(462d) Microstructure and Stress Development in Particulate Coatings

A wide variety of products, including paints, adhesives, membranes, fuel cell components, printed electronic circuits and newsprint, are produced by liquid-applied coating and printing processes. A coating or printing process has two main steps: deposition of a liquid (e.g., solution, dispersion) onto a substrate and solidification, typically by drying or curing, into a functional coating or printed patch. This talk will focus on our efforts to understand and characterize the changes in structure that occur during drying and the impact of these changes on stress development.  Two special techniques will be used: cryogenic SEM (cryoSEM) and stress measurement.  CryoSEM involves freezing coatings at different stages of drying, fracturing to reveal cross-sections, subliming for contrast and imaging with an SEM equipped with a cryostage.  CryoSEM reveals particle and water distribution through the thickness of a drying coating.  Coating stress is measured during drying using a cantilever beam measurement.  Walls built on the cantilever suppress lateral drying fronts, which simplifies the interpretation of stress development.  Results from aqueous dispersions of silica particles will be presented. Parallel cryoSEM and stress measurement experiments were carried out to understand the origin of stress development.  Additionally, using a variety of other coating dispersions, the effects of particle size, particle deformation and binder on particle distribution and stress will be presented.