Droplet deposition and evaporation dynamics on chemically and topographically patterned surfaces

Inkjet printing is a promising alternative technique for the fabrication of functional devices such as organic light emitting diode displays. However, with ever increasing requirements for finer display resolutions, it becomes increasingly challenging to precisely position inkjet printed droplets. Even once the droplet is in the required location, there are challenges in achieving a uniform particle deposit of the functional material, once the solvent evaporates.

In this thesis, a multiphase lattice Boltzmann method is used to investigate the deposition processes of droplets deposited into idealised pixel geometries (square cavities). Specific attention is given to droplets deposited with positioning errors, to see which factors have the greatest influence on the droplets ability to self-align. Additionally, the model is coupled with an energy equation to investigate cavity properties on evaporation rate, internal flows, and particle deposition.

A review of different multiphase models leads to the choice of the pseudopotential method, as recent developments allow for the simulation of moderate density ratios, thermodynamic consistency, and the ability to couple with an energy equation to simulate thermal flows with phase change. Implementation is then discussed, with attention given to parallelising the multiphase algorithm to run on high-performance computers.

Different wetting models are evaluated, and a new model is suggested, which allows for additional control of adhesive forces over the liquid-vapour interface. Furthermore, the importance of boundary treatment in computing the pseudopotential forces is highlighted.

The new wetting model is used to explore the limits of positioning error for the deposition of droplets into square cavities. A regime map is suggested which highlights the conditions required for print success, relating droplet size, cavity size, and printer positioning errors.

Finally, investigations of evaporation in heated square cavities show the influence of receding contact angle on evaporation rate, internal flows, and particle deposition.