New Study Shows Like-Charged Particles Attract or Repel in Solution

You know how like-charged objects repel - and do so regardless of the sign of their electrical charge? Maybe not always, according to new research published in Nature. "We demonstrate experimentally that the solvent plays a hitherto unforeseen but crucial role in interparticle interactions," they write. But more importantly, "interactions in the fluid phase can break charge-reversal symmetry. We show that in aqueous solution, negatively charged particles can attract at long range while positively charged particles repel. [In solvents like alcohols "that exhibit an inversion of the net molecular dipole at an interface"], positively charged particles may attract whereas negatives repel. The observations hold across a wide variety of surface chemistries: from inorganic silica and polymeric particles to polyelectrolyte- and polypeptide-coated surfaces in aqueous solution. A theory of interparticle interactions that invokes solvent structuring at an interface captures the observations. Our study establishes a nanoscopic interfacial mechanism by which solvent molecules may give rise to a strong and long-ranged force in solution, with immediate ramifications for a range of particulate and molecular processes across length scales such as self-assembly, gelation and crystallization, biomolecular condensation, coacervation, and phase segregation. The delicate interplay of interactions between objects in the fluid phase influences the behaviour, organization and properties of systems from nanometric to more macroscopic size and length scales and thus underpins a wealth of natural phenomena... Thanks to long-time Slashdot reader Greymane for sharing the article.

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