Long alkyl chain-grafted carbon nanotube-decorated binary-core phase-change microcapsules for heat energy storage: Synthesis and thermal properties

Microencapsulated phase-change materials (MPCMs) with carbon nanotube (CNT)-enhanced fillers and binary cores, which exhibit improved thermal conductivity and an adjustable working temperature range, are highly desirable for various heat energy storage applications. However, degraded properties are usually found for the CNT-enhanced MPCMs due to the poor compatibility of CNTs with PCMs, and the existing types of binary-core MPCMs (BCMPCMs) are quite limited. Herein, we prepared a novel type of BCMPCM with a n-octadecane/n-octacosane (C18/C28) mixture as the core, octadecyl isocyanate-grafted CNTs (OICNTs) as the enhancers and melamine-formaldehyde (MF) resin as the shell via in situ polymerization. Morphological and structural characterization of the OICNT-enhanced BCMPCMs demonstrated uniform distributions of OICNTs in both the core and shell. The determined phase-change temperatures were approximately 26 degrees C and 43 degrees C, with small degrees of supercooling. The phase-change enthalpy was as high as 187.9 J/g for a relatively large OICNT loading (3 wt %). Thermal conductivity measurements of the OICNT-enhanced BCMPCM/epoxy resin composites showed a 71.4% increase over that of the pure BCMPCM/epoxy resin composite. Moreover, the BCMPCMs experienced two separate temperature buffer stages resulting from the phase-change processes and exhibited a prominent thermal regulation capacity, which is of significance for their potential applications in the cooling of electronic devices, battery thermal management, utilization of waste heat, and air conditioning systems, etc.