A groundbreaking study from Oxford University, published in Nature Nanotechnology, challenges the long-held belief of Coulomb’s Law, suggesting that like charges can attract each other in solutions like water or alcohol. Contrary to electromagnetic principles, the research reveals that similarly charged particles in solution may exhibit attraction over significant distances, with the effect varying depending on the solvent.
The Department of Chemistry at Oxford discovered that in water, negatively charged particles are drawn together, forming hexagonal clusters, while positively charged particles repel each other. However, the behaviour shifts in alcohol, where positive charges attract to form clusters and negative charges repel.
Utilising bright-field microscopy, the Oxford researchers observed the formation of hexagonal clusters among negatively charged silica microparticles suspended in water. Conversely, positively charged particles did not display such properties in water. By applying interparticle interactions theory, which considers the chemistry of the solvent interface, the team concluded that in water, the attractive force among negatively charged particles outweighs electrostatic repulsion at large separations, facilitating cluster formation. On the other hand, the solvent-driven interaction is repulsive, preventing cluster formation among positively charged particles.
The observed effect was found to be pH-dependent. In solvents like ethanol, with different interface behaviour compared to water, positively charged aminated silica particles formed hexagonal clusters, while negatively charged silica did not.
Professor Madhavi Krishnan, who led the study from the Department of Chemistry at Oxford University, expressed pride in the achievements of both graduate and undergraduate students involved in the research. “I am very proud of my two graduate students, as well as the undergraduates, who have all worked together to move the needle on this fundamental discovery,” Prof. Krishnan remarked.
Sida Wang, the first author of the study from the Department of Chemistry at Oxford University, shared his fascination with the discovery. “I still find it fascinating to see these particles attract, even having seen this a thousand times,” Wang expressed.
The study marks a significant breakthrough in understanding particle interactions in solution and opens new avenues for research in nanotechnology and materials science.
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