Investigation of performance of active microcapsule actuation

Microcapsules are micron-sized hollow particles that can be synthesized with fluid encapsulated in the interior. The microcapsules can be used as a potential actuation technique by incorporating stimulus-responsive materials, such as permselective, light-sensitive and electrically sensitive materials. The microcapsules range from 10 to 80 microns in diameter and wall thickness normalized to radius might range from 0.05 to 0.5. The actuation concept is to control the size of the microcapsules by varying the interior fluid pressure using an external stimulus. This paper presents efforts to model the performance and capabilities of microcapsules as micro actuators. We assume the pressure of the fluid inside of the microcapsules can be controlled by certain technique, such as thermal, electro or optical stimulus to the fluid. This paper will focus at modeling the performance of microcapsules under known pressure variation of fluid inside. First the paper compares a thin-wall model to a thick-wall model and identifies that thin-wall theory is not accurate enough for microcapsules. Simulation results show that energy density in the order of 3J/cm³ is theoretically achievable for thick microspheres. Two type of materials are studied as the materials encapsulated in microcapsules. Their constitutive equations are then incorporated into the thick-wall model. Simulations show hydrocarbon solvents are much more efficient than ideal gas in terms of actuation performance.