A Review of Dispersion Film Drying Research

Abstract

Dispersion drying is an essential step in an enormous number of research and industry fields, including self-assembly, membrane fabrication, printing, battery electrode fabrication, painting, and large-scale solar cell fabrication. The drying process of a dispersion directly influences the structure and properties of the resulting dried film. Thus, it is important to investigate the underlying physics of dispersion drying and the effects of different drying parameters. This article reviews modeling studies of coating drying processes, along with corresponding experimental observations. We have divided drying processes into two conceptual stages. In the first drying stage, liquid evaporation, particle sedimentation and Brownian motion compete and affect the particle distribution during drying and thus in the final film structure. We have included a comprehensive discussion of the influences of drying parameters, such as evaporation rate, particle sizes and temperature, on the above competition and the resulting film structure. A drying regime map describing where different drying phenomena dominate was formulated based on the literature. We also extended our discussion to the practical applications of battery slurry drying an essential step in conventional battery electrode manufacturing. In the second drying stage, the physics of porous drying and crack formation are reviewed. This review aims to provide a comprehensive understanding of dispersion drying mechanisms and to provide guidance in the design of film products with favorable structures and properties for targeted practical applications.

Visualization of Porous Composite Battery Electrode Fabrication Dynamics for Different Formulations and Conditions Using Hard X-ray Microradiography

“…After the fluid front reaches the trailing edge of a coating and is unable to progress farther, fluid should flow in a qualitatively different way, and the influence of this boundary should propagate backward toward the leading edge. Finally, appreciable fluid flow might stop long before a coating is fully dry. We expect that solvent evaporation will usually decrease coating height, although the relationship between solvent evaporation and coating height and structure might become complicated near the end of the drying process . We also expect the influence of solvent evaporation to continue after there is no longer appreciable fluid flow, when the coating might be thought of as a damp solid rather than a complex fluid; since we were able to observe parts of the coatings through the beamline hutch window and stop experiments after the visible regions appeared dry, we expect that solvent evaporation was the last major influence to wane in our observations. Temperature increases from heating will subtly increase coating height through thermal expansion.…”

“…The gray regions above the high-density regions and below the air/coating interfaces are less concentrated coating regions, which we will refer to as “low-density.” We acknowledge that we are making these classifications of coating regions on the sole basis of initial appearance. We also note that the platform is positioned for observation about half a minute after the coating is produced, and the existence of the high-density regions so soon after casting is in conflict with many drying and consolidation models . We suspect that the high-density regions primarily contain relatively large particles for which Brownian forces have limited influence, and that the low-density regions primarily contain relatively small particles with colloidal behavior.…”

One Step Closer to Coatings Applications Utilizing Self-Stratification: Effect of Rheology Modifiers

“…Self-stratification of colloidal dispersions during drying is an attractive method to form multilayer coatings in a single pass. In model systems stratification has been achieved through several approaches such as diffusiophoresis, controlled aggregation, and harnessing differences in surface chemistry . However, in practice, colloidal formulations are complex fluids where the influence of each component on others is difficult to predict.…”

“…Drying multicomponent colloidal dispersions plays an essential role in a wide range of applications including decorative and protective coatings, photonic glasses, and electrode fabrication . In most cases, the distribution of components through the film is crucial to the film’s overall functionality.…”

“…However, controlling the distribution often requires multiple deposition steps. An alternate approach is self-stratification, where the assembly of components during drying allows formation of multilayer films in a single pass. ,, …”