LATEX FILM FORMATION STUDIED WITH THE ATOMIC-FORCE MICROSCOPE - INFLUENCE OF AGING AND ANNEALING

The surface structure of latex dispersion films was examined with an a tomic force microscope. All measurements were done in air on latex fil ms having a minimum film formation temperature of 12 degrees C and a g lass transition temperature of 18 degrees C. One aim of this study was to follow structural changes during film formation. Three minutes aft er spreading the film, its surface layer dried. Afterwards, the struct ure of the film did not change anymore. Only after 4 months could stru ctural changes be observed: Though individual latex particles could be identified, the particles partly melted into one another. After annea ling films at 50 degrees or 60 degrees C for 4 h, the latex particles partly melted into one another, but individual particles could still b e identified. When annealing at or above 80 degrees C, no individual l atex particles were visible anymore. With increasing temperature the f ilm roughness decreased from 3 nm without annealing to 0.8 nm at 100 d egrees C annealing temperature. In addition, islands of 2-4 nm thickne ss appeared on the film surface. These islands could be scraped off th e film by increasing the force between tip and sample, indicating that they are composed of surfactant which was squeezed out of the film.