Influence of internal phase transition on the pinch-off dynamics of emulsion threads

Pinch-off dynamics are important in processes like 3D printing and coating. For emulsion droplets, where the continuous phase contains dispersed immiscible sub-droplets, these dynamics are not well understood. We study the pinch-off dynamics of concentrated emulsions (75% dispersed phase) undergoing time-dependent sol-gel transitions. High-speed imaging and rheology are used to examine water and sol-gel droplets in oil stabilized by Span 80. We study emulsions at two aging times: 10 minutes (liquid dispersed phase) and 90 minutes (gelled phase). Results reveal a significant increase in both viscosity and elastic moduli as gelation progresses. The shift in rheological properties significantly alters pinch-off behavior. Water emulsions and early-stage gel emulsions form short filaments and thin rapidly, with a power-law thinning dynamics, t^α, where α ≈ 2/3 and α ≈ 1, respectively, signalling inertial and viscous pinch-off regimes. In contrast, aged gel emulsions develop long, stable filaments with slowed thinning and reduced scaling exponent. The internal-phase transition significantly alters filament breakup dynamics in emulsions, offering a route to control droplet detachment, with direct implications in printing, encapsulation, and soft material processing.