Morphology of heterogeneous latex particles investigated by atomic force microscopy

Abstract

To investigate the morphology of individual latex particles with the atomic force microscope the particles were adsorbed onto mica and then dried. During adsorption and subsequent drying the packing of the particles is probably mainly determined by capillary forces, their deformation is caused by van der Waals forces. The shape of the particles on the mica surface depends on their original morphology and their viscoelastic properties. Chemically and also morphologically heterogeneous latex particles with therefore different viscoelastic properties were examined in comparison to the corresponding homogeneous latexes.

In addition, films formed with the latex particles were imaged to correlate the structure of individual particles with that of the film surface.

With the AFM it is possible to examine the morphology, size and viscoelastic inhomogenities of latex particles and thereby deduce their behavior during film formation. The particles examined here were on the monomer basis of n-butylacrylate and methylmethacrylate.

To compare the morphology of single particles with the surface structure of the corresponding films, we have chosen two different heterogeneous particles: For sample COM 1, we assumed a core-shell morphology, for sample COM 2 a hemispherical particle form. The morphology assumptions were based on studies which compare the minimum film formation temperatures with the glass transition temperatures of the different particle phases and their mass fractions. The results observed by the heterogeneous particles were compared to the corresponding homogeneous ones. Both composite particles exhibit the speculated morphology and, consequently, the expected properties after film formation.