The anomalous behaviour of aliphatic fatty diamides: Chain length and hydrogen bonding interactions

A series of five linear aliphatic diamides were synthesised via facile direct coupling of stearic acid (C18) with diamines of varying carbon number (18-n-18, n = 2, 4, 6, 8 and 10) in a catalyst-free neat reaction. The compounds were investigated as potential renewable phase change materials (PCMs) for latent heat thermal energy storage. The thermal properties of the diamides were predictably related to the diamine chain length. TGA measurements indicated that the diamides evaporated before decomposition, with evaporation onsets increasing from 325 °C for 18-2-18 to plateau at 337 °C for the longer-chain diamides. The diamides display negligible supercooling and melt and crystallize at 140 °C–150 °C within a narrow transition span ( 100 °C.•High phase transition temperatures (~150 °C) and thermal storage density (~220 J/g).•Hydrogen bonding of the amide groups influenced by diamine chain length.•Melting and crystallization affected primarily by hydrogen bonding of amide groups.•Latent heat primarily dependent on dispersive forces of the fatty acid moieties.