Developing Multi Stimuli-Responsive Core/Shell Microcapsules to Control the Release of Volatile Compounds

Encapsulation of 2-oxoacetates into poly(urea-urethane) core/shell microcapsules allows the light-induced controlled release of volatile compounds such as fragrances, plant volatiles, pheromones, or other semiochemicals. On exposure to UVA light, 2-oxoacetates decompose to form a carbonyl compound together with CO2 or CO, which can build overpressure inside the capsules that expands and/or cleaves the capsule wall to release its content. The influence of the structure and ratio of the polyisocyanates and diamines used for interfacial polymerization, as well as the composition of the capsule wall and the oil phase, are investigated by dynamic headspace analysis of the released volatile compounds to optimize the performance of the delivery system. The combination of a light-induced release with the mechanical cleavage of the capsule gives access to multi stimuli-responsive systems that selectively respond to the different triggers applied. Furthermore, the concept outlined in the present work is generally applicable to other photolabile precursors that generate a gas inside the capsules and thus release co-encapsulated active molecules as a direct response to light.