Surface modification of microencapsulated phase change materials with nanostructures for enhancement of their thermal conductivity

Microencapsulated phase change materials (MEPCMs) possess great potential as thermal energy storage materials for heating and cooling applications in industries. However, one important disadvantage of many MEPCMs is their low thermal conductivity. To enhance the thermal conductivity of PCMs, additives with high thermal conductivity are usually added into PCMs. However, these additives might not be mixed uniformly with the PCMs. Herein we report the first use of a polyurethane acrylic lacquer and hardener (PALH) as an adhesive to allow the additives to be uniformly coated on the surface of the shell of MEPCMs. A vacuum filtration assisted drop-casting method was employed to coat nano additives such as nano graphite, copper nanowires, titanium carbide and multi-walled carbon nanotubes (MWCNT) on the shell of commercial MEPCM (MPCM 28D) using PALH. MWCNT was found to be the most effective in improving the thermal conductivity of the MEPCM, giving an 87% increase when just 5 wt% of MWCNT was added. Field Emission Scanning Electron Microscope (FESEM) images confirm the successful uniform coating of MWCNT on the shell of MPCM 28D, while Differential Scanning Calorimeter (DSC) thermograms show that the phase change properties of MPCM 28D remain largely similar to the pre-coated MPCM 28D. Furthermore, thermal cycling tests indicate that MWCNT do not significantly affect the energy storage and release performance of MPCM 28D. These results indicate that coating MEPCMs with MWCNT can be a simple and effective method to improve their overall thermal conductivity without sacrificing its performance.