Squeezing release mechanism of encapsulated compounds from photo-sensitive microcapsules

Controlled release of photo-triggered systems is widely investigated due to its enormous functional applications, but only a few reports describing a mechanism of this phenomenon have been published. To provide a mechanism of active material release from photo-sensitive microcapsules based on cross-linked liquid crystalline polyamide containing azobenzene moieties incorporated in the main chain, we performed quantum chemical calculations. By optimizing structure of trans and cis isomers of azobenzene molecule we were able to show that its trans-to-cis isomerization is responsible for release of encapsulated material. Computational investigation demonstrated that the polymeric main chain length forming the capsule shell decreases approximately 28% in comparison to the initial state by trans–cis isomerization of azobenzene moieties. Moreover, the photo-isomerization of azobenzene molecules was experimentally confirmed by Fourier Transform Infrared Spectroscopy (FTIR) and its influence on capsule morphology was monitored by Atomic Force Microscopy (AFM). Finally, based on theoretical and experimental data a mechanism of encapsulated active release from capsule shells was proposed.