MIT breakthrough could transform how scientists design materials at the nanoscale

Making molecular connectors bendier might sound like a recipe for a disorganized material. Instead, extremely flexible connectors helped tiny particles form ordered networks with fewer neighbors. The finding challenges a common assumption in nanoparticle assembly: that controlling structure requires connectors locked into particular directions. Here, the connectors helped establish those directions as assembly unfolded.

A team including researchers at the Massachusetts Institute of Technology demonstrated the approach using nanoparticles coated with flexible polymer chains. Electrically charged tips drew the chains together, while their ability to deform influenced the resulting arrangements. The study, published in Nature Materials, combines experiments with simulations to explain this unexpected route to structural control.

The work addresses a stubborn problem in making nanoparticle-based materials. Individual particles can have useful properties, but assembling them into larger structures adds another design challenge. Their arrangement matters alongside their composition. Controlling that arrangement could expand the kinds of materials scientists can build from the same starting particles.

A material's structure helps determine what it does. Nanoparticles offer building blocks whose sizes, shapes and compositions can be adjusted for different purposes. They already feature in research and applications involving drug delivery, energy storage, computing and sensing. Turning those building blocks into an organized network, however, requires control over their interactions.

“That means if you know what your building blocks are and how they’re arranged, you can explain what properties materials have,” said Rob Macfarlane. He is the Richard P. Simmons Professor in Metallurgy in MIT's Department of Materials Science and Engineering. “Controlling that is how you make materials that have new properties.”

One obstacle is the tendency of attracting particles to pack densely. Such arrangements provide many neighboring contacts, but they restrict the available architectures. Scientists call repeating, ordered nanoparticle arrangements superlattices. Making a more open superlattice requires some way to limit how many neighbors each particle connects with.

Earlier strategies have included changing particle shapes or making selected surface regions sticky. Those features can guide particles into particular arrangements. But producing them can require elaborate synthesis tailored to a specific material, size or condition. A successful laboratory recipe therefore does not automatically become a broadly usable manufacturing method.

The team focused on ligands, molecules attached to nanoparticle surfaces that influence how particles interact. In many directional assembly strategies, these connectors must preserve particular orientations. The researchers instead explored the opposite extreme. They wanted connectors flexible enough to reorganize as neighboring particles approached one another.

“We thought, ‘Let’s do the exact opposite: make the bonds so flexible it doesn’t matter what direction they’re initially pointing.’ The ligands can then reorganize as the particles come together, and that reorganization itself limits how many neighbors each particle can bind,” Macfarlane said. That shifts part of the design problem from fixed geometry to molecular behavior. The connections emerge through assembly itself.

The system uses flexible polymer ligands with electrically charged tips. Some tips carry positive charges, while others carry negative charges. Opposite charges attract, encouraging the chains to bend toward compatible partners. Their flexibility allows the connecting molecules to respond to the surrounding particles rather than retain a predetermined direction.

This is a form of self-assembly, in which interactions among components produce an organized structure. The particles are not individually placed into position. Instead, their surface chemistry shapes how they come together. The important question is which arrangements those interactions favor when the connectors can deform substantially.

As the particles assemble, their flexible outer coatings can reorganize along the interfaces between them. This produces an effective valency, meaning a preferred number of neighboring connections. The number need not be specified through the particle's shape or a fixed pattern of sticky patches. It can arise from the behavior of the coating.

The researchers found that greater ligand deformability could lower the lattice coordination number, another term for the number of neighboring particles. That matters because fewer neighbors can produce less densely packed structures. The finding links a molecular property, flexibility, to the architecture of an entire particle network. It supplies another variable for designing that architecture. Researchers can therefore consider the polymer coating alongside the particle core when deciding which network to pursue.

In experiments led by MIT doctoral candidate Nicholas Sbalbi, the team changed nanoparticle sizes and ligand-chain lengths. Those adjustments altered how the particles connected and the structures they formed. The researchers also assembled crystal structures described in the announcement as previously unseen. The central result is structural control, rather than a demonstrated improvement in a finished device.

“Without having to predesign where the particles connect or what their shapes are, we can control the number of bonds each particle has,” Macfarlane said. “The amount of flexibility of the polymer dictates how many bonds it has. It allows us to lower the number of bonds each particle has and make lattices we have never seen before.”

The project brought experimental and computational work together. Sbalbi, MIT undergraduate Hana Shinzawa and Matthew Ye designed and performed experiments and analyzed experimental data. Stephen Kronenberger, a doctoral student at the University of Delaware, conducted and analyzed molecular dynamics simulations. These calculations examined how the molecular components behaved during assembly.

Macfarlane supervised the experimental work, while Arthi Jayaraman supervised the computational research. Jayaraman is a former University of Delaware professor whose affiliation on the paper is IBM France. Combining the two approaches helped establish ligand flexibility as a design parameter. The result does not mean every flexible coating will produce any desired structure.

The distinction is important for interpreting the advance. The team demonstrated a route to structures with lower coordination, packing density and symmetry than hard-sphere packing would predict. That expands the available design choices. It does not establish that rigid connectors or shaped particles have become unnecessary across all nanoparticle systems.

The researchers see potential applications in photonics, which involves controlling light, and chemical catalysis, which accelerates reactions. Medicine and agriculture are other proposed directions. Those possibilities depend on matching a structure to a particular task. Demonstrating an assembly method is an earlier step than demonstrating performance in those settings.

Nanoparticles and polymers already support diverse approaches to drug delivery. This study adds a different kind of control over how particles organize. Whether that control translates into a useful medical material remains to be tested. The same distinction applies to the other proposed applications.

For Macfarlane, a longer-term goal is separating the choice of particle from the choice of assembled structure. Researchers would then have more freedom to select building blocks for their useful properties. Flexible connectors offer another route toward that goal. The next practical challenge is establishing which less dense arrangements deliver a measurable advantage for a specific application.

These resources place the findings alongside recent advances and foundational approaches to organizing nanoparticles.

Assembly of open superlattices from valence-free nanoparticles
This research highlight describes a separate approach to open structures using charged, polymer-coated nanoparticles. (Advanced Photon Source, June 2026)

Nanocrystal Assemblies: Current Advances and Open Problems
A broad review examines assembly strategies, structural prediction and obstacles to making functional nanoparticle materials. (ACS Nano, May 2024)

Nanoparticle Assembly as a Materials Development Tool
This perspective explains how particle composition, size and surface chemistry influence materials development. (Journal of the American Chemical Society, February 2022)

Nanoparticle Superlattices: The Roles of Soft Ligands
This review provides background on how soft surface molecules influence nanoparticle interactions and ordered structures. (Advanced Science, September 2017)

Diamond family of nanoparticle superlattices
This foundational study demonstrates diamond-related nanoparticle lattices assembled through DNA-based design. (Science, February 2016)

Research findings are available online in the journal Nature Materials.

The original story "MIT breakthrough could transform how scientists design materials at the nanoscale" is published in The Brighter Side of News.

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