MIT Develops Treated Surfaces That Can Actively Control How Fluids Move
Science & Technology

Engineers Develop Surfaces That Can Actively Control How Fluids or Particles Move

Picture reveals a water droplet sitting on a ferrofluid-impregnated floor, which has cloaked the droplet with a really skinny layer. Picture courtesy of the researchers.

Utilizing a microtextured floor, with bumps or ridges only a few micrometers throughout, engineers have developed a brand new method of constructing surfaces that may actively management how fluids or particles transfer throughout them.

Researchers at MIT and in Saudi Arabia have developed a brand new method of constructing surfaces that may actively management how fluids or particles transfer throughout them. The work would possibly allow new sorts of biomedical or microfluidic units, or photo voltaic panels that would mechanically clear themselves of mud and grit.

“Most surfaces are passive,” says Kripa Varanasi, an affiliate professor of mechanical engineering at MIT, and senior creator of a paper describing the brand new system in the journal Applied Physics Letters. “They depend on gravity, or different forces, to maneuver fluids or particles.”

Varanasi’s workforce determined to make use of exterior fields, resembling magnetic fields, to make surfaces lively, exerting exact management over the habits of particles or droplets shifting over them.

The system makes use of a microtextured floor, with bumps or ridges only a few micrometers throughout, that’s then impregnated with a fluid that may be manipulated — for instance, an oil infused with tiny magnetic particles, or ferrofluid, which might be pushed and pulled by making use of a magnetic area to the floor. When droplets of water or tiny particles are positioned on the floor, a skinny coating of the fluid covers them, forming a magnetic cloak.

Watch a water droplet get pulled throughout an “lively” floor designed by MIT researchers. Video: Melanie Gonick/MIT

The skinny magnetized cloak can then really pull the droplet or particle alongside because the layer itself is drawn magnetically throughout the floor. Tiny ferromagnetic particles, roughly 10 nanometers in diameter, within the ferrofluid may permit precision management when it’s wanted — resembling in a microfluidic system used to check organic or chemical samples by mixing them with quite a lot of reagents. In contrast to the mounted channels of standard microfluidics, such surfaces may have “digital” channels that might be reconfigured at will.

Whereas different researchers have developed methods that use magnetism to maneuver particles or fluids, these require the fabric being moved to be magnetic, and really sturdy magnetic fields to maneuver them round. The brand new system, which produces a superslippery floor that lets fluids and particles slide round with just about no friction, wants a lot much less power to maneuver these supplies. “This permits us to achieve excessive velocities with small utilized forces,” says MIT graduate pupil Karim Khalil, the paper’s lead creator.

The brand new strategy, he says, might be helpful for a spread of functions: For instance, photo voltaic panels and the mirrors utilized in solar-concentrating methods can shortly lose a major share of their effectivity when mud, moisture, or different supplies accumulate on their surfaces. But when coated with such an lively floor materials, a short magnetic pulse might be used to brush the fabric away.

“Fouling is an enormous drawback on such mirrors,” Varanasi says. “The information reveals a lack of nearly 1 p.c of effectivity per week.”

However at current, even in desert areas, the one approach to counter this fouling is to hose the arrays down, a labor- and water-intensive methodology. The brand new strategy, the researchers say, may result in methods that make the cleansing course of automated and water-free.

“Within the desert setting, mud is current every day,” says co-author Numan Abu-Dheir of the King Fahd College of Petroleum and Minerals (KFUPM) in Saudi Arabia. “The difficulty of mud mainly makes the usage of photo voltaic panels to be much less environment friendly than in North America or Europe. We’d like a approach to scale back the mud accumulation.”

One benefit of the brand new active-surface system is its effectiveness on a variety of floor contaminants: “You need to have the ability to propel mud or liquid, many supplies on surfaces, no matter their properties,” Varanasi says.

MIT postdoc Seyed Mahmoudi, a co-author of the paper, notes that electrical fields can’t penetrate into conductive fluids, resembling organic fluids, so standard methods wouldn’t be capable of manipulate them. However with this method, he says, “electrical conductivity just isn’t necessary.”

As well as, this strategy provides a substantial amount of management over how materials strikes. “Energetic fields — resembling electrical, magnetic, and acoustic fields — have been used to govern supplies,” Khalil says. “However not often have you ever seen the floor itself work together actively with the fabric on it,” he says, which permits a lot larger precision.

Whereas this preliminary demonstration used a magnetic fluid, the workforce says the identical precept might be utilized utilizing different forces to govern the fabric, resembling electrical fields or variations in temperature.

Neelesh Patankar, a professor of mechanical engineering at Northwestern College who was not concerned on this work, says this analysis “introduces a brand new class of strategy for droplet-based microfluidic platforms, which have quite a few functions in quite a lot of fields, together with biotechnology.” He provides, “This work cleverly combines low-hysteresis droplet motion with low-magnetic-field-driven droplet propulsion to realize spectacular capabilities.”

The work was supported by the MIT-KFUPM Heart for Clear Water and Clear Vitality.

Publication: Karim S. Khalil, et al., “Energetic surfaces: Ferrofluid-impregnated surfaces for lively manipulation of droplets,” Appl. Phys. Lett. 105, 041604, 2014;

Picture: MIT Information, Courtesy of the Researchers

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