Investigation of spontaneous transition from low-molecular-weight hydrogel into macroscopic crystals

Here we describe the investigation of the spontaneous transition of a low-molecular-weight hydrogel into macroscopic crystals. The gelator based on the meta-hydroxy pyridinium salt of 1,2,4,5-benzene tetracarboxylic acid at a molar ratio of 1:2 formed standard a hydrogel, which remained in the gel state for a period of time but transferred afterward into macroscopic crystals without any stimulus from the environment. The transition process was characterized by multiple techniques, including environmental scanning electron microscopy (ESEM), UV-vis spectroscopy, and X-ray diffraction measurements. The results indicated that the transition process progressed in two steps: (1) after forming the initial crystals, the surrounding gelator molecules assembled gradually to them, and (2) as the gelator concentration decreased, the aggregating fibers dissociated gradually into solution, therefore making more molecules assemble to the crystals.