When rain falls on a lotus leaf, the leaf doesn’t get wet. Thanks to its special structure, the water drops roll off without wetting the surface. Artificial materials can be made water-repellent, too. It is, however, extremely challenging to produce a surface with switchable wetting. Now, a research team from TU Wien, KU Leuven and University of Zürich has managed to manipulate a surface of a single layer of boron nitride in such a way that it can be switched back and forth between states with high and low wetting and adhesion.
Hexagons making waves
One of the most interesting physical properties of a surface is its stiction or static friction” says Stijn Mertens (Institute of Applied Physics at the Vienna University of Technology, and associated with KU Leuven in Belgium). „This force has to be overcome for an object on the surface to start sliding.” The nanostructure of the surface determines its stiction to a large extent: the details of the contact between the surface and another object (for example, a drop of liquid) depend on the geometry of its atoms and other properties. This in turn is crucial for adhesion, stiction and wetting. The relationship between stiction and wetting, however, is so far only poorly understood.
“Just as the material graphene consists of only one layer of carbon atoms, our boron nitride — which contains as many boron as nitrogen atoms — has a thickness of only one atomic layer”, explains Thomas Greber from the Physics Institute at the University of Zürich. This ultrathin layer can be grown on a rhodium single crystal. The atoms on the rhodium surface and in the boron nitride form a hexagonal pattern, but the distances between the atoms in the two materials are different. Thirteen atoms in boron nitride take the same space as twelve rhodium atoms, so that the two crystals do not fit together perfectly. Because of this mismatch, the boron nitride hexagons must bend, they appear as a frozen wave with a wavelength of 3.2 nanometres and a height of about 0.1 nanometres.
Precisely this two-dimensional nanowave influences the wetting of the surface by water”, says Stijn Mertens. In any case, the boron nitride superstructure can be made flat with a simple trick: by putting the material in acid and applying an electrical voltage, hydrogen atoms creep under the boron nitride layer and change the bond between nitrogen and rhodium. This makes the boron nitride flat. Suddenly the adhesion of a water drop on the surface changes dramatically – even though the drop is 100’000 times bigger than the tiny waves in the boron nitride. If the voltage is decreased, this effect is reversed: „We can switch the surface again and again between these two states”, explains Stijn Mertens.
The drop-measuring machine
To investigate the wetting of the surface and apply the voltage at the same time, an instrument was built specially for this purpose, in which a liquid drop is brought on the surface through a very thin glass tube. The drop is made bigger and smaller while at the same time its shape is recorded. Whether the drop shape is flat or more rounded depends on the properties of the surface.
Concepts to switch the wetting of a surface forth and back have been around for a while. For example, organic molecules that change their shape with light of a certain colour can be attached to the surface. However, such molecules are much more complex and fragile than the materials studied here. „Our surface consists of only a single layer of atoms, is completely inorganic and does not change even if we heat it in vacuum to 1000 °C”, agree Stijn Mertens and Thomas Greber. „This means that this material could also be used for applications where organic molecules would long be destroyed, ranging from daily life to space travel.”
Learn more:Â Shaping drops: Control over stiction and wetting
The Latest on: Switchable wetting
[google_news title=”” keyword=”Switchable wetting” num_posts=”10″ blurb_length=”0″ show_thumb=”left”]
via Google News
The Latest on: Switchable wetting
- Doja Cat’s Met Gala Look Was Drenched in Hair Gel and Wateron May 7, 2024 at 4:47 am
She maintained the wet-like effect in her makeup look as well ... Event The “Kiss Me More” singer went on to explain that she wanted to drastically switch things up from last year’s extravagant look, ...
- Doja Cat on why she wore a wet t-shirt to the Met Galaon May 6, 2024 at 5:32 pm
Doja Cat explains why she wore a wet t-shirt to the Met Gala. Copyright 2024 The Associated Press. All Rights Reserved.
- Davey Todd: Switch to BMW can power me to Superbike glory at NW200on May 4, 2024 at 11:00 pm
Davey Todd believes his switch to BMW machinery this year will provide the missing link in his quest for a maiden Superbike victory at the Briggs Equipment North West 200.
- Dyson V15s Detect Submarine Wet Dry Vacuum Cleaner reviewon May 4, 2024 at 7:01 pm
A powerful, all-in-one, vacuum cleaner with a wet-dry attachment that washes your floors and does a decent job — although don’t ditch your mop and bucket just yet.
- Portland Braces for Continued Rainfall, NWS Predicts Wet Week Aheadon May 2, 2024 at 7:03 am
A forecast predicts a rainy period for Portland with occasional showers and high precipitation, including a brief sunny break on Thursday before rain resumes over the weekend.
- Met Eireann say Ireland to ‘turn warmer’ for Bank Holiday weekend as big switch expectedon April 29, 2024 at 2:05 am
IRELAND is set to warm up again for the May Bank Holiday weekend after a "wet start" to the week. Forecaster Deirdre Lowe advised the wet conditions are set to take a turn mid-week. The week begins ...
- Tineco Reinvented Cleaning with the SWITCH S7: A Two-Faced Solutionon April 28, 2024 at 7:51 pm
The SWITCH S7 cleverly combines the functions of a wet and dry vacuum cleaner and a cordless vacuum cleaner, offering a complete solution for optimal cleaning of the entire house and all floors.
- 18 Tortilla Alternatives To Switch Up Your Wrapson April 27, 2024 at 7:15 am
If you've ran out of tortillas or want to switch things up for your next tasty wrap, grab a rice paper or roti instead. Love those ideas? We have more for you.
- The Kick Switch is a Hands-Free Garbage Disposal Switch for a Safer and Cleaner Kitchen Experienceon April 27, 2024 at 6:04 am
Live on Kickstarter, The Kick Switch is the sleek, under-the-sink switch that lets users control the garbage disposal hands-free. The Kick Switch, the revolutionary new hand-free, under-the-sink ...
- The 6 Best Shop Vacs To Pick Up Heavy Debris And Wet Messeson April 25, 2024 at 11:19 am
The best shop vacs feature a wide nozzle and a strong engine, enabling them to efficiently clean up wet and dry messes around your home. Here are our top recommendations.
via Bing News