Molecular Aggregation Structure of Barium Stearate Monolayer Based on Electron Microscopy

Aggregation structure of barium stearate monolayers prepared from a benzene solution at various surface pressures was investigated by using a transmission electron microscope. Two-dimensional crystallites of the monolayer were formed even at the surface pressure of 0 mN · m−1. The monolayer crystallites on the water surface became a continuous phase at 25 mN · m−1 and collapsed at 40 mN · m−1. The surface pressure–area isotherm represents an aggregating process of the small two-dimensional crystallites on the water surface, instead of a generally accepted concept on phase transitions among gas, liquid, and solid phases.