Thermodynamics of crystal formation and growth in a sessile droplet

Accurately detecting subtle thermodynamics during crystallization and associated water evaporation processes, especially around seed formation, has been challenging. Here, we report a method to investigate the complex energy changes during these simultaneous endothermic and exothermic events. We employ an open-space microcalorimeter, coupled with optical observation using a microscope equipped with a camera for real-time monitoring. This method reveals crystal formation by observing energy changes and simultaneously visualizing the sample. The concentration influence for potassium chloride crystallization is analyzed, including energy released and the evaporation thermodynamics using isothermal microcalorimetry. We also monitor the energy dissipation during crystallization, showing an ≈4.2 s period for potassium chloride crystal seed formation with a released energy of ≈11.9 μJ. This method can potentially reshape strategies for controlled crystallization across diverse industrial and laboratory settings. Extending beyond potassium chloride, our findings shed light on broader crystallization dynamics, paving the way for innovations in materials and energy sciences.