Fluid front pinning in a microchannel under constant pressure

Abstract

Fluid transport at the microscale is fundamentally governed by interfacial phenomena, and geometric irregularities strongly influence flow behavior. Specifically, the sudden pinning of liquid fronts at channel roughness plays a crucial role in the design and operation of microfluidic systems. However, the kinematic dynamics of the interface during the pinning and detachment phases remain poorly understood under constant pressure conditions. In this work, we show that the sudden velocity increase after fluid detachment depends exclusively on the system’s geometry. Using optical microscopy to track an advancing meniscus over a controlled roughness, we demonstrate a universal geometric deformation independent of fluid viscosity or applied pressure. This geometric defect forces the interface to deform, leading to an accumulation of surface potential energy. Upon detachment, this energy is abruptly released, producing the observed kinematic acceleration