Capillary Rise: Validity of the Dynamic Contact Angle Models

Area of Science:

• Fluid Dynamics
• Surface Science
• Physical Chemistry

Background:

• The classical Lucas-Washburn-Rideal (LWR) equation often overpredicts capillary rise compared to experimental results.
• This discrepancy is largely attributed to the influence of velocity-dependent dynamic contact angles, not accounted for in the equilibrium model.

Purpose of the Study:

• To investigate and compare various dynamic contact angle models for their effectiveness in correcting capillary rise predictions.
• To analyze the role of molecular-level phenomena in dynamic contact angle effects during capillary rise.

Main Methods:

• Conducted capillary rise experiments using diverse wetting liquids in borosilicate glass capillaries.
• Compared experimental data with predictions from LWR equations modified by different dynamic contact angle models (molecular kinetic theory, hydrodynamic, Joos' empirical, molecular self-layering).

Main Results:

• LWR equations modified by molecular kinetic theory and hydrodynamic models showed good predictions with fitting parameters for all tested liquids.
• The molecular self-layering model provided accurate predictions for specific liquids (carbon tetrachloride, octamethylcyclotetrasiloxane, n-alkanes) and silicone oils across a range of viscosities.
• The molecular self-layering model highlighted the significance of the pre-meniscus wetting film in energy dissipation.

Conclusions:

• The molecular self-layering model offers superior accuracy in predicting capillary rise, emphasizing the importance of molecular film dynamics.
• This model provides valuable insights into the capillary dynamics of polymer melts and other complex fluids.