in Wiley Online Library (wileyonlinelibrary.com).Key microstructural properties of particulate coatings such as porosity and particle order are established during drying. Therefore, understanding the evolution of particulate distributions during drying is useful for designing coating properties. Here, a 1D model is proposed for the particle distribution through the coating thickness at different drying times and conditions, including Brownian diffusion, sedimentation, and evaporation. Effects of particle concentration on diffusion and sedimentation rates are included. Results are condensed onto a drying regime map which predicts the presence of particle surface accumulation or sediment based on two dimensionless numbers: the Peclet number and the sedimentation number. Cryogenic scanning electron microscopy (cryoSEM) is used to image the transient particulate distributions during the drying of a model system comprised of monodisperse silica particles in water. Particle size and evaporation rates are altered to access various domains of the drying map. There is good agreement between cryoSEM observations and model predictions.
Convective assembly is a coating method to fabricate thin films with ordered particle structures that can be used extensively for biochemical sensors, data storage devices, optical devices, and other applications. The fluid flow into or through the close-packed region causes the convective assembly, and it is important to understand the formation mechanism of the close-packed region. In this paper, the length of the close-packed region was predicted, and the dimensionless coating thickness as well as the dimensionless length of the close-packed region was found to be the functions of only three dimensionless variables: two capillary numbers and the initial volume fraction. From the modeling results, coating process regime maps that predict the dimensionless coating thickness in terms of the dimensionless variables were created. In addition, the length of the close-packed region was measured under various coating conditions to validate the model prediction. The experiments firmly supported the model predictions.
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