Prof. Rob Macfarlane & team developed a new approach to nanoparticle assembly, using highly flexible connector molecules to control how nanoparticles link together and create materials for photonics, chemical catalysis, medicine, & more. @MITEngineering.
Building Better Microscopic Legos: The Power of a “Squishy” Coating.
Consider building a complex, open-frame structure out of microscopic Lego bricks. Normally, to make pieces connect in specific, limited directions, the bricks themselves need to have special shapes—like distinct bumps, holes, or flat sides.
In nanotechnology, scientists build advanced materials by assembling tiny particles (nanoparticles) into organized structures called superlattices. These particles are typically coated in a layer of sticky molecules (called ligands). However, because these coatings are usually rigid, the particles tend to just clump together into dense, tightly packed clusters, maximizing the number of connections. For a long time, scientists believed that if they wanted to build more complex, open, or directional structures, they had to engineer the nanoparticles themselves to be asymmetrical or specially patterned.
But researchers have now discovered a clever workaround: you can use perfectly round, uniform nanoparticles and still get them to form complex, open structures. The secret lies in making their sticky outer coating flexible.
Think of this flexible coating like a squishy, adaptive layer of Velcro. When the nanoparticles come close to each other, this soft outer layer deforms and shifts. Instead of wrapping evenly around the particle, the molecules reconfigure themselves to line up only at the points where the particles touch. This spontaneous shifting creates natural, specific “bonding spots” (a concept scientists call *valency•, dictating exactly how many neighbors a particle can connect to and in what direction.
Through a combination of laboratory experiments and computer simulations, the researchers proved that by simply tuning how flexible this outer coating is, they can control the final structure. More flexibility leads to fewer connections per particle, allowing the assembly of intricate, less densely packed materials with unique symmetries that were previously thought impossible for uniform, round particles.
