Characterization of Barrier Clay Coatings Using AFM and SEM, 2000 Coating Conference Proceedings

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M. Vaha-Nissi, J. Rintanen, J. Lahti, A. Savolainen, K. Rissa, T. Lepisto

A representative impression of the structure of the pigment coatings can be gained when both atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used for the characterization. AFM has turned out to be a powerful method for surface studies at ambient conditions. New imaging techniques have made it possible to characterize surface properties, in addition to the topographical features. Also scanning electron microscopy is a good method for structure studies of the coatings. For example determination of binder distribution and morphology of cross-sections can be done fairly easy by SEM. In the present study atomic force microscopy was used to e.g. characterize the coalescence of water based barrier coatings. The strong effect of drying conditions on the surface topography of the poly(styrene-butadiene) based dis-persion was observed. The effect of clay addition to the latex was evaluated by topographic images and in some cases also by using phase shift signal acquired in non-contact mode. In addition, barrier properties were evaluated. The structure of clay coating was examined by SEM using cross-sectional specimens. Large cross-sections of the coatings were prepared by metallographic-like sample preparation technique. Backscattered electron (BSE) imaging revealed clear contrast between the binder and the pigments when osmium tetroxide was used for staining of poly(styrene-butadiene) based binder. Binder distribution and coating morphology of pigment coatings were evaluated from the images.