Formation and Structure of Coherent, Ultra-thin Calcium Carbonate Films below Monolayers of Stearic Acid at the Oil/Water Interface

Abstract

Detailed investigations of interfacial crystallization procedures are important to understand the basic principles of biomineralization processes. These interfacial phenomena can also be used to form new types of biomimetic composite materials. In a series of experiments we studied the influence of Langmuir-monolayers on the formation of ultra-thin calcium carbonate films. We systematically compared experiments performed at the water surface with results obtained at the water/oil interface. For stearic acid monolayers formed at the pure water surface, we were able to observe densely packed dispersions of ultra-thin CaCO₃ crystals, which were adsorbed below the surfactant membranes. We analyzed details of these structures by means of Brewster-angle-microscopy and other microscopic techniques. At the oil/water interface, however, we observed the formation of coherent, ultra-thin calcium carbonate films. These extended, two-dimensional crystalline structures were characterized by scanning electron microscopy, X-ray diffraction, and other techniques like interfacial-shear-rheology.