Bubbles with great potential
What do mattresses, metallic car bodies and chocolate mousse have in common? They can all be made from foam. But what exactly makes this bubble-filled material a product of the future?
It is not easy for Dr. Björn Braunschweig to relax at the end of the day: Even when he tries to enjoy an after-work beer, the researcher from the Cluster of Excellence Engineering of Advanced Materials at the Friedrich-Alexander University (FAU) in Erlangen-Nuremberg, Germany, can’t help but notice the foam at the top of his glass. Why does the local beer from Bavaria have larger bubbles that pop faster than the Guinness® on the next table? “The head on the Irish stout is much more stable because the nitrogen gas used in the carbonation process is less soluble in liquid than the carbon dioxide used for draft German beer,” Braunschweig explains. The 30-something scientist knows a thing or two about foam: In 2014, he received a €1.5 million starting grant for up-and-coming research leaders from the European Research Council for a five-year project to conduct basic research on foams.
Fabulously functional foams
It might seem odd that funding is being channeled into research on foams, of all things, but foam is a very versatile material with a bright future. Layers of Styrodur®, for example, are not only used for insulation, they also reduce the stresses that earthquakes put on buildings, thus giving planners the confidence they need to build in seismically active areas. And joggers need to use less energy when they wear running shoes made with foam beads from BASF because the shoe’s dynamic sole springs back into its original shape immediately after impact. Even as we sleep we can reap the benefits of polyurethane foams because they provide the same high elasticity in mattresses and pillows that was previously only possible with latex, and at the same time they are breathable and long-lasting. “Foams are a booming market,” says Braunschweig. “The air bubbles make the material very light and foams have the huge advantage of extreme plasticity.” In lightweight vehicle construction, foams ensure an optimal balance between robustness and weight. At first glance, a vehicle body made of metallic foam seems just as hard as a traditional one. But if there is a crash, the foam body doesn’t break and split. Instead, it undergoes plastic deformation and – similarly to an airbag – can absorb the impact. To create foams with particular properties, researchers will need to understand every aspect of the foam, from the smallest molecules to the bubbles themselves. The interface – the place where the gas and liquid or the gas and the solid meet in the individual bubbles – is especially important. Which molecular components stabilize this surface? What interactions take place with the molecules there?
The better researchers can answer these questions, the closer they will get to achieving their goal of creating a “molecular toolbox” that can control and predict the properties of foams. “Intelligent foams” demonstrate what the future may hold. These foams can change their properties in response to external stimuli such as light. Braunschweig believes this could play an important role in self-healing foams whose moveable molecules on the bubble’s surface enable the bubble to expand under negative pressure and temporarily close any “injured” cells in the foam structure. Intelligent foams could also be beneficial for the recycling of insulation materials: “When a foam is no longer needed, it could simply be collapsed. The remaining material would have just one-thousandth of its original volume – and it would make it easier to access the chemical components.”
Whipping up something tasty
The food industry, on the other hand, is interested in completely different properties of foam. “It wants to use foams to stabilize quality until the best-before date,” says the Erlangenbased researcher. The industry is also very interested in foams because they have a more intense flavor than traditional foods. The bubbles in foams give them a larger surface area, so they can give off more aromas in a shorter time. And foams appeal to healthy eaters since they are usually lightweights when it comes to calories, too.