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Subproject A04: Flow and Evaporation of Pure Liquids and (Nano-) Suspensions from Structured Coatings

The heat transfer during the impact of cold drops onto hot walls is determined by the hydrodynamics of spreading, rebounding or splashing. The outcome and hydrodynamics of the drop impact strongly depend on the wetting properties of the fluid at the surface of the solid substrate and on the substrate temperature.

During the drop impact on substrates with nanostructured coatings, in contrast to smooth surfaces, liquids can penetrate into the pores of the coating. As a result, rebounding or splashing can be prevented and the hydrodynamics of the droplet spreading is significantly influenced.

The aim of this project is to experimentally and theoretically investigate the mechanisms of droplet spreading, imbibition into porous structures and evaporation during the drop impact on substrates with porous coatings. The influence of the fluid properties, the morphology of the coatings and environmental parameters on these processes should be considered.

The experimental study involves drop impact experiments in an air-conditioned test cell. Heatable substrates are used, which are coated with nanofibers. With the electrospinning process, nanofiber mats can be made of different polymers and with variable parameters, e.g. fiber diameter and mat thickness. Pure liquids as well as binary mixtures have priority in the investigations in order to assess the influence of the fluid properties. Furthermore, the deposition behavior of particles in porous coatings is investigated by using (nano-) suspensions.

The accompanying theoretical investigation aims at both the isolated description of single processes and the development of an overall model, taking into account simultaneous processes.

CRC 1194 – Interaction between Transport and Wetting Processes, Project A04