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Phase Change Heat Insulation Based on Wax‐Clay Nanotube Composites

Wax can be used as a phase change material in solar energy storage but has low thermal conductivity and cannot sustain shape at higher temperature (above 55 °C). Introducing 50% halloysite clay nanotubes into wax yields a stable and homogenous phase change composite with thermal conductivity of 0.36 Wm–1 K–1 and no leaking until 70 °C. Graphite and carbon nanotubes can further increase the conductivity and shape stabilized temperature as high as 1.4 Wm−1 K−1 and 91°C. Vectorial thermal energy transfer for double layers of different composition was demonstrated: heat flux difference in the opposite directions differed by 25%. The new wax‐nanoclay composite is a promising heat storage material due to good heat capacity, high thermal conductivity and ability to preserve its shape during wax melting.