New applications in studies of waterborne coatings by atomic force microscopy

Atomic force microscopy (AFM) is rapidly emerging as an important tool for coatings characterization. We report several new applications of AFM of particular value to the development of improved waterborne coatings systems. First, an AFM method was developed to quantitatively assess the extent of coalescence and film formation for latex films by measurement of particle number density of protruding (uncoalesced) particles in dried coatings. Second, the use of topographic imaging to evaluate environmental (temperature) effects on film formation was investigated for a waterborne latex system. Finally, specular gloss of waterborne epoxy coatings was studied by AFM and optical measurements, and topographic features analyzed using power spectral density calculations were found to correlate with optical gloss measurements. Mechanisms for gloss reduction over time (particularly in early pot life coatings) were elucidated in the studies. Further applications in coatings studies will be driven by the development of new modes of AFM (friction force, force modulation, and phase contrast) that can be used to map mechanical properties (friction, stiffness, and adhesion) while simultaneously imaging topography. Examples of the use of the phase contrast mode to identify chemically different domains in early pot life waterborne epoxy coatings are presented.