09/05/2012: Transport Phenomena in Droplet-Surface Interactions

Transport Phenomena in Droplet-Surface Interactions: From Nanoengineering to Frost Formation

Dr. Manish K. Tiwari

Mittwoch, 9. Mai 2012
Hörsaal ML H 44

Liquid droplets are ubiquitous in our daily life from the shower curtain to the drips of the coffee machine. As fluid mechanics objects their formation and dynamics are strongly influenced by surface effects and surface (capillary) forces. Understanding droplet formation and droplet-solid interactions is crucial to interpreting not only the natural phenomena such as rain drop size dis- tribution, but numerous technologically relevant applications.

In this colloquium, I will talk about two droplet based applications. First, I will present a tech- nique to print nanoscale droplets of nanoparticle suspensions. The droplets are formed using electric field assisted actuation of liquid through a ~micrometer size print nozzle. The individual drops form nanoparticle deposits on the substrate and by printing a series of drops, we can form lines and pillars of the nanoparticle clusters. We have also extended the technique to print three- dimensional (3D) nanostructures, which marks a clear advancement over the commonly em- ployed lithography based techniques for nanofabrication. In the second application, we employ droplets to evaluate systematically nanoengineered, highly liquid repellent surfaces with hierar- chical micro-to-nanoscale roughness. These artificial surfaces mimic the hierarchical morpholo- gy of the lotus leaf and the other natural surfaces with strong liquid repellency. Given their water repellency, one may intuitively expect these surfaces to also possess ice-repellency and low ice- adhesion. We show, however, that ice-repellency of a solid surface can be seriously impaired by minor changes in the environmental conditions such as air flow or humidity. A deeper analysis also reveals that droplet freezing is quite dramatically affected by its simultaneous evaporation. The results not only highlight the richness of physics in a simple freezing problem, but also offer some guidelines on the future design of surfaces with low ice-adhesion.