Preparation and properties of oleic acid decorated Cu₂O microcrystals/paraffin wax composites for phase-change actuation

Oleic acid (OA) decorated Cu₂O microcrystals/paraffin wax (Cu₂O-OA/PW) composites were synthesized by thermal decomposition of Cu (Ⅱ) formate-octylamine complexes in the PW using OA as a dispersing agent. The phase structure, morphology, chemical state and phase transition behavior were investigated by means of XRD, SEM, TEM, FTIR and DSC. The thermal sensitivity, thermal expansion and thermal stability of composites were also investigated. The results show that rhombic dodecahedron and cubic Cu₂O microcrystals are synthesized by changing OA concentration and precursor concentration. OA molecules are adsorbed on Cu₂O microcrystals by chemisorption way. The latent heats of Cu₂O-OA/PW composites shift to lower values compared to those of pure PW; however, the melting and freezing temperatures are kept almost the same as pure PW. With the increase of precursor concentration, the thermosensitivity of Cu₂O-OA/PW composites increases significantly, but the volume expansibility of composites decreases. There is no sediment in Cu₂O-OA/PW composites after being heated for many times, reflecting its excellent thermal stability.