Dynamics of Three-Phase Moving Contact Lines

Dr. R.L. Cerro

Department of Chemical and Materials Engineering
University of Alabama in Huntsville

October 12, 2001

Abstract

Flow patterns near the moving contact line have a strong effect on heat and mass transfer in multiphase fluids and on the deposition of mono-molecular Langmuir-Blodgett ultra-thin films.

Despite the fact that during the last part of the XXth century many efforts were devoted to perform theoretical and experimental research on moving contact lines, the dynamics of moving contact lines is one of the outstanding problems of modern fluid mechanics.. Classical hydrodynamic solutions do not agree with experimental observations. Recent developments demonstrate that flow patterns near contact lines cannot be explained without the introduction of molecular and double layer forces at the three-phase region.

At low contact line speeds, inertial effects can be neglected and the hydrodynamics of moving contact lines are represented by streamline functions satisfying the bi-harmonic equation. Purely hydrodynamic boundary conditions cannot explain experimental data. To introduce the effect of molecular and double-layer forces on equations and boundary conditions, one must parcel the domain of flow into succesive regions where viscous forces are balanced by molecular, capillary, and gravity forces as one moves away from the contact line. The solutions to the bi-harmonic equation thus found, show excellent agreement with available experimental data and can be used to explain seemingly contradictory experimental findings.