Scientists have used magnetic nanoparticles in polymer matrices to replicate the 3D structural reinforcement found naturally in materials such as seashells.
Scientists in Switzerland have used extremely low magnetic fields to align particles within composite polymers, thus reinforcing the structure in three dimensions. Though these materials probably won’t ever be used to hold up buildings, the researchers’ tests demonstrate that they are stronger and more resistant to wear than plain polymers so they could find use as specialized materials, reports Simon Hadlington for Chemistry World.
Teeth, bone, and seashells are a few examples of materials that naturally have 3D reinforcement. Research team leader André Studart at the Swiss Federal Institute of Technology (ETH) in Zurich told Hadlington:
In seashells there are two layers, an inner one consisting of tiny platelets of calcium carbonate that are organised parallel to the shell’s surface; on top is an outer layer of calcium carbonate rods that are aligned perpendicular to the surface. This provides high hardness and wear resistance on the outer surface, as well as an ability to arrest cracks that reach the inner layer.
Replicating nature’s 3D reinforcement strategy within polymer composites has been tricky. The standard treatment involves integrating mesh or fibers, but these 2D reinforcements only provide strength in one plane.
To make their composite, the ETH team first magnetized micrometer-sized aluminum platelets and rods of calcium sulfate hemihydrate by coating them with iron oxide nanoparticles. Hadlington explains the next step:
The platelets or rods were then suspended in a solution of precursors of a range of polymers, including polyurethane, epoxy resins and acrylate. When a low magnetic field was applied, the structures aligned in a specific orientation, becoming locked in place once polymerisation was initiated.
Finally, the researchers established the 3D reinforcement by aligning the particles in each layer of the polymer matrix in different planes. In their tests, the researchers experimented with various combinations of particles, thickness of iron oxide coatings, and strengths of magnetic fields.
Studart told Chemistry World that the magnetic field emitted by a credit card strip is stronger than the one that aligned the particles in their material, which means that the process could be scaled up easily and inexpensively.
Emile Greenhalgh, a composites expert at Imperial College London in the U.K., describes the approach to Hadlington as worth pursuing for specialized materials but not for replacing high-performance structural composites.
Source: “Composites reinforced in 3D,” Chemistry World, 1/12/12
Image by Manfred Heyde via Wikimedia Commons, used under Fair Use: Reporting.
Rachel Petkewich is a freelance science writer and editor. She has worked as a research scientist in the chemical industry and spent eight years as a staff writer and editor at various science journals and magazines, including Chemical & Engineering News.
