In 2009 Professor Guo and co-workers managed to pattern metal in such a way that volatile liquids could flow vertically upwards, and in 2010 they achieved the same effect using water on silicon. Now, they have managed to achieve upward flow on glass [Vorobyev and Guo, J Appl Phys (2010) 108, 123512].
Water is able to climb up the glass thanks to a form of capillary action, or wicking. A high-intensity femtosecond laser was used to pattern a glass plate using a series of pulses. The pulse power, duration and frequency have to be carefully chosen to obtain the desired effect. The result is a glass slide that is covered in a series of grooves, with a period of 100 microns. The microgrooves are covered with much smaller structures including nanocavities and pillars. These structures cause the glass surface to become hydrophilic, and so as the water spreads over the structures, it climbs upwards. Associate Professor Chunlei Guo explained to Materials Today, “Many materials are hydrophilic, so they have some wicking effect, but not at the strength even close to what we have demonstrated”. “We use the word superwicking to imply this extraordinarily strong wicking/hydrophilic effect”.
Guo and Vorobyev believe that the superwicking action is “due to combined capillary effects of open microgrooves and finer structures” [J Appl Phys (2010) 108, 123512]. However further study is required in order to fully understand the fundamental mechanism behind the phenomenon.
On silicon such a phenomenon could lead to a new method of processor cooling. Instead of using fans to extract heat from microchips, volatile liquids flowing over the surface could perform the same task; without dust accumulation and the possibility of mechanical failure. But glass is also an incredibly important material that is used in many fluidic devices and display technologies. Guo is hopeful that their research will lead to innovations in nano-/micro-fluidics, chemical and biological sensors, lab-on-chip technology, and biomedicine. There is also the possibility of a “self-cleaning mechanism for window glass”.
Stewart Bland