Turning superhydrophobic surfaces into printers

It is well-known that static wetting properties of solid surfaces can be modified by microscopic patterning of flat surfaces, using mechanical or chemical methods. In particular, the “lotus effect” (superhydrophobic surfaces to which liquids do not adhere) can be achieved by adding periodic arrays of micron-sized pillars or holes to an initially partially wetting surface. Similar structures are also present on gravure clichés which are used in modern industrial printing. Combined with an externally switchable electrowettingn(EW) functionality, such surface features would allow dynamic control of ink affinity to different regions on the and also offer control over ink transfer to a printed substrate (plastic or glass) and opens the possibility of pushing the printing resolution down to scales previously reserved to slow, expensive methods like photo- or nano-imprint lithography.

The aim of the project is to demonstrate that the wetting properties - in particular the filling - of small holes engraved into a hydrophobic surface can be controlled by EW. The concept is illustrated in the figure above. Holes (µm depth) will be manufactured using lithography techniques from a hydrophobic dielectric material applied to a flat glass substrate, previously coated with a thin film ITO (indium tin oxide) layer. “Ink” (low viscosity liquid, e.g. water) will be applied by dip coating from a bath: in the absence of a voltage, the liquid does not “stick” to the small surface features, while when a voltage is applied, electrowetting effectively increases the affinity of the liquid on the cliché and the holes will fill with ink. The actual work will consist of:


Fabrication and characterization of structured surfaces


Investigation of the filling dynamics using high-speed imaging and various microscopy techniques (differential interference contrast (DIC), reflection contrast interference microscopy (RCIM), fluorescence microscopy).


Modeling of the wetting process of structured surface (e.g. as a function of geometric parameters, surface tension, voltage)

Further information:

Frieder Mugele (f.mugele@utwente.nl)