Controlling microfluidic droplet splitting in T-junction via wall slip

Precise control over microdroplets is vital in various microfluidic applications like drug delivery and cancer cell separation, among others. At micro/nanoscale dimensions, the conventional no-slip wall boundary condition becomes unreliable, giving rise to slip velocity at channel walls. This study investigates the influence of wall slip on droplet splitting dynamics in a microfluidic T-junction using a conservative two-phase level set method implemented in COMSOL Multiphysics® (version 5.3). The slip length (β) has been varied from 0.1 to 3μm, with capillary numbers (Ca) ranging from 0.0071 to 0.0338, while fluid properties were kept constant to isolate the effect of wall slip on droplet dynamics. The splitting process has been categorized into three stages: entering, squeezing, and post-splitting. Increasing the slip length leads to a flatter velocity profile, reduced shear-induced resistance, and altered pressure gradients, all of which influence droplet deformation and splitting. At smaller slip lengths, enhanced fluid–solid interactions lead the droplet tip to advance farther into the daughter channel before undergoing splitting. Results also reveal that higher slip lengths and capillary numbers accelerate neck thinning and shorten splitting time. As the slip length increases and the capillary number decreases, the neck center of the droplet interface shifts closer to the junction inlet. Finally, flow map diagrams with power-law correlations identify distinct flow regimes, including no splitting, splitting with tunnel, and splitting with obstruction, with regime boundaries shifting toward higher droplet lengths as slip length increases at a fixed capillary number. This work provides key insights into the interplay between slip length and droplet dynamics, offering a pathway for optimizing microfluidic platforms in biomedical and lab-on-a-chip technologies.