Bidirectional strain release in a thermosalient organic salt crystal induced by anisotropic thermal expansion and phase transformation

Abstract

The jumping of crystals in the presence of external stimuli such as temperature, light, and mechanical forces is observed due to the release of accumulated strain in the crystal. Thermosalience in molecular crystals is generally induced by anisotropic thermal expansion accompanied by phase transformation. However, a thermosalient effect has not been observed in the same crystal at two different temperature zones caused by two distinct mechanisms. Here, we report the bidirectional release of strain leading to jumping by heating and cooling of an organic salt crystal of SQIM. Jumping of the crystals by heating is driven by anisotropic thermal expansion coupled with a change in hydrogen bonding and contraction of the imidazolium cation, whereas jumping of crystals by cooling is attributed to the contraction of inter-layer distance followed by shear-induced phase transformation.