Unlike human relationships, particle physics is strict about “like repels, like attracts like.” Just as the same poles of any two magnets resist touching each other, so negative and positive charges have a universal aversion to their own company. But chemists at Oxford University have discovered a fairy tale in a test tube that shows love will always find a way. Even between particles with the same charge.

“Even though I’ve seen it thousands of times, I still find it fascinating to see how these particles are attracted,” says Sida Wang, lead author of the study.

If you suspend several electrons in a complete vacuum, they become electromagnetic daggers and repel each other with a force described by Coulomb’s law. Similarly, protons in space will repel each other due to their common positive charge.

On the other hand, mix them with particles dominated by different charges and watch fireworks. Literally, chemistry wouldn’t be the same if Coulomb’s law didn’t drive soap operas of atomic love triangles.

To simplify, chemists assume that this law holds for both charged particles floating in solution and the same particles in a vacuum. Wang and his team considered the possibility that the rules might not be so simple when it comes to solvers.

In a series of experiments with silica particles in different types of solutions, researchers measured factors such as the acidity and molecular structure of the solvent to determine the strength of the particles’ interactions. They also calculated the density distribution of the particles using an optical microscope.

Based on their observations, it was clear that negatively charged silica particles in water-based solutions do not repel each other as they do in a perfect vacuum. They actually came together. A possible explanation can be found in the study of the pH of the solution affecting the strength of attraction as it moves from a relatively acidic 4 to a highly basic 10.

Surprisingly, positively charged silica particles have never behaved this way, at least in aqueous solutions. However, further experiments using alcohol as a solvent provided an excellent opportunity for the positively charged particles to approach each other. These newly discovered gravitational forces were observed over long distances and balanced by the expected repulsion at shorter distances.

Although the interactions between particles and the solvent are complex, it is clear that they are important enough to overcome the constant Coulomb forces that normally tear apart particles dominated by the same charge. In what the researchers call the “electrosolvation force,” the structure of the solution and its charged components interact with the surface of the suspended particles to create a net gravitational force, pulling the silica into the clusters despite their repulsion. .

The findings could have significant implications in almost any field of science where the movement of charged particles in solution is important, potentially contributing to advances in everything from pharmaceutical development to understanding diseases and developing new types of nanotechnology.

“Similarly charged molecules in solution can actually experience a counterintuitive, strong and long-lasting attraction even under physiological conditions,” Wang and colleagues conclude.