In situ monitoring of drying complex droplets on superhydrophobic surface: from gelation to crystallization

Abstract Understanding the evaporation dynamics of droplets of nanoparticle (NP) suspensions is crucial for applications in coatings, printing, and colloidal assembly. In this study, we employ laser speckle analysis (LSA) combined with controlled substrate vibration to investigate the collective dynamics and crystallization of NPs during droplet evaporation on superhydrophobic surfaces. LSA allows us to characterize the evolution of NP spatial and temporal collective behavior throughout the drying process, capturing multiple transition stages, including gelation and capillary-driven crystallization. Meanwhile, controlled vibration acts as a tunable external force that modulates particle interactions, influencing particulate patterns and leading to more uniform NP deposits. Our results demonstrate that substrate vibration significantly affects the structural evolution of NP assemblies, offering new insights into the fundamental mechanisms governing NP organization in confined geometries.