Cellulose may have been around for millions of years, but that doesn't mean it can't teach a modern substance like aerogels a thing or two. A group of researchers have found a way to use cellulose to make a new type of aerogel that can be made flexible and absorbent like a sponge, or crushed into a sheet of "magnetic nanopaper." The aerogel's creators think both materials could find use in microfluidic devices.

By now, aerogels are sort of old news in the materials science community. Invented in 1931, the solids are famous for being light like styrofoam, but also highly porous and extremely rigid, capable of bearing weights many times their own. Although current forms have many uses, a group of scientists decided that overcoming their characteristic stiffness could open up a whole new range of uses.

When they looked for a material to use to circumvent the stiffness, the authors decided to try a type of cellulose. Cellulose, better known as "plants, mostly," is normally used to make products like paper and cardboard, but some forms of cellulose can also be quite strong—one type is thought to be three-quarters the strength of steel.

One of the best methods to make aerogel out of cellulose is to freeze-dry it, removing all moisture and leaving nothing but a web of pure, solid fibers. The gel is highly porous and mostly air at this point, and yet can still sustain a lot of weight.

Before they freeze dried the cellulose, the researchers first soaked it in a solution of two metal compounds, iron sulfate and cobalt chloride. While the cellulose soaked, tiny nanoparticles of the metals would stick to the cellulose and remain even after drying, so it could be used as a magnet if desired.

Once the cellulose was freeze dried into an aerogel, the researchers found it was capable of two different applications. One involved crushing most of the air out of it, resulting in a small, flat piece of magnetic "nanopaper" that could support four hundred thousand pounds per square inch.

But as a regular aerogel, its properties were still highly unusual: the aerogel was flexible and could bend in half and twist easily. Normally aerogels are brittle and fracture under too much force, but the cellulose version could stand twice as much strain as a regular aerogel.

The scientists found that they could also use the flexible aerogel as a tiny sponge. Because its volume was almost 99 percent air, it could absorb water and then be wrung out, while still retaining its shape and magnetic properties. A 60 milligram patch of aerogel could hold about a gram of water—not magical, but it does best the Sham-Wow.

So, has the sponge just been made over as magnetic and highly absorbent? In a way, yes. The very fine structure of cellulose aerogel will allow it to be used in tiny pieces while retaining their characteristics—very stiff and magnetic, or magnetic, flexible, and absorbent—depending on the properties needed.

The authors speculate that their aerogel could find wide use in materials science, as its components, especially the cellulose, come pretty cheap. In the future, it is likely to play the role of a tiny actuator, or appear in microfluidics devices used in fuel cells and for studying the physics of cells.

Nature Nanotechnology, 2010. DOI: 10.1038/nnano.2010.155 (About DOIs).

Listing image by NASA JPL