Neutron research shows solvent microstructure influences nanomaterials

19 March 2026

Nanoparticles have become an integral part of our modern everyday lives: they are found in medicines, catalysts, paints, and high-tech materials. But although they are extremely small, they have often been described using the classical chemical view of the solvent as a continuum medium or an “additive” factor. A new study now demonstrates that these simplifications are reaching their limits—and that solvents play a much more active role at the nanoscale than previously predicted.

An international research team involving Dr. Aurel Radulescu from the Jülich Centre for Neutron Science (JCNS) has quantitatively measured for the first time how solvent molecules organize themselves on the surface of nanoparticles. The surprising result: in certain mixtures, tiny clusters of only a few solvent molecules form, which specifically “attack” the surface of the particles and even change their shape.

Solvents are not a uniform liquid

In the classical view of chemistry, solvents are considered a kind of uniform background. Properties such as polarity or dielectric constant are averaged, and in mixtures it is assumed that the effects simply add up. This works well for large systems in bulk or on a micrometer scale – but apparently not for nanoparticles.

The reason for this is that on a surface measuring just a few nanometers, each molecule only “sees” a handful of neighbours. Under these conditions, local structures arise: small, short-lived clusters of solvent molecules, only about one nanometer in size. Researchers have now been able to experimentally verify and quantify the existence of these clusters.

Neutrons make the invisible visible

This was achieved by a combination of small-angle neutron scattering (SANS) at the Jülich outstation at the Heinz Maier-Leibnitz-Zentrum (MLZ) in Garching and the Institute Laue-Langevin in Grenoble, together with elaborate computer calculations. “This enabled us not only to characterize the structure of the nanoparticles, but also to resolve with molecular-level precision, how a solvent behaves at the particles’ organic shell and drives the particles shape deformation”, explains Dr. Radulescu, instrument manager of the neutron small-angle diffractometer KWS-2, which was used for the study and is operated by Forschungszentrum Jülich at the MLZ. “Using neutron contrast variation techniques alone, it is not possible to accurately distinguish between competing spherical and elliptical structural models, but we have demonstrated that this can be achieved reliably in combination with Monte Carlo calculations”.

The objects of investigation were gold nanoparticles covered with a thin layer of organic molecules. Depending on the mixture of two solvents used, this shell changed significantly—not uniformly, but in a highly nonlinear manner.

From perfect tiny spheres to elongated particles

Particularly remarkable was that, on mixing two solvents at the right ratio, the nanoparticles lost their spherical symmetry and became slightly elongated. Changing the proportion of the mixing ratio brought the spherical form back.

The effect occurred precisely at the so-called azeotropic point—i.e. compositions in which the two solvents behave like a single pure component, which is where the formation of tiny solvent clusters was most pronounced.

Shape change, increased solvent penetration, and maximum cluster formation always occurred together. This enabled the researchers to demonstrate directly for the first time that the microscopic structure of a solvent controls the geometry of nanoparticles.

A universal mechanism

The effect is not limited to a single system. It was observed:

• in surface organic molecules of different lengths,
• in very different solvent pairs,
• even in solvent mixtures lacking hydrogen bonding.

This suggests a general physical mechanism: non-ideal mixing creates local solvent structures that lead to symmetry breaking on curved surfaces.

Why this is important

The results challenge fundamental assumptions in colloid and nanochemistry. At the nanoscale, solvents can no longer be treated as a passive environment—they become active structure-determining agents.

This opens up new possibilities:

• The shape and stability of nanoparticles could be controlled specifically by choosing the right solvent.
• Self-organization and aggregation could be controlled more precisely.
• The findings are also relevant for polymers, biomolecules, and hybrid materials.

In short, anyone who wants to design nanomaterials in the future will not only have to consider the particles themselves, but also the fine, often invisible structure of the solvent in which they float.

Original publications:

Quantifying Å-Scale Non-Additive Solvation at Nanoparticle Interfaces; Xindi Liu et al., Angewandte Chemie, Volume 64, Issue 48, November 24, 2025, e202516308; https://doi.org/10.1002/anie.202516308

Small-angle neutron scattering differentiates molecular-level structural models of nanoparticle interfaces; Yujie Wu et al., Nanoscale, 2025,17, 3798-3808; https://doi.org/10.1039/D4NR04365K