Nuthalapati, KarthikKarthikNuthalapatiSeemann, RalfRalfSeemannYU-JANE SHENGTsao, Heng-KwongHeng-KwongTsao2025-06-172025-06-172025-05-15https://www.scopus.com/record/display.uri?eid=2-s2.0-105003218376&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/730150This study demonstrates the long-range attractions of self-propelled droplets on polymethyl methacrylate (PMMA) and glass surfaces. These self-propelled droplets are composed of a mixture of N-methylformamide (NMF) or N,N-dimethylformamide (DMF) with either Brij-30 or Pluronic F-127 surfactants. The pure NMF liquid exhibits total wetting, while the pure Brij-30 liquid displays partial wetting on both PMMA and glass. The antagonistic wetting behavior of these mixtures on the PMMA substrate is systematically investigated, leading to the identification of four distinct regimes in the wetting phase diagram of contact angle versus composition. An isolated Brij-laden NMF droplet can exhibit random movement. When multiple droplets are placed at equal intervals on a linear runway with hydrophobic sides, they move toward each other and coalesce, indicating long-range attraction. When arranged in square or hexagonal patterns, neighboring self-propelled droplets gradually attract, coalesce, and eventually merge into a single large droplet. This intriguing finding is attributed to Marangoni stress, which is linked to the slow interfacial relaxation of surface tension in antagonistic mixtures. The long-range attraction between droplets is likely due to the interaction of invisible precursor films surrounding the moving droplets, a phenomenon observed in antagonistic liquids.Antagonistic liquidLong-range attractionMarangoni stressPrecursor filmSelf-propelled droplet[SDGs]SDG6journal article10.1016/j.surfin.2025.106532