Stratification Mechanism in the Bidisperse Colloidal Film Drying Process: Evolution and Decomposition of Normal Stress Correlated with Microstructure

Abstract

The evolution of the normal stress and microstructure in the drying process of bidisperse colloidal films is studied using the Brownian dynamics simulation. Here, we show that the formation process of small-on-top stratification can be explained by normal stress development. At high Pe L’s, a stratified layer with small particles is formed near the interface. The accumulated particles near the interface induce the localization of normal stress so that the normal stress at the interface increases from the beginning of drying. We analyze this stress development from two points of view, on the global length scale and particle length scale. On the global length scale, the localization of normal stress is quantified by the scaled normal stress difference between the interface and substrate. For all Pe L’s tested in this study, the scaled normal stress difference increases until the accumulation region reaches the substrate. After the maximum, the stress difference remains at the maximum at lower Pe L’s, while it decreases at higher Pe L’s. The microstructural analysis shows that this stress development is explained through the evolution of the particle contact number distribution at the interface and substrate. On the particle length scale, we derive the scaled local force applied to each type of particle by decomposing the local normal stress. At high Pe L’s, the scaled local force for the large particle is large compared to that for the small particle near the interface, indicating that the large particles are strongly pushed away from the interface. Associating the volume fraction profile with the local force field, we suggest that the strong scaled force for the large particle is attributed to the significant increase in the average number of small particles in contact with large ones. This study has significance in probing the drying mechanism of bidisperse colloidal films and the stratification mechanism.

Size-Dependent Dried Colloidal Deposit and Particle Sorting via Saturated Alcohol Vapor-Mediated Sessile Droplet Spreading

“…Recently, Upadhyay and Bhardwaj reported geometry- and gravity-assisted particle sorting of colloidal particles upon drying of the capillary bridge. Furthermore, the self-assembly of a binary mixture of soft colloids was looked at by Jose et al Recently, dynamic density functional theory-based investigations on drying and stratification (self-segregation) dynamics of colloidal films on planer surfaces have attracted significant attention of researchers, , owing to their importance in achieving layered deposits. Apart from theory, efforts were devoted to investigating the above-mentioned stratification process to delineate the effect of evaporation rate and particle interactions, corroborated by diffusion-based theories.…”

High-Speed Li-Ion Battery Manufacturing Process Applying the Dewatering Concept

“…In an effort to increase the speed of electrode manufacturing, increasing the coating and drying speeds is a logical approach. However, increasing the drying speed can lead to binder migration and a subsequent decrease in the mechanical properties and electrochemical performance of the battery. − Additionally, it can cause surface defects and stratification, , which can affect the electrode microstructure. To reduce the energy and time required in the drying process, increasing the solid content of the slurry may seem to be a viable option.…”

Inducing stratification of colloidal mixtures with a mixed binary solvent

“…22 Fortini et al later discovered the unexpected small-on-top stratification in the case of extremely fast drying rates. 23 This discovery has triggered a series of experimental, [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] theoretical, [40][41][42][43][44][45] and computational [46][47][48][49][50][51][52][53][54][55][56][57][58] studies to reveal the underlying physical mechanism. It is now generally believed that the small-on-top stratification can be explained on the basis of diffusiophoresis, where colloidal particles are driven by the concentration gradient of other solutes (e.g., another type of particles) in the suspension.…”