June 3, 2026• Physics 19, s70 Size-dependent electrostatic barriers place an upper limit on droplet merging efficiency. F. Chen et al. [1]: adapted by APS/Carin Cain F. Chen et al. [1]: adapted by APS/Carin Cain × A well-shaken mixture of oil and vinegar will separate as the oil droplets eventually coalesce. Droplet growth, or coarsening, usually evolves according to standard rules. But puzzling exceptions persist.