Increasing the thermal conductivity of palmitic acid by the addition of carbon nanotubes

Four different methods, acid oxidation, mechanochemical reaction, ball milling, and grafting following acid oxidation, were used to treat multi-walled carbon nanotubes (MWCNTs). During treatment, hydroxyl groups, carboxylic groups, and amidocyanogen were introduced onto the surfaces of the MWCNTs. The MWCNTs were dispersed into palmitic acid (PA) to prepare phase change composites with high thermal conductivity. Both chemical treatment and ball milling help to break the MWCNT aggregates and to enhance their dispersibility. Measurements show that the thermal conductivity increase of the composites is highly dependent on the MWCNT pretreatment process. We propose that the difference in the interfacial thermal resistance between the MWCNTs and the matrix is due to the difference of the MWCNT surface state caused by different treatment processes. In all the MWCNT/PA composites, the one containing MWCNTs with hydroxyl groups, treated by a mechanochemical reaction, has the highest thermal conductivity increase, which, at room temperature, is up to 51.6% for a MWCNT addition of 1.0%.