. The combination of PDMS:TMPTMA chemistry and the precise control provided by the double emulsion generation process in microcapillary devices makes PDMS:TMPTMA a versatile system suitable for various pressure-sensitive encapsulation applications.