Design, Collapse and Mixing of Nanoreactors for In Situ TEM Imaging of Confined Reactions in Liquids

Nanocapsules are hollow nanoscale shells that have applications in drug delivery, batteries, self-healing materials, and as model systems for naturally occurring shell geometries. In many applications, nanocapsules are designed to release their cargo as they buckle and collapse, but the details of this transient buckling process have not been directly observed. Here we use <i>in situ</i> liquid phase transmission electron microscopy to record the mixing of lipid nanocapsules and the electron-irradiation-induced buckling in spherical polymer capsules. We observe in real time the release of aqueous cargo from these nanocapsules and their buckling into morphologies with single or multiple indentations. The <i>in situ</i> buckling of nanoscale capsules is compared to <i>ex situ</i> measurements of collapsed and micrometer-sized capsules and to Monte Carlo (MC) simulations. The shape and dynamics of the collapsing nanocapsules are consistent with MC simulations. Our experiments suggest design rules for nanocapsules with desired buckling response based on parameters such as capsule radius, wall thickness, and collapse rate.