Electrowetting-based droplet volume modulation in T-junction microchannel

Droplet microfluidics has emerged as a transformative platform for high-throughput chemical, biological, and medical applications by enabling precise control over droplets of nanoliter-to-picoliter volumes. However, dynamic real-time modulation of individual droplet sizes within flowing arrays remains challenging due to inherent limitations in conventional pressure-driven systems. Here, we present an electrowetting-based strategy for on-demand droplet volume control in a T-junction microchannel. By leveraging voltage-induced electro-capillary forces at the tri-phase contact line, we achieve deterministic modulation of dispensed droplets. A scaling law derived from the Lippmann–Young equation quantifies the nonlinear relationship between droplet size and applied voltage, validated experimentally with direct current and pulsating supplies. Demonstrations show a threefold droplet volume adjustment and dynamic spatial encoding via pulsed voltages. Compared with existing droplet modulation approaches such as flow-rate control, surface acoustic waves, and thermal methods, our strategy provides broader tunability with lower system complexity and avoids material-specific constraints. Moreover, this study reveals a distinct fluid dynamic mechanism associated with wedge-shaped interface deformation. This approach combines high controllability with low system complexity, offering a versatile tool for real-time fluidic control in interdisciplinary research, thereby advancing lab-on-a-chip applications such as single-cell cultivation, combinatorial screening, and programable microreactors.