Explosive Raspberries: Controlled Magnetically Triggered Bursting of Microcapsules

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Abstract
On‐demand and spatially controlled release of active components is crucial in several applications ranging from medicine to food and agriculture. Although many encapsulation approaches have been developed to address specific application‐related boundary conditions, microcapsule systems that enable quick and site‐specific release are still highly demanded. Here, a new design for a magnetically triggered release system consisting of an inductively heatable core covered by temperature‐sensitive bursting microcapsules is proposed. Release of the microcapsule content is achieved within a few seconds by a locally induced thermal shock without overheating the surrounding matrix. The bursting microcapsules are produced from monodisperse double emulsion templates made by microfluidics. The microcapsule shell structure is heterogeneous, consisting of a polymer particle network wetted by a liquid blowing agent and sealed by a polymeric skin. Steel particles (1 mm) are selected as an exemplary heat source because of their fast temperature increase through magnetic induced heating. Proof‐of‐concept microbursting experiments are performed to demonstrate the efficacy of the proposed raspberry design in achieving controlled local release using a magnetic trigger. In this study, it is shown that the system can be applied for the on‐demand setting of cementitious materials by externally triggering the release of a cement accelerator without undesired excessive heating of the matrix.

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