TURBIDITY STUDY OF THE PROCESS OF FILM FORMATION OF THIN-FILMS OF AQUEOUS ACRYLIC DISPERSIONS

This study was directed towards determining the factors that define the process of film formation of binder particles in drying aqueous dispersion coatings, based on acrylic polymers. The work described focuses on the intrastructure of drying and ageing thin films of acrylic latices. In concentrated latices the binder particles are arranged in closely packed structures which cause colored light patterns, the so-called Bragg diffractions. The light waves move within the latex film, where the waves are scattered by the internal structure composed of the spheres and water voids. The pattern of light transmission reveals the internal structure of the latex film. From the change in interference during the drying process of a thin latex film, it is possible to follow the internal movement and deformation of polymer spheres (coalescence process). Further coalescence results in a transparent film. When this film is immersed in water, the remaining internal interfaces between the adhered binder particles swell, thus regenerating the interference pattern. It is expected that during ageing of the film, the proportion of internal interfaces will decrease with time, so that when the aged film is immersed in water the remaining internal interfaces will swell. The resulting interference pattern reveals the decrease in the interfaces between the deformed polymer particles in the dried latex film (auto-adhesion process).