- Researchers develop a cutting-edge way to create arrays of nanofibers.
- These nanoscale fibers could make new materials with incredible capabilities.
- The new method was inspired by water-repelling lotus leaves and gravity-defying gecko feet.
Surfaces made of arrays of fibers are ubiquitous in nature. They can provide a variety of functions, for example, thermal insulation (polar bear fur), reversible adhesion (gecko foot), extreme wetting characteristics (lotus leaf), sensing (hair cells) and enhanced mass transport (microtubules).
Lotus leaves are coated with arrays of waxy tubules to repel water. Polar bear hairs are formed in a way so that no heat can escape them. And tiny hairs on the bottoms of gecko feet get so close to other surfaces that they overcome the force of gravity (due to the force of atomic attraction between hairs and surface).
Recreating these features in synthetic material requires multi-scale engineering of composition, fiber morphology, and precise control over higher-order arrangements of fibers into arrays.
Recently, researchers at the University of Wisconsin-Madison and the University of Michigan serendipitously discovered a powerful technique for creating arrays of nanoscale fibers that could make new materials with incredible capabilities.
The researchers made special nanofibers by knitting clockwise and anti-clockwise twisted fibers together. These fibers were bonded more tightly compared to an array of two straight fibers.
The resulting nanofibers were able to repel water just like lotus leaves. They experimented with optical characteristics and made a structure that glowed. Also, the team believes that each fiber structure can be designed to work like polar bear fur.
The Accidental Discovery
Making molecular carpets wasn’t the actual plan. The researchers were trying to create sensors capable of detecting individual molecules. They put polymers — substances made of a large number of molecules all strung together to form incredibly long chains — on top of liquid crystals.
These are the same liquid crystals that are used in electronic displays like computer screens and televisions. In usual experiments, the team evaporates each link of the chain and coaxes it to condense onto surfaces.
Two arrays of nanofibers curving in opposite directions, each templated with a liquid crystal | Credit: Michigan Engineering
However, this thin layer of polymer sometimes did not work as expected. Rather than staying at the top of the fluid, the links slipped through the liquid crystal and stuck together with one another on the glass slide.
The shape of the fibers was then guided by the liquid crystal, evolving from the bottom and eventually forming nanoscale fiber carpets.
Researchers were quite surprised with the results because despite being disordered fluids, liquid crystal precisely guided the formation of nanofibers with well-defined diameters and lengths.
They did not only create straight strands, but also curved fibers, such as microscopic staircases and bananas, by altering the internal ordering of the liquid crystal.
Overall, this method enables scalable fabrication of arrays of nanofibers with programmable chemistries, shape, and long-range lateral arrangements. It adds a lot of complexity to the way how researchers can make surfaces in three dimensions.