MIT Found a New Way to Assemble Nanoparticle Crystals: Let the Connectors Bend.

To build a crystal from nanoparticles, researchers have long tried to control exactly where each tiny building block connects to its neighbors. That usually meant shaping the particles carefully or using connectors that point in specific directions. A study published on November 2, 2026 in Nature Materials offers a different design rule: make some of those molecular connectors flexible enough to rearrange themselves during assembly. The resulting particles can form ordered structures with fewer neighbors than their shape alone would predict.

The peer-reviewed study, led by a team including MIT researchers, calls this mechanism spontaneous valency. The result is supported by both laboratory measurements and computational simulations.

Why flexibility changes a crystal's geometry

A nanoparticle superlattice is a repeated arrangement of nanoscale particles. Different repeating arrangements can produce different optical, electrical, chemical or mechanical behavior. Conventional attractive forces tend to favor densely packed structures, where each particle contacts as many neighbors as possible. For designer materials, that can be a limitation: a more open lattice may expose useful surfaces or create different light-interaction patterns.

Nanoparticles can be coated in molecules called ligands, which help determine how the particles interact. In the new experiments, ligands contain flexible polymer chains with charged ends. Opposite charges attract, and the chains bend or reorganize as two particles approach. Rather than a fixed geometry instructing each bond, the arrangement of the ligand layer itself makes some positions more favorable than others.

The researchers use the term valency for the effective number of neighboring particles to which one building block connects. In atomic chemistry, valency is associated with characteristic bonding. Here the idea is an emergent, collective property of soft molecular coatings rather than a fixed count carved into the nanoparticle surface. As ligand deformability increases, the study reports lower lattice coordination numbers and less-dense structures.

MIT's November 2 explanation describes the counterintuitive choice: increasing connector flexibility can create controlled assembly, rather than destroying it.

What the team actually changed

The experimental team varied the relative sizes of nanoparticles and the lengths of ligand chains. This changed how many neighbors could bind and produced lattice motifs not previously achieved with the same design approach. Measurements of the assembled structures were compared with simulations to test whether a model of flexible, electrostatically interacting ligands explains the observed symmetry changes.