Smart surface enables advanced manipulation of droplets

July 25, 2017, University of British Columbia
Applying low voltage to a nanostructured copper surface changes its oxidation state, and hence its ability to attract and repel liquids. Credit: University of British Columbia

For many years, engineers have sought to create a special kind of surface: one that can both repel and absorb liquids, and whose ability to do so—its "wetting behaviour"—can be quickly and precisely controlled. The technology would have a wide range of potential applications, from water filtration and biomedical devices to liquid optical lenses and lab-on-a-chip systems.

Such a "smart " has now been developed by researchers at the University of British Columbia. Inexpensive, scalable and powered by just a conventional electric battery, the copper-based surface changes from being very water-repellent (superhydrophobic) to very water-absorbent (superhydrophilic) as electric potential is applied.

"When tiny voltages are applied to the surface, that initially roll off stick to it more and more tightly," says Ben Zahiri, the study's co-lead author. "By changing the magnitude of the voltage and how long it is applied, we can easily control the angle that each droplet forms with the surface and how quickly this happens."

When the is removed, the droplet retains its shape and remains pinned in place.

Other groups have modified the wetting behaviour of copper surfaces using stimuli like heat, UV radiation and X-rays. But in order to achieve this, the required temperatures are high—up to 300 degrees Celsius—and the required exposure times are long—from tens of minutes to days. This makes them impractical for a number of consumer and industrial purposes.

In contrast, the electrical stimulus used by the UBC team modifies wetting behaviour rapidly (from a few seconds to a few minutes) and reversibly, at voltages found in everyday batteries (less than 1.5 V). It does so by changing the oxidation state of the copper surface, which contains a mixture of hydrophilic CuO and hydrophobic Cu2O: as copper loses electrons, it becomes less attracted to water.

The ability to control surface wettability could be useful wherever droplets, or solid particles absorbed by droplets, need to be manipulated, including microfluidic devices and hazardous material handling systems. It also offers advanced self-cleaning capabilities by enabling the controlled roll-off of fluids.

UBC-developed smart surface offers fast and reversible surface wetting properties-from superhydrophobic (water-repellant) to superhydrophilic (water-attractive) using a small voltage that could be supplied by conventional batteries. Credit: University of British Columbia

Although the UBC team chose to investigate copper because it is cheap, abundant and one of the most commonly used metals in the world, Zahiri believes that the electrochemical manipulation of other metals, metal oxides and mixed oxides may yield similarly promising results. As for the liquid, any conductive fluid, such as blood, could be used.

"These findings could open up a new area of exploration for smart surfaces," says UBC mechanical engineering professor Walter Mérida, who supervised the work.

This study was recently published in Advanced Materials Interfaces.

Explore further: Even droplets sometimes take the stairs

More information: Beniamin Zahiri et al, Active Control over the Wettability from Superhydrophobic to Superhydrophilic by Electrochemically Altering the Oxidation State in a Low Voltage Range, Advanced Materials Interfaces (2017). DOI: 10.1002/admi.201700121

Related Stories

Even droplets sometimes take the stairs

July 11, 2017

Sometimes, liquid drops don't drop. Instead, they climb. Using computer simulations, researchers have now shown how to induce droplets to climb stairs all by themselves.

Movable microplatform floats on a sea of droplets (w/ video)

December 16, 2016

Microelectromechanical systems, or MEMS, are tiny machines fabricated using equipment and processes developed for the production of electronic chips and devices. They've found a wide variety of applications in today's consumer ...

Recommended for you

Information engine operates with nearly perfect efficiency

January 19, 2018

Physicists have experimentally demonstrated an information engine—a device that converts information into work—with an efficiency that exceeds the conventional second law of thermodynamics. Instead, the engine's efficiency ...

Team takes a deep look at memristors

January 19, 2018

In the race to build a computer that mimics the massive computational power of the human brain, researchers are increasingly turning to memristors, which can vary their electrical resistance based on the memory of past activity. ...

Artificial agent designs quantum experiments

January 19, 2018

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

tedbooth10
not rated yet Jul 26, 2017
It the depth of a sphere can be controlled through voltage, so I wonder if the spheres can be used for photonics in analogy to drilled spherical-like surfaces in 1-dimensional photonic silicon crystals. So the water droplets looking at it from below the surface would look the same as a conventional photonic silicon surface (drilled) from above. I saw also dielectric nanoparticles can be suspended in droplets, I suppose making an analogy to dielectrics. The application I'm thinking is the recent photonic quantum gate made by MIT that consists of a 1d row of decreasing size drilled spheres, then a dielectric, then a row of increasing size drilled spheres in a silicon crystal with dielectric at the center.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.