A team of researchers from MIT has developed liquid-impregnated surfaces, slippery coatings that could have several advantages such as eliminating production waste that results from material that sticks to the insides of processing equipment. They also have the capacity of improving the quality of products ranging from bread to pharmaceuticals, and even improve the efficiency of how batteries, a rapidly developing technology that could help foster renewable energy by providing inexpensive storage for generated electricity.
The primary basis for these surfaces is on the principles initially developed to help foods, cosmetics, and other viscous liquids slide out of their containers, as devised by Kripa Varanasi, a professor of mechanical engineering at MIT and other colleagues.
The team has earlier developed surfaces that led to the creation of a spinoff company called LiquiGlide. The new surfaces are based on a combination of a specially textured surface and a liquid lubricant that coats the surface and remains trapped in place through capillary action and other intermolecular forces connected with such interfaces. In the new paper, it gave a complete explanation of the fundamental design principles that can achieve almost 100 percent friction reduction for these gel-like fluids.
Materials like gels and pastes are yield-stress fluids, and they are ubiquitous. It is easy to find them in consumer products like food, condiments, and cosmetics, and in products in the energy and pharmaceutical industries.
Similar to other fluids like water and oils, these materials will not start to flow on their own, even when their container is turned upside down. To start the flowing process, one will require an input of energy such as squeezing the container.
Like the earlier version of slippery surface Varanasi and colleagues created, the new process starts by making a surface that is textured at the nanoscale, either by etching a series of strictly distanced pillars or walls on the surface or automatically grinding grooves or pits.
They designed the resultant texture to have such small characteristics that capillary action, the same process that allows trees to draw water up to their highest branches through tiny openings beneath the bark, can act to hold a liquid like lubricating oil, in place on the surface. The result is any material inside a container with this significantly only comes in contact with the lubricating liquid and slides right off instead of sticking to the solid container wall.
Flow batteries, a rapidly developing technology, is another essential application for the new coatings. A slurry of tiny particles replaced solid electrodes of these batteries, which has the advantage that the capacity of the battery can be increased at any time by merely adding bigger tanks. But the flow rates can limit the efficiency of such batteries.
