Multifunctional surface flips from sticky to slippery on demand
Surfaces are usually designed to have a certain topography, and you'll usually have to choose if they're sticky or slippery depending on what you need. But now, Harvard scientists have led an international team to develop a new surface that can reconfigure its shape, stickiness or slipperiness on demand, through the application of a magnetic field.
The team calls its creation a Ferrofluid-containing Liquid-infused Porous Surface (FLIPS), and as the extremely forced acronym suggests, it's designed to "flip" between different states. It does so through the interactions of its two composite parts – a liquid containing magnetic particles and a solid substrate with a tiny, textured structure.
When left to its own devices, the magnetic liquid (known as a ferrofluid) spreads across the top of the substrate, forming a smooth, slippery surface. But when a magnetic field is applied, the ferrofluid will cling closer to the shape beneath it, changing the properties of the material at the surface. For example, it could become adhesive or provide friction in only one direction.
That way, FLIPS can be tuned for different purposes by changing the geometry of the substrate, the type of ferrofluid used, and the strength, position and placement of the magnetic field. It works at different scales too, creating changes at the centimeter, millimeter or micrometer levels.
The team says this versatility can be put to work in a wide range of applications; the surface could become an adhesive that can be switched on and off at will; pipes coated with the stuff could continuously pump liquids; bacteria and particles could be directed in very specific ways for micro-scale manufacturing; droplets of different liquids could be mixed at precise times for chemical reactions; or it could make surfaces self-cleaning against bacterial biofilms.
"Each of these applications can be further extended," says Wendong Wang, first author of a paper describing the new surface. "Our results suggest that FLIPS allows much more diverse combinations of functions and capabilities than surfaces that have only a simple, single-scale topographical response. This could be a platform for a lot of future technologies."
The research was published in the journal Nature, and the team demonstrates the different properties in the video below.