Rhythmic melting and crystallizing of ionic liquid 1-butyl-3-methylimidazolium bromide

We measured heat flow processes near the melting point of a typical ionic liquid, 1-butyl-3-methylimidazolium bromide ([C4mim]Br), using a laboratory-made differential scanning calorimeter with the base line stability of ±3 nW. We discovered the rhythmical exothermic and endothermic processes with the time scale of 101 s in the pre-melting region and in the region just after melting. This novel phenomenon is attributed to the link of the melting/crystallizing in domains and cooperative conformational change of the [C4mim]+ ion. It is also confirmed that about 1012–1013 ion pairs of [C4mim]Br are involved in the domains.