Many examples for liquids on fibers are known in nature. Just think about dew droplets on spider webs that you can observe during a walk in the morning. Indeed, humidity is collected on the fiber as droplets, as the liquid surface can be minimized this way. This phenomenon, which can also be observed for a stream of water flowing out of a faucet, is named the Rayleigh-Plateau instability. "All systems drive towards their energetic minimum, and that is the droplet shape in this case," says Sabrina Haefner, a physicist in the research group of Karin Jacobs. This instability can be very useful in very dry and remote regions of the world. For example, in Chile's Atacama desert, the getting drinking water is essential for the locals, and they harvest water from humidity by means of fiber nets.
The team of physicists tested this for liquid films supported by uncoated and Teflon-coated fibers. On uncoated fibers, the liquid film moved rather slowly, and droplet formation took longer than on coated fibers, where the liquid film was able to slip. "In line with mathematical models, these experiments allow for quantifying ’slippage’ of liquid films and to precisely predict the dynamics of the droplet formation process," says Sabrina Haefner from Saarland University. The team of researchers agrees: their results are very important for the design of novel fiber coatings. Besides the German researchers, teams from McMaster University in Hamilton, Canada, and the ESPCI in Paris, France were involved in this project.
(© Saarland University, AcademiaNet)