Electrostatic Pressure and Line Tension in a Langmuir Monolayer

We present a Brewster angle microscopy study of the domains of liquid condensed phase (L₂) in the liquid expanded phase (L₁) in a Langmuir monolayer of a long-chain fatty acid. A strong deformation of the domains is observed when they are close to each other, indicating the presence of long-range repulsive dipolar interactions between them. The line tension of the L₁/L₂ interface is deduced from the balance between the line tension and the electrostatic forces. The latter were deduced from surface potential measurements.