Engineered surface treatment developed at MIT can reduce waste and improve efficiency in many processes — ScienceDaily

The slippery coatings the workforce has developed, referred to as liquid-impregnated surfaces, might have quite a few benefits, together with eliminating manufacturing waste that outcomes from materials that sticks to the insides of processing gear. They may additionally improve the standard of merchandise starting from bread to prescribed drugs, and even improve the efficiency of circulation batteries, a quickly growing know-how that might assist to foster renewable power by offering cheap storage for generated electrical energy.

These surfaces are based mostly on ideas initially developed to assist meals, cosmetics, and different viscous liquids slide out of their containers, as devised by Kripa Varanasi, a professor of mechanical engineering at MIT, together with former college students Leonid Rapoport PhD '18 and Brian Solomon PhD '16. The new work is described in the journal ACS Applied Materials and Interfaces.

Like the sooner surfaces they developed, which led to the creation of a derivative firm referred to as LiquiGlide, the brand new surfaces are based mostly on a mixture of a specifically textured surface and a liquid lubricant that coats the surface and stays trapped in place via capillary motion and different intermolecular forces related to such interfaces. The new paper explains the elemental design ideas that can obtain nearly 100 % friction discount for these gel-like fluids.

Needing a squeeze

Such supplies, generally known as yield-stress fluids, together with gels and pastes, are ubiquitous. They can be discovered in shopper merchandise resembling meals, condiments, and cosmetics, and in merchandise in the power and prescribed drugs industries. Unlike different fluids resembling water and oils, these supplies is not going to begin to circulation on their very own, even when their container is turned the wrong way up. Starting the circulation requires an enter of power, resembling squeezing the container.

But that squeezing has its personal results. For instance, bread-making equipment usually contains scrapers that always push the sticky dough away from the edges of its container, however that fixed scraping can end result in over-kneading and a denser loaf. A slippery container that requires no scraping might thus produce better-tasting bread, Varanasi says. By utilizing this method, "beyond getting everything out of the container, you now add higher quality" of the ensuing product.

That is probably not crucial the place bread is worried, nevertheless it can have nice impression on prescribed drugs, he says. The use of mechanical scrapers to propel drug supplies via mixing tanks and pipes can intrude with the effectiveness of the medication, as a result of the shear forces concerned can harm the proteins and different lively compounds in the drug.

By utilizing the brand new coatings, in some circumstances it is attainable to attain a 100 % discount in the drag the fabric experiences -- equal to "infinite slip," Varanasi says.

"Generally speaking surfaces are enablers," says Rapoport. "Superhydrophobic surfaces, for example, enable water to roll easily, but not all fluids can roll. Our surfaces enable fluids to move by whichever way is more preferable for them -- be it rolling or sliding. In addition we found that yield-stress fluids can move on our surfaces without shearing, essentially sliding like solid bodies. This is very important when you want to maintain the integrity of these materials when they are being processed."

Like the sooner model of slippery surfaces Varanasi and his collaborators created, the brand new course of begins by making a surface that's textured at the nanoscale, both by etching a sequence of carefully spaced pillars or partitions on the surface, or mechanically grinding grooves or pits. The ensuing texture is designed to have such tiny options that capillary motion -- the identical course of that enables bushes to attract water as much as their highest branches via tiny openings beneath the bark -- can act to carry a liquid, resembling a lubricating oil, in place on the surface. As a end result, any materials inside a container with this type of lining basically solely comes in contact with the lubricating liquid, and slides proper off as an alternative of sticking to the stable container wall.

The new work described in this paper particulars the ideas the researchers got here up with to allow the optimum collection of surface texturing, lubricating materials, and manufacturing course of for any particular software with its specific mixture of supplies.

Helping batteries to circulation

Another essential software for the brand new coatings is in a quickly growing know-how referred to as circulation batteries. In these batteries, stable electrodes are changed by a slurry of tiny particles suspended in liquid, which has the benefit that the capability of the battery can be elevated at any time just by including larger tanks. But the efficiency of such batteries can be restricted by the circulation charges.

Using the brand new slippery coatings might considerably enhance the general efficiency of such batteries, and Varanasi labored with MIT professors Gareth McKinley and Yet-Ming Chiang on growing such a system led by Solomon and Xinwei Chen, a former postdoc in Chiang's lab.

These coatings might resolve a conundrum that circulation battery designers have confronted, as a result of they wanted so as to add carbon to the slurry materials to improve its electrical conductivity, however the carbon additionally made the slurry a lot thicker and interfered with its motion, resulting in "a flow battery that couldn't flow," Varanasi says.

"Previously flow batteries had a trade-off in that as you add more carbon particles the slurry becomes more conductive, but it also becomes thicker and much more challenging to flow," says Solomon. "Using slippery surfaces lets us have the best of both worlds by allowing flow of thick, yield-stress slurries."

The improved system allowed using a circulation electrode formulation that resulted in a fourfold enhance in capability and an 86 % financial savings in mechanical energy, in contrast with using conventional surfaces. These outcomes have been described just lately in the journal ACS Applied Energy Materials.

"Apart from fabricating a flow battery device which incorporates the slippery surfaces, we also laid out design criteria for their electrochemical, chemical, and thermodynamic stability," explains Solomon. "Engineering surfaces for a flow battery opens up an entirely new branch of applications that can help meet future energy storage demand."

The analysis was supported by the Joint Center for Energy Storage Research, an Energy Research Hub funded by the U.S. Department of Energy, and by the Martin Family Society of Fellows for Sustainability.