New Technique ‘Defies’ Laws of Physics

Researchers at Argonne National Laboratory, Illinois, have found a way to apply pressure to make a material expand instead of compress.

Pressure-induced transitions are associated with near two-fold volume expansions. While an increase in volume with pressure is counterintuitive, the resulting new phases contain large fluid-filled pores, such that the combined solid-fluid volume is reduced and the inefficiencies in space filling by the interpenetrated parent phase are eliminated (Argonne National Laboratory)

Pressure-induced transitions are associated with near two-fold volume expansions. While an increase in volume with pressure is counterintuitive, the resulting new phases contain large fluid-filled pores, such that the combined solid-fluid volume is reduced and the inefficiencies in space filling by the interpenetrated parent phase are eliminated (Argonne National Laboratory)

Scientists use framework materials, which have sponge-like holes in their structure, to trap, store and filter materials. The shape of the sponge-like holes makes them selectable for specific molecules, allowing their use as water filters, chemical sensors and compressible storage for carbon dioxide sequestration of hydrogen fuel cells. By tailoring release rates, scientists can adapt these frameworks to deliver drugs and initiate chemical reactions for the production of everything from plastics to foods.

The Argonne researchers put zinc cyanide – a material used in electroplating – in a diamond-anvil cell and applied high pressures of about 9,000 to 18,000 times the pressure of the atmosphere.

By using different fluids around the material as it was squeezed, they were able to create five new phases of material, two of which retained their new porous ability at normal pressure. The type of fluid used determined the shape of the sponge-like pores.

This is the first time that hydrostatic pressure has been able to make dense materials with interpenetrated atomic frameworks into novel porous materials.

“It’s like squeezing a stone and forming a giant sponge,” said Dr Karena Chapman, senior author of a paper describing the findings in the Journal of the American Chemical Society.

“Materials are supposed to become denser and more compact under pressure. We are seeing the exact opposite. The pressure-treated material has half the density of the original state. This is counterintuitive to the laws of physics.”

“The bonds in the material completely rearrange. This just blows my mind.”

“This could not only open up new materials to being porous, but it could also give us access to new structures for selectability and new release rates,” said study co-author Dr Peter Chupas.

The discovery will do more than rewrite the science text books; it could double the variety of porous framework materials available for manufacturing, health care and environmental sustainability.

“By applying pressure, we were able to transform a normally dense, nonporous material into a range of new porous materials that can hold twice as much stuff. This counterintuitive discovery will likely double the amount of available porous framework materials, which will greatly expand their use in pharmaceutical delivery, sequestration, material separation and catalysis,” Dr Chapman said.

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Bibliographic information: Saul H. Lapidus et al. 2013. Exploiting High Pressures to Generate Porosity, Polymorphism, And Lattice Expansion in the Nonporous Molecular Framework Zn(CN)2. J. Am. Chem. Soc., 135 (20), pp. 7621 – 7628; doi: 10.1021/ja4012707