The interaction between charged objects in solution is generally expected to recapitulate two central principles of electromagnetics: (1) like-charged objects repel, and (2) they do so regardless of the sign of their electrical charge. Here we demonstrate experimentally that the solvent plays a hitherto unforeseen but crucial role in interparticle interactions, and importantly, that 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 that exhibit an inversion of the net molecular dipole at an interface, such as alcohols, we find that the converse can be true: 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.

溶液中带电物体之间的相互作用通常被认为能够概括电磁学的两个核心原理：（1）同性带电物体相互排斥，（2）无论其电荷的符号如何，它们都会相互排斥。在这里，我们通过实验证明溶剂在颗粒间相互作用中发挥着迄今为止不可预见但至关重要的作用，而且重要的是，流体相中的相互作用可以打破电荷反转对称性。我们证明，在水溶液中，带负电的颗粒可以在远距离吸引，而带正电的颗粒则相互排斥。在界面处表现出净分子偶极子反转的溶剂（例如醇）中，我们发现反之亦然：带正电的粒子可能会吸引，而带负电的粒子可能会相互排斥。这些观察结果适用于各种表面化学：从无机二氧化硅和聚合物颗粒到水溶液中的聚电解质和多肽涂层表面。粒子间相互作用理论在界面处调用溶剂结构来捕获观察结果。我们的研究建立了一种纳米级界面机制，溶剂分子可以通过该机制在溶液中产生强大的远程力，对一系列跨长度尺度的颗粒和分子过程产生直接影响，例如自组装、凝胶化和结晶、生物分子凝结、凝聚和相分离。