Formation of opaque films by biomimetic process

The preparation of opaque white films with amorphous aluminium polyphosphate, crystalline calcium carbonate and poly(vinyl acetate) latex is described. Film optical properties were characterized by diffuse reflectance spectrophotometry; morphological film features were examined by SEM, TEM, STM and AFM. Domain organization and void formation were detected, with dimensions of the same order of magnitude as the wavelength of visible light and can thus account for the film optical properties. Calcium carbonate consumption was monitored by X-ray diffraction and is assigned to a chemical reaction with aluminium polyphosphate, in which a mixed Al-Ca carbonate-polyphosphate is formed. The process of film opacification is interpreted as a result of dispersion, chemical reaction and orientation of solid inorganic particles within the polymer network during the film drying process. A model is proposed for void formation, based on volume contraction of the swollen inorganic particles, at a stage when their rigid surfaces are bound to the polymeric matrix. This revised version was published online in November 2006 with corrections to the Cover Date.