Supercooling suppression of microencapsulated phase change materials by optimizing shell composition and structure

•A new method for supercooling suppression of microPCMs by optimizing the structure of the microcapsule shell.•Large effective latent heat (up to 213J/g) of the microPCMs, much higher than those using additive as nucleating agents.•Change of shell composition and structure significantly affects the phase transition processes of the encapsulated PCMs.•The latent heat of the shell-induced phase transition is maximized, reaching 83.7% of the latent heat of bulk octadecane.•Hollow spheres with porous rather than solid resin shell are also formed when the SDS concentration is very high. A new method for supercooling suppression of microencapsulated phase change materials (PCMs) has been developed by optimizing the composition and structure of the microcapsule resin shell. The microcapsules comprising paraffin octadecane encapsulated in melamine–formaldehyde resin shell were synthesized with the use the oil-in-water emulsion technique. These PCM microcapsules are 5–15μm in diameter. The supercooling of these octadecane microcapsules can be as large as 13.6°C, when the homogeneous nucleation is dominant during the melt crystallization into the thermodynamically stable triclinic phase. It is discovered that the homogeneous nucleation can be mediated by shell-induced nucleation of the triclinic phase and the metastable rotator phase when the shell composition and structure are optimized, without need of any nucleating additives. The effects of synthesis parameters, such as ratio of melamine to formaldehyde, pH of pre-polymer, and pH of emulsion, on the phase transition properties of the octadecane microcapsules have been investigated systemically. The optimum synthesis conditions have been identified in terms of minimizing the supercooling while maintaining heat capacity. Potential applications of this type of phase changeable microcapsules include high heat capacity thermal fluids, thermal management in smart buildings, and smart textiles.