Drying dynamics of drops of complex fluids

Abstract

Understanding the drying dynamics of complex fluids is of great importance to many industrial processes such as production of dry powders, ceramics and various pharmaceutical products. The characteristic of the final product depends on several parameters relating to the physicochemical properties of the evaporating solution, atmospheric conditions and the transport properties of the substrate. Thus, it is important to understand the dominant mechanisms controlling the drying dynamics of dispersions. In this dissertation, several parameters such as the particle size, particle concentration and initial droplet volume have been shown to influence the drying kinetics of colloidal droplets and the morphology of the final dried grains. The observed morphological differences were shown to be the result of the competition between diffusion and convection during drying. We combine these experimental data into a dimensionless Péclet number to show that the drying behaviour is dependent on all the parameters. Furthermore, the grain morphology can differ due to the presence of formulation additives such as surfactants. In such case, surface tension driven instability can result in breakup of the evaporating droplets which in turn leads to hollow dried grains. This pathway highlights the importance of the surface tension forces of droplets in maintaining stable interfaces against external forces. Additionally, in this dissertation, the effect of the substrate transport properties on the drying dynamics and the resulting disposition patterns were investigated. In this regard, graphene based membranes were fabricated with well-defined properties and several rounds of droplet evaporation experiments were conducted using these membranes as substrate. This enabled us to delineate how the drying dynamics and patterns of solute deposition is influenced by the physicochemical properties of the substrate. The results reported in this dissertation shed new insight on the physics of droplet drying and its complex dynamics. The results of this dissertation have been published in 3 peer-reviewed journal papers.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Nima Shokri (Supervisor) & Alessandro Patti (Supervisor)