ATOMIC-FORCE MICROSCOPY STUDY OF POLYSTYRENE LATEX FILM MORPHOLOGY - EFFECTS OF AGING AND ANNEALING

The surface topography of polystyrene latex thin films (similar to 1-mu m thick) deposited from surfactant-free latex dispersions onto mica was investigated by atomic force microscopy (AFM) as a function of particle size, annealing time and temperature, and aging at ambient temperatures. The films were observed to be polycrystalline, consisting of hexagonal domains of long-range, close-packed particles. Greater particle monodispersity resulted in fewer crystal defects. Films aged at ambient temperatures did not exhibit interparticle fusion, within the resolution Limits of the AFM. Limited particle fusion is observed when the films are annealed: the particle heights decreased dramatically but only when heated at temperatures above the glass transition of polystyrene, whereas the interparticle distance between adjacent, close-packed particles was observed to remain constant under all annealing and aging conditions. A smaller particle sized latex resulted in a faster rate of interparticle fusion, thought to be due to a greater capillary force between the smaller particles. Crystal defects at the film surface became larger in size as a result of annealing, but there was no measurable increase in the number of defects.