ADSORPTION OF INORGANIC POLYANIONS ALONG A LANGMUIR FILM - A BREWSTER-ANGLE MICROSCOPIC STUDY

Interactions of large inorganic polyanions along a positively charged Langmuir film of dimethyldioctadecylammonium bromide were studied by B rewster angle microscopy (BAM). Because of their large size (>10 Angst rom) and high refractive index, their adsorption along the organic mon olayer induces an increase of the interface reflectivity and can be di rectly monitored by BAM. Furthermore, they strongly modify the morphol ogy of the film and a coexistence of three phases (gaseous, liquid exp anded, and liquid condensed) is easily obtained at a temperature close to 20 degrees C. Around this ''triple point'', nucleation of liquid-c ondensed domains is observed along the gaseous/liquid-expanded interfa ce, inducing unusual structures such as strings of liquid-expanded dom ains. Those experiments demonstrate that inorganic/organic Langmuir fi lms based on the semiamphiphilic ionic association could present a var iety of morphologies as rich as those of classical amphiphilic molecul es at the gas/water interface.