Research Highlights : Materials , Engineering
Thin membranes tough it out
11 August 2006 (Volume 1 Issue 8)
Molecular sheet could find uses in filtration and fuel cells
Figures 1a and 1b: These optical micrographs show how the nanomembrane can be sucked through the tiny tip of a pipette.enlarge image
A tough, flexible membrane just a few molecules thick has been grown to the size of a large postcard. Such thin sheets have never been grown this big before, and could find a range of uses in nanotechnology, the science of engineering at the molecular scale.
Permeable membranes can be used as filters, for example, while their elastic properties make them useful as sensors, rather like the tight skin of an eardrum.
Previous attempts to make such thin films have mostly been unsuccessful because they are simply too fragile. The thinnest membranes that can cover a significant area are generally several hundred nanometres (billionths of a metre) thick.
But Toyoki Kunitake and colleagues at RIKEN’s Frontier Research System in Wako have now developed a tough membrane just 35 nanometres thick, with an area of 16 cm2.
The membrane is made from a mixture of zirconium oxide and various carbon-based polymers. Combining these ingredients in just the right proportions produces a sheet that is surprisingly strong yet incredibly thin, they report in the journal Nature Materials1. "And we can make much bigger sheets, if a larger apparatus is available," says Kunitake. The team found that when the membrane was floating in a pool of alcohol, it was flexible enough to be sucked into the tip of a tiny pipette, folding up like a well-packed parachute as it passed through a hole some 30,000 times smaller than the sheet itself (Fig. 1).
Figure 2: The thin film, supported by a wire loop, does not become brittle even when it dries out.enlarge image
One previous problem with thin films is that they usually become brittle when allowed to stand in air rather than in a protective bath of solvent. But the team’s membrane retained its strength for several months even when it was hung out to dry (Fig. 2).
In a final feat of strength, the dry film was placed over the end of a glass tube and used to support a column of alcohol that weighed about 70,000 times more than the film itself. The membrane was slightly permeable, allowing one drop of the liquid to seep through every ten seconds or so.
The scientists say this is a good sign that their sheet could be useful as a separation membrane, allowing certain molecules through while keeping others back. This process is also crucial to developing more efficient fuel cells, an environmentally friendly source of electricity that relies on the steady flow of charged ions from one chamber to another.
- Vendamme, R., Onoue, S-Y., Nakao, A. & Kunitake, T. Robust free-standing nanomembranes of organic/inorganic interpenetrating networks. Nature Materials 5, 494–501 (2006). |article|