Influence of Internal Phase on Capillary Break-Up Dynamics and Fluid Filament Stabilization in CNC-Stabilized Emulsions and Foams

The capillary break-up of two-phase colloidal dispersions occurs in numerous natural and engineering systems, such as the secretion of nectar by flowers and inkjet printing. In this study, we investigate the effect of the internal phase, whether liquid (droplet) or gas (bubble), on the dynamics of capillary break-up and fluid filament stabilization. We utilize cellulose nanocrystal (CNC)-stabilized emulsions and foams as model systems representing colloidal dispersions with internal liquid and gas phases, respectively. Our results demonstrate that, in CNC-stabilized emulsions, the internal liquid phase significantly influences the pinch-off dynamics compared to single-phase liquids. Emulsions transition from a yield stress to a viscoelastic response as the CNC concentration increases. This transition is characterized by self-similar thinning behavior similar to Newtonian fluids, with the emulsion threads following an exponential decay during pinch-off. The elongational viscosity and relaxation time, derived from the exponential decay constant, are directly dependent on the CNC concentration, enabling precise control over droplet formation and stabilization. In contrast, CNC-stabilized foams exhibit higher resistance to capillary break-up, with the pinch-off exponent being ten times smaller than that of emulsions. The presence of gas as the internal phase, stabilized by CNCs, enhances the stability of the foam films, preventing rapid pinch-off and promoting filament stabilization.