Spherical polymer containers with a fluid polymer core: Synthesis and characterization of film formation by AFM

Two-stage emulsion polymerization controlled with a reaction calorimeter re sults in core-shell structured latexes with homogeneous size distribution a nd architecture. We describe the synthesis of so-called "container particle s", consisting of a low-viscosity core with a low glass transition temperat ure (poly(2-ethylhexyl methacrylate), (PEtHMA)), covered with a thin shell of a cross-linked rubber (poly(n-butyl acrylate), (PBA)). Drying of these d ispersions results in nanostructured films. A controlled topography and a n etwork superstructure are obtained, which may be adjusted by the size, comp osition, and architecture of the original particles. Atomic force microscop y (AFM) in the tapping mode is used to study the final latex films. In addi tion to topographic information, it is possible to display, with a nanomete r resolution, the amplitude and phase of response of the cantilever in each pixel, which images the remainder of the former core and shell by their di fferent mechanical loss behavior. The degree of cross-linking of the second stage polymer (PBA) is found to be the major factor influencing the morpho logy of the polymer films formed. At lower cross-linking densities, even an d surface mechanically homogeneous films are obtained. For highly crosslink ed shells, it is shown by a combination of AFM modes that the containers co llapse and release the low molecular weight liquid core to form a continuou s film containing the single, collapsed units.