Hydrodynamic analysis of the advancing dynamic contact angle in microtube

We explored the hydrodynamic features of dynamic wetting both theoretically and experimentally. We studied the triple-line motions of glycerol-water solutions of various viscosities (85-456 mPa·s) in microglass tubes (300, 500 and 1000 μm in diameter). First, dynamic (advancing) contact angles were measured and compared with those of a well-known hydrodynamic model (O.V. Voinov, Hydrodynamics of Wetting, Fluid Dynamics (1976)). Second, the internal flow structures near moving menisci were visualized using micro-particle image velocimetry (μ-PIV). Several differences in flow shape (compared to those predicted by theory) were observed. Ultimately, we present a new method by which dynamic contact angles may be predicted, derived from analysis of wall shearing stress at the moving contact line to reflect on the liquid-solid interaction effect. Our analysis has the advantage of incorporating the effect of contact angle hysteresis on the dynamic contact angle. The modified approach yielded data in good agreement with our experimental results and other open-literature data. We thus fundamentally explored the hydrodynamic aspects of dynamic wetting.