Multifunctional composite phase change material with electrostatic self-assembly structure based on carboxylated multi-walled carbon nanotubes

The need for improved thermal regulation in electronic devices and solar thermal energy storage, prompted by the energy crisis, has expedited the advancement of phase change materials (PCMs). Carboxylated multi-walled carbon nanotubes (MWCNT-COOH) were produced by introducing carboxyl functional groups onto MWCNTs utilizing a concentrated acid treatment. The novel composite was engineered through an electrostatic self-assembly process between the negatively charged MWCNT-COOH and the positively charged Poly dimethyl diallyl ammonium chloride (PDDA) solution, filling the structure with the PCM polyethylene glycol (PEG) and incorporating the (magnesium hydrate) Mg(OH)₂ to enhance the material's flame resistance at high temperatures. The thermal conductivity of the obtained composites improved significantly from 0.25 W/m·K to 1.183 W/m·K, while maintaining an enthalpy of phase transition of phase change of 135.1 J/g. Owing to the capillary effect of the closely packed MWCNT-COOH tubular structure, the composite material exhibited excellent high-temperature shape retention ability. Additionally, the composite demonstrated high absorption with an absorbance reaching 1.18 L/(g·cm) and composite materials can convert up to 86.8 % of light energy into heat energy.