Toward a predictive theory of wetting dynamics.

Area of Science:

• Physical Chemistry
• Materials Science
• Fluid Dynamics

Background:

• The molecular kinetic theory (MKT) of dynamic wetting relates contact angle deviations to energy dissipation at the contact line.
• Existing MKT models incorporate liquid viscosity and solid-liquid interactions but require empirical validation across diverse systems.

Purpose of the Study:

• To analyze a large dataset of dynamic wetting experiments to validate the molecular kinetic theory (MKT).
• To investigate the relationship between contact-line friction, liquid viscosity, and solid-liquid interactions.

Main Methods:

• Compiled and analyzed dynamic wetting data from over 20 publications, spanning molecular dynamics simulations to macroscopic systems.
• Examined data across 9 orders of magnitude in viscosity and 11 orders of magnitude in contact-line friction.
• Correlated contact-line friction coefficient (ζ) with liquid viscosity (ηL) and work of adhesion (Wa(0)).

Main Results:

• Confirmed the predicted dependence of contact-line friction (ζ) on viscosity (ηL) and work of adhesion (Wa(0)).
• Observed a broadly linear relationship between ln(ζ/ηL) and Wa(0)/n, with 85% of data within a defined envelope.
• Identified reasons for data scatter and proposed a semi-empirical model for predicting ζ.

Conclusions:

• The molecular kinetic theory (MKT) provides a robust framework for understanding dynamic wetting phenomena.
• The strong agreement across a wide range of systems supports the MKT's assertion that microscopic contact angles depend on contact line velocity.
• The findings facilitate more accurate predictions of dynamic wetting behavior in various applications.