Preparation of multilayer microcapsules encapsulating aqueous lithium bromide and their mechanical stability

The development of more efficient and reliable absorption/adsorption refrigeration for air conditioners (ACs) and chillers is of great interest due to the increasing demand of these cooling devices in homes and offices. Presently, the majority of the ACs incorporate aqueous lithium salts as both refrigerate and desiccant, which are corrosive and lead to corrosion of the mechanical components. This increases maintenance costs and decreases the cooling system’s lifespan. Herein, an encapsulation method is proposed to encompass the aqueous lithium bromide solution with silica as the shell, to protect the surrounding mechanical components. Moreover, a coating of citrate stabilized Au nanoparticles via an electroless method involving intermolecular electrostatic interactions is introduced to improve the robustness of the capsule wall. The success of the different coatings is evident from the change of zeta potential and mechanical properties. The coating with Au nanoparticles improves the mechanical strength of the capsules significantly, increasing rupture force from 0.25 ± 0.02 mN to 0.45 ± 0.04 mN. The coated and uncoated capsules were shown to be thermally stable over 10 repeated cycles between the temperature ranges −10 to 150 °C; hence, they withstand the thermal demands in ACs. Furthermore, adsorption and desorption cycles were performed on the capsules, which showed promising stable and repeatable performance.