An artist's depiction of the liquid-like layer of molecules repelling water droplets. Credit: Ekaterina Osmekhina/Aalto University
Key points:
- Researchers have created the most water-repellent surface in the world.
- The new hydrophobic surface contains highly mobile molecular layers that are covalently tethered to a silicon substrate.
- The technique has many potential applications, ranging from de-icing to self-cleaning surfaces.
A study recently published in Nature Chemistry reveals how researchers developed a new mechanism to make the slipperiest liquid surface in the world. The discovery enables scientists to study droplet slipperiness at the molecular level and apply this knowledge to many household and industrial technologies.
Researchers created a droplet-repellent surface using a specially-designed reactor. These hydrophobic surfaces contain molecular layers that are covalently tethered to the substrate while remaining highly mobile. The liquid-like layer of molecules—called self-assembled monolayers (SAM)—exists on top of a silicon surface.
“Our work is the first time that anyone has gone directly to the nanometer-level to create molecularly heterogenous surfaces,” said lead author Sakari Lepikko of Aalto University.
By calibrating conditions inside the reactor, the research team could control the extent to which the monolayer covered the silicon surface. At low SAM coverage, water flowed freely between the molecules of the SAM and slid off the surface. Similarly, when SAM coverage was high, water stayed on top of the SAM and slid off just as easily. Intermediate coverage levels resulted in water adhering to the SAMs and sticking to the surface.
Looking ahead, the team plans to experiment with the self-assembling monolayer setup in order to improve the layer itself. Currently, the SAM coating is very thin and disperses easily after physical contact. By experimenting with the setup, researchers can create durable practical applications.
“Things like heat transfer in pipes, de-icing, and anti-fogging are potential uses,” explained Lepikko. “It will also help with microfluidics, where tiny droplets need to be moved around smoothly, and with creating self-cleaning surfaces. Our counterintuitive mechanism is a new way to increase droplet mobility anywhere it’s needed.”