Preparation Of Phase Change Material: Functionlized Carbon Nanotubes/Palmitic Acid Composite

Carbon nanotubes (CNTs) have extraordinary mechanical and thermalproperties and have the potential for a wide variety of applications.Composites with CNTs as additives can enhance the thermal properties of thematrix materials. Because MWNTs as produced are usually entangled and notready to be dispersed into organic matrix, efforts had been taken to developdispersion and functionalization techniques. To employ MWNTs as effectivethermal conductive additives in polymer nano-composites, proper dispersionand appropriate interfacial adhesion between the MWNTs and polymer matrixhave to be guaranteed. In this work, MWNTs were treated by mixed acidoxidation and pyrogallol adsorption,oxidized groups have been introduced onthe surface of MWNTs. Treated MWNTs were dispersed into the palmitic acidmatrix. Stable and homogeneous MWNTs and palmitic acids (PA) compositeswere successfully prepared.Differential scanning calorimeter (DSC) was used to measure the phasechange temperature, phase change latent heat and thermal storage time ofthese nanotube composites. Experimental results show that, compared with pure palmitic acid, the phase change latent heat of the composite decreaseswith the increase of MWNTs content. For a given mass fraction of MWNTs inthe composite, the phase change latent heat increases with the oxidation timeof the MWNTs. For mass fraction of MWNTs of1wt%, and the oxidationtime of MWNTs of10hours, the phase change latent heat decreases1.62%,and the thermal storage time decreases8.4%. For the oxidized MWNTsadsorbing with pyrogallol, the thermal storage time decreases16.3%.After100thermal cycles, the phase change temperature, latent heat andchemical structure of the MWNTs/PA do not show observable change,indicating that the nanocomposite materials have good thermal reliability.In order to further investigate the factors that influence the dispersibilityof MWNTs, X-ray photoelectron spectroscopy (XPS) was used to analysis thebasic elements of MWNTs. The results indicate that the increase of carbonylcontent on MWNTs by increasing oxidation time and adsorbtion of pyrogalloyis responsble for the good dispersion ability of MWNTs in PA.