I recently synthesized several ChCl: xylitol-based NADES without water, which were immediately transferred to sealed glass vials until further use. Some of the NADES remained transparent in the vials during storage. However, if the cap was removed, some of the NADES crystallized rapidly. Is there any explanation for this phenomenon? I understand that cooling may lead to the crystallization of NADES owing to less kinetic hindrance to crystallization. But why is a hermetic environment so essential to the stability of these NADES?