The molecular-kinetic approach to wetting dynamics: Achievements and limitations

Area of Science:

• Physical Chemistry
• Surface Science
• Fluid Dynamics

Background:

• The molecular-kinetic theory (MKT) has been a cornerstone in understanding dynamic wetting for five decades.
• It elucidates the relationship between dynamic contact angles and meniscus speed by quantifying non-hydrodynamic dissipation.
• The MKT has been adapted for various fluid systems and incorporates bulk viscosity and surface diffusion effects.

Purpose of the Study:

• To critically review the achievements and limitations of the molecular-kinetic theory (MKT) in dynamic wetting.
• To highlight common misinterpretations and areas where the MKT's predictive power is compromised.
• To assess the reliability of molecular parameters derived from experimental data within the MKT framework.

Main Methods:

• Review of existing literature on the molecular-kinetic theory (MKT) of dynamic wetting.
• Analysis of the MKT's application to solid-liquid-vapor and solid-liquid-liquid systems.
• Evaluation of the MKT's predictions regarding contact angle dependence on speed, wetting/dewetting limits, and optimal coating conditions.

Main Results:

• The MKT successfully explains most qualitative aspects of dynamic wetting, including speed dependence and dissipation.
• It predicts optimal intermediate wettability for high-speed coating and defines maximum wetting/dewetting speeds.
• However, derived molecular parameters often exhibit significant scatter and lack reliability, limiting precise quantitative predictions.

Conclusions:

• The MKT remains a valuable, flexible tool for rationalizing dynamic wetting phenomena and fitting experimental data.
• Despite its successes, the inherent unreliability of its molecular parameters necessitates caution in quantitative applications.
• Further refinement or alternative theories may be needed to overcome the limitations in parameter accuracy for dynamic wetting.