Design of millimeter-scale microwave-induced capsules and their non-instantaneous release

In recent years, many studies have been carried out on the release system induced by the microwave signal, featured with great thermal efficiency and high penetration. However, studies on microwave responsive system on millimeter length scale are limited, which is of great importance due to its high loading capacity and widespread application. In this study, novel microwave-induced capsules on millimeter length scale with responsiveness in water-free environment, consisting of paraffin shell and the supportive skeleton fibers were designed and prepared. The detailed microwave-induced releasing behaviors, together with the morphology, loading capacity of capsules were systematically investigated. Non-instantaneous releasing behavior consisted of microwave heating, shell melting and core releasing was observed, and was supported by numerical simulations. The key role of paraffin shell with different thickness was confirmed in the kinetics of releasing. The release profile can be well described by a two-segment model, which includes zero-order model and cumulative distribution functions, corresponding to diffusion controlled and shell-melting controlled releasing processes, respectively.