We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not an Insider? Subscribe now for unlimited access to online articles.

Intelligent Machines

No More Thumbprints

New chemistry and microsurfaces have led to super oil-repellent materials that are self-cleaning.

Researchers have made materials that repel oil and are able to clean themselves without the help of soap and water. What’s more, the researchers describe exactly how the materials work, which could help others design similar materials. This could lead to a range of applications, including fingerprint-shedding cell-phone displays. The researchers, from MIT and the Air Force Research Laboratory at Edwards Air Force Base, in CA, describe their results in the current issue of Science.

Good-bye, soap: Oil droplets bead up on a new, microstructured, oil-repellant, self-cleaning material.

Making super oil-repellant materials has been one of the great challenges in materials science, says Jeffery Youngblood, a professor of materials engineering at Purdue University, who was not involved in the research. Researchers have been able to make super water-repellant materials that cause water to bead up and form near-spherical droplets that easily roll or even bounce off surfaces. But oil has much lower surface tension than water does, so it has a greater tendency to spread over and cling to surfaces. That makes super oil-repellant materials, also called superoleophobic materials, difficult to create.

“Before now, superoleophobic materials have been a pipe dream,” Youngblood says. “As far as I know, no one has seen this type of oleophobicity before.” In the past, it’s been possible to make oil bead up on a surface, but the oil remained stuck, unable to slide off, Youngblood says.

The MIT and Air Force Research Laboratory researchers overcame the obstacles to super oil-repellant materials by combining two advances. First, the Air Force researchers developed a material that’s something like a super Teflon. Fluorine chemical groups in Teflon help make it repellant, says Gareth McKinley, a mechanical-engineering professor at MIT who is involved with the work. The Air Force researchers developed a molecule with a structure that incorporates much more fluorine. Adding this molecule to a material makes it more repellant to liquids.


But the chemistry of the material isn’t enough to make it super oil repellant. The researchers at MIT also changed the microscopic structure of the material in a way that traps air near the surface, so that oil on the material is suspended partly on air, which prevents the oil droplets from sticking to the surface, Youngblood says. The resulting material was so oil repellant that oil, which normally clings to surfaces, actually bounced off instead (see this video).

The researchers made the structure in two ways. For the first, they used a process called electrospinning to form microscopic threads of the fluorinated material. The threads formed a fibrous mesh that traps air. In part to study the mechanisms involved, the researchers also etched silicon wafers to form arrays of mushroom-shaped pillars in which air is trapped under the cap of the mushroom shape.

Structuring the surface of just about any type of material in this way will make it more repellant to oil. But if too much force is applied, the air can get pushed out, McKinley says. Adding the fluorine groups cause the material to resist this force much more, making it more practical.

Having created the materials, the researchers then studied the details of what makes them work. As a result, the researchers were able to outline ways to make super oil-repellant structures, describing what sort of chemical properties, combined with what kind of microscopic shapes, are necessary to create them. They described how the liquid interacts with the surface of a material, and how this changes according to the structure of the surface and the presence of air.

Using these rules, the researchers were able to tune the properties of the material. In one example, they were able to make the materials repel water but not oil–something that could be useful for filtering water out of fuel (see this video). By following these rules, researchers may be able to develop even better materials that are more oil repellant, cheaper to make, and even transparent. The last feature could lead to a number of applications, including self-cleaning displays–something that cell-phone manufacturers have been working on for years.

Cut off? Read unlimited articles today.

Become an Insider
Already an Insider? Log in.

Uh oh–you've read all of your free articles for this month.

Insider Premium
$179.95/yr US PRICE

More from Intelligent Machines

Artificial intelligence and robots are transforming how we work and live.

Want more award-winning journalism? Subscribe to Insider Plus.
  • Insider Plus {! insider.prices.plus !}*

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus the digital magazine, extensive archive, ad-free web experience, and discounts to partner offerings and MIT Technology Review events.

    See details+

    What's Included

    Unlimited 24/7 access to MIT Technology Review’s website

    The Download: our daily newsletter of what's important in technology and innovation

    Bimonthly print magazine (6 issues per year)

    Bimonthly digital/PDF edition

    Access to the magazine PDF archive—thousands of articles going back to 1899 at your fingertips

    Special interest publications

    Discount to MIT Technology Review events

    Special discounts to select partner offerings

    Ad-free web experience

You've read all of your free articles this month. This is your last free article this month. You've read of free articles this month. or  for unlimited online access.