Material Elixir for Oily Water

Oil and water do mix – all too often. And they’re not so easy to separate. Just ask the research scientists trying to develop next-generation water-filtration technologies to do it.
But with the 21st century toolsets of nanotech and chemistry, they promise to overcome vexing problems of cost-effectively removing oil agents from drinking water.
Researchers at Purdue University have developed a new, durable membrane material that does double duty: it separates oil from water (at a 98 percent rate) and cleans itself to prevent clogs.

Those kinds of purification numbers and characteristics offer a unique filtration material well suited for environmental cleanup, water purification and industrial applications.

The material is a modified polyethylene glycol. Water molecules are attracted to it and when they pass through, the oil molecules get trapped.

But the oil doesn’t stick and can later be skimmed off in a self-cleaning flush, making for longer life. The Purdue researchers also say the same technology could be used to create antifogging goggles and self-cleaning eyeglasses by not allowing water to form beads on surfaces.

A new way to separate oil and water.
(Photo: Purdue School of
Materials Engineering)

The material is still in the experimental stage but it could be built into an experimental cross-filtration device that does not require a lot of energy to push the water through it. This is a big shortcoming to many filtration systems today.

There is also the potential to use the technology in a gravity-fed system, which would be suitable for remote villages and rural environments without electricity.

To date, the researchers have only tested diesel or hexadecane fuel but the team has plans to test other oils such as benzene toluene zylene.

Meanwhile, an MIT research team led by chemical engineer Robert Cohen and mechanical engineer Gareth McKinley has created what it claims are the first “superoleophobic,” or oil-repellant surfaces. They used a polymer developed by the Air Force that contains large numbers of oil-repelling fluorine groups. In order to transform the material into oil resistance, the MIT researchers used lithography to pattern the polymer with overhanging microstructures. In doing so, they gave the material air pockets, which helps suspend liquids and prevent them penetrating to the surface.

The MIT material has extremely low surface energy, in fact lower than the Purdue team’s material. But Purdue’s material has shown superior performance at cleaning oil from the surface of the material.

“Our materials provide for a flat surface where water ‘sees’ a wettable surface and the oil ‘sees’ a non-wettable fluorinated surface,” said Jeff Youngblood, assistant professor of materials engineering at Purdue University. “This is pretty good because if you don’t modify the glass filters with our material, essentially all the oil goes through. If you modify it with our material, then almost none of the oil goes through.”

All of which should eventually become valuable in long-term water-infrastructure developments like the Water Infrastructure Network, which is a a coalition of locally elected officials, drinking water and wastewater service providers, state environmental and health administrators, engineers and environmentalists. The group is urging water-industry professionals to contact their representatives in Congress to push passage of a $20 billion package for water infrastructure. Lee Bruno

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