(287c) Stress Development in Drying Aqueous Particulate Coatings

Defect-free particulate coatings are an essential component of many consumer and industrial products. In addition to coating formulation and deposition, drying is a key stage in the coating process for determining coating microstructure, properties, and defects. Drying defects, such as cracking, curling, and delamination originate from stress build-up within the coating layer. Through cantilever beam deflection and Cryo-SEM, prior work related stress to capillary pressures that form between particles within a drying particle network. Water-born hard particulate suspensions are especially prone to cracking whilst drying. The present work investigates the drying of particulate suspensions that result in crack-free and cracked coatings. Aqueous suspensions prepared from from monodisperse silica (D₅₀ = 0.9 μm) or polydisperse zinc oxide (D₅₀ = 0.4 μm) particles experienced up to ~1 MPa of stress while remaining crack free. Likewise, cracking coatings were prepared from suspensions of smaller monodisperse silica (D₅₀ = 0.3 μm) or by thick application of the polydisperse zinc oxide suspension. Evidence of stress release upon evaporation and fracture is observed through cantilever beam deflection and simultaneous surface imaging. This poster will address continued efforts towards understanding stress and fracture within the coating layer.