Dynamic Wetting and Spreading of High-Viscosity Liquids on Grooved Substrates

Liquid filament formation and spreading on grooved substrates play a crucial role in applications ranging from microfluidics to material deposition. Despite extensive studies on capillary-driven spreading, the dynamics of liquid filaments, particularly for high-viscosity, high-surface-tension liquids, remain poorly understood. Here, we investigate the wetting and spreading behavior of glycerol-water mixtures on structured surfaces with varying groove widths (8 µm to 32 µm) and depths (15 µm). Using a combination of experiments, finite element simulations, and theoretical analysis, we reveal the interplay between capillary forces, viscous resistance, and gravity in governing liquid filament propagation. The results demonstrate a consistent t4/5 scaling law for filament length over time, reflecting the balance of capillarity and gravity in the long-time regime. Narrower grooves enhance capillary confinement, promoting faster and more uniform filament spreading, while higher viscosity slows propagation. Finite element simulations confirm these findings, reproducing experimental trends and elucidating the role of groove geometry on filament dynamics. Theoretical analysis based on the lubrication equation provides a robust framework for understanding these behaviors. Our findings advance the understanding of liquid filament dynamics on structured surfaces and offer insights for optimizing grooved substrates in microfluidic, sensing, and material processing applications.