Effect of Anions on the Memory Effect in the Tetra-n-butylammonium Dicarboxylate Semiclathrate Hydrate Reformation

Semiclathrate hydrates (SCHs) have been expected to be one of the phase change materials for cold energy storage. The large degree of supercooling in SCH formation, however, is a major obstacle to the practical applications of SCHs. As a way to suppress the degree of supercooling, we focused on the memory effect (a kind of temperature hysteresis) in the tetra-n-butylammonium dicarboxylate SCHs. The tartarate, malate, and succinate anions, which have similar chemical structures, were used as anions. As a result, the ability to retain the memory effect in the TBA-tartarate SCH was the largest of the three SCHs. The interaction of the substituted hydroxy group(s) of anions with surrounding water molecules in the aqueous solution might improve the thermal stability of the solution structure that causes the memory effect, resulting in promotion of the SCH reformation.