General behavior and mechanisms of dendritic crystal formation in evaporated biological solutions and their significance for solution analysis

Abstract

By studying the evaporated crystallization of 1640 solutions and some protein + salt solutions, we revealed for the first time the onset and dynamic process, the behavior, and general rules of the dendritic crystal growth as a function of temperature, pH value, and the concentrations of their major components (NaCl, KCl, NaHCO₃, and d-glucose). We proposed the crystallization mechanism for each of them at various conditions and indicated the factors that control the formation of dendritic crystals. We showed that at a temperature ranging from 20 to 40 °C, only the solution mixed with crystalline and amorphous substances could form dendritic crystals. The rise in temperature and decreasing pH from the neutral value would reduce the pattern divergence induced by different components and concentrations. Increasing the content of the crystalline substances would make the dendritic crystals thicker and have less branching. The dendritic crystals are mainly composed of the salt with the highest ratio R of concentration/solubility. The crystal structure of the salt also determines the shape of the dendrites. The amorphous substances mainly distribute at the edge of the dried spot to form a ring and deposit in the gaps between the dendritic crystals or the growing tips of the dendrites. This study suggests that based on the behavior of the dendrite growth, it is possible to use the methods of dendrite formation and pattern analysis to replace analytical instruments for some solution physicochemical tests or grow dendritic crystals with desired patterns for various applications.