Characterization of Particle Coalescence in Waterborne Coatings Using Atomic Force Microscopy

By R.M. Rynders, C.R. Hegedus, A.G. Gilicinski

Atomic force microscopy (AFM) was used to image coatings formed from blends containing various ratios of three waterborne acrylic/polyurethane hybrid polymers. Tapping and contact mode AFM were evaluated for this application, and tapping mode proved to be the best method due to the low friction forces.

It was shown that when the tip and feature sizes were similar, the superposition of the tip morphology on the surface features in the AFM image was significant. AFM imaging of gold colloids dispersed on mica and scanning electron microscopy of the tip were used to characterize the AFM tips.

A method was developed to estimate the tip radii; inturn, the tip size was accounted for in analyzing the dimensions of the coating surface features. The degree of particle coalescence was evaluated from the AFM images. The polymer blends were ranked according to the degree of particle coalescence; and the results correlated well with other methods of characterization.