Enhanced temperature-responsive functions of thermal metamaterials by interface engineering

A phase-change thermal metamaterial (PCTM) has attracted a lot of attention to implement responsive thermal functions that can be adaptable to ambient environments. Temperature responsive PCTMs consisting of aligned metal backbones and phase change materials (PCMs) are capable of transforming artificial heat paths enabled by rapidly transiting thermophysical characteristics at certain temperatures. However, fabricating the PCTMs essentially involves the interfacial boundaries of different materials such as metal and PCMs, thereby degrading thermal transport between them. Moreover, while the phase of the material is altered from solid to liquid or vice versa, the instability of the interfaces inevitably occurs. Herein, we report an interface engineering of PCTMs using layer-by-layer (LbL) coating layers and nanocomposite PCMs to improve the on/off switching transition of thermal functions manipulating the heat flux in response to a specific temperature. LbL-assembled ultra-thin interfaces (multi-walled carbon nanotube (MWCNT)-polyethylenimine (PEI) layers and MWCNT-PEI-Silane layers) as interfacial thermal resistance compensators and PCM nanocomposites using graphene nanoplatelets (GNPs) are incorporated into thermal shifters based on stainless steel backbones. The LbL interfaces reduce the physical voids and phonon scattering between PCMs and metal surfaces while the GNP fillers increase the thermal conductivity of the PCMs in solid phases. The engineered PCTMs highly amplify the on/off switching ratio of thermal shifter unit cells and enhance overall thermal functions of temperature responsive TM modules (shield, concentrator, diffuser, and inverter). This work can pave a way for feasible solutions of interfacial resistances and instability in TMs.