Fabrication, morphology and thermal properties of octadecylamine-grafted graphene oxide-modified phase-change microcapsules for thermal energy storage

The demands for achieving microencapsulated phase-change materials (MEPCMs) with high thermal-energy storage ability have motivated increasing research interest in inorganic filler-modified MEPCMs. However, challenges for such MEPCMs still exist in the pursuit of good compatibility of inorganic particles with the core or shell material. Here, a novel type of octadecylamine-grafted graphene oxide (GO-ODA) -modified MEPCMs using melamine-formaldehyde (MF) resin as the shell material and the mixture of GO-ODA and n-octadecane as the core material was fabricated via in-situ polymerization. The alkylated GO with a thickness of similar to 1 nm was confirmed to be highly compatible with the core material. The as-prepared MEPCMs with a regular spherical shape were dispersed without any agglomeration, and the size decreased with increasing the filling amounts of GO-ODA. The incorporation of GO-ODA promoted the crystallization of n-octadecane, resulting in an observable reduction in supercooling degree. The encapsulation efficiency of MEPCMs was calculated to be over 88.0%, and the melting/freezing latent heats reached to a level as high as 207.2 J g(-1) and 202.5 J g(-1), respectively, even at a tiny loading level of 0.5%. Besides, the GO-ODA incorporated MEPCMs showed a good thermal cycling stability during a phase change. Moreover, a substantial enhancement in thermal transfer rate and a less marked heating effect for the MEPCMs containing GO-ODA were observed from the thermal conductivity tests and infrared thermography analysis. The findings suggested that the prepared MEPCMs are promising for applications in the fields of thermal energy storage and temperature regulation due to their enhanced thermal transfer performance and prominent phase-change enthalpy.