Mother Nature, the fairy godmother of many new coatings technologies, has yet another protective trick up her sleeve.
The inspiration this time comes from the gravity-defying water strider, which has led Chinese scientists to develop a coating for a tiny device that can repel oil underwater.
|By imitating how a water strider insect (left) floats between air and water, researchers created a device (right) that floats between oil (pink) and water (colorless), aided by an oil-repellent copper oxide coating. |
The hope is that a veritable army of the critters can one day clean up oil spills.
That’s the theory behind “Bioinspired Oil Strider Floating at the Oil/Water Interface Supported by Huge Superoleophobic Force,” recently published in the American Chemical Society’s journal ACS Nano.
“Oil pollution to aquatic devices, especially to those oil-cleaning devices and equipment-repairing robots during oil spill accidents, has drawn great attention and remains an urgent problem to be resolved,” write Shutao Wang and colleagues from the Chinese Academy of Sciences.
“Developing devices that can move freely in an oil/water system without contamination from oil has both scientific and practical importance.”
Like many scientists, the team turned to nature to see who or what was already best at doing the task at hand. Such “bioinspired” coatings have gained a niche of their own in recent years.
The researchers’ model became the water strider, an insect that floats—improbably and uniquely—on the water’s surface by using “superhydrophobic supporting force received by its legs,” the team writes.
Replicating those principles, the scientists developed their own “oil strider” that can skate smack at the oil/water interface without being contaminated by the oil.
The secret, in part, is the oleophobic (oil-repellant) coating that Wang and his colleagues developed for the 5 cm-long device’s legs.
Most oleophobic coatings don’t work if they get wet—a decided drawback for the oil-spill scenario. But Wang’s team engineered the coatings and other elements to make it work.
“We prepared the micro/nanohierarchical structured copper-oxide-coated copper wires, acting as the artificial legs of oil strider, by a simple base-corrosion process,” the researchers report. The copper-wire “legs” were coated with a rough nanocoating that simulated the texture of the insect’s legs.
“The surface structures and hydrophilic chemical components of the coatings on copper wires induced the huge superoleophobic force at the oil/water interface, to support the oil strider from sinking into the oil.”
The supporting force is mainly composed of three parts: the buoyancy force, the curvature force, and the deformation force.
Skating to Success
The pseudo-strider skated nicely in a lab container filled with oily water, the scientists said. Bigger testing grounds await.
Meanwhile, the team remains optimistic, writing: “We anticipate that this artificial oil strider will provide a guide for the design of smart aquatic devices that can move freely in an oil/water system with excellent oil repellent capability, and be helpful in practical situations such as oil handling and oil spill cleanup.”