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Aliphatic diamides derived from vegetable oils have been shown to significantly extend both the phase transition temperatures and melting enthalpy of phase change materials (PCMs) for thermal energy storage (TES) applications. Relationships between molecular structure and thermal functionality of aliphatic fatty diamides were established in this work through the study of twelve (12) synthesized symmetrical aliphatic diamides CH3(CH2)m-2CONH(CH2)nHNOC(CH2)m-2CH3 of series m-n-m (fatty acids chain length, m = 12, 14, or 16 and diamine, n = 2, 4, 8 and 10). This study extended the understanding derived from previous studies of nine (9) other aliphatic diamide molecules. The diamides were assessed in terms of crystal structure, thermal stability, thermal transition behavior and possible kinetic effects using XRD, TGA and DSC. This facilitated an investigation of the role structural factors play in phase change characteristics: (1) the aliphatic chain, which facilitates orientation, (2) the balance between the amide interaction through hydrogen bonding and the intra amide steric repulsions and (3) the molecular conformation which drive the entropy of phase change. The study clarified the nature of the competition between dispersion forces, hydrogen bonding, entropic and mass effects in aliphatic fatty diamide PCMs and established molecular structure – thermal function correlations which can assist in intelligent design of superior aliphatic fatty amide molecules for TES applications. |
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