Enhanced water evaporation via coupled capillary transport and gelation in confined nanocrystal systems

Drying in confined systems is a critical process with broad implications, spanning applications from materials science to water management in microscale technologies. Nevertheless, the coupled dynamics of transport and gelation in confined drying of colloidal suspensions remains poorly understood. Here cellulose nanocrystals (CNCs) are employed as a model system to systematically investigate the temporal dynamics, kinetic behavior, and structural transformation of nanocrystal suspensions during capillary drying. We report a mechanism whereby CNC suspensions, upon exceeding a critical concentration (∼1 wt%), undergo a transition from a fluid-like state to a kinetically arrested gel state at the evaporation front. This transition is accompanied by pinning of the evaporation interface at the capillary opening and leads to the formation of a gel-film heterostructure, consisting of a CNC gel layer with a water concentration gradient and a thin surface film formed via interfacial slip. This heterostructure promotes directional water transport from the capillary interior to the interface and significantly enhances the effective evaporative area, thereby accelerating the overall drying process. These findings offer insights into confinement-driven drying behavior and establish a framework for regulating evaporation kinetics in colloidal systems.