Textures and phase transitions in Langmuir monolayers of fatty acids. A comparative Brewster angle microscope and polarized fluorescence microscope study

Abstract

Brewster angle microscopy (BAM) and polarized fluorescence microscopy (PFM) are used to observe the distinctive textures of and the transitions between condensed phases in Langmuir monolayers of n-alkanoic acids. BAM is sensitive to film anisotropy even when the molecules are not tilted as long as the unit cell is anisotropic. Every transition is visible with one or both of the techniques, either as a dramatic change in the degree of contrast or as a sudden alteration of the mosaic domain texture. The two techniques are generally consistent, although the presence of the fluorescent probe impurity (for PFM) causes a subtle difference in the appearance of one transition and small shifts in transition surface pressures.