A series of nanocomposite phase change materials (PCMs) were prepared by dispersing sodium dodecyl sulfate (SDS) functionalized multiwall carbon nanotubes (MWCNTs) in liquid polyethylene glycol 8000 (PEG8000) with various mass fraction loadings (0, 0.5, 1, 2, and 5%). The effects of functionalized MWCNTs on form-stability, and thermal behaviors, such as latent heat, thermal stability, thermal reliability, thermal conductivity, and thermal storage/release rate, of PEG8000 were investigated experimentally. The results showed that the melting peak temperatures and latent heat of melting of the nanocomposite PCMs decreased slightly from 63.9 to 61.9 degrees C and 165 to 150J/g when the mass fraction of functionalized MWCNTs increased from 0 to 5% gradually. The nanocomposite PCM showed excellent form-stability with 2% MWCNTs loading even when the temperature was about 36 degrees C (100 degrees C) higher than the melting peak temperature of pure PEG8000 (63.9 degrees C). In addition, the thermal conductivities of nanocomposite PCMs were increased from 0.295 to 0.531W m(-1) K-1 progressively by adding 0.5 wt% to 5 wt% MWCNTs, respectively. Moreover, the thermal performance tests indicated that the thermal storage and release rates of the as-prepared nanocomposite PCMs increased due to the addition of small amount of MWCNTs. The PEG8000/MWCNTs nanocomposite PCMs showed a proper thermal behavior for thermal energy storage applications. (C) 2019 Elsevier Ltd. All rights reserved.