Abstract: To clarify the interaction mechanism of polar collectors at the flotation interface and overcome the technical bottleneck where collector design for coal slime flotation relies heavily on empirical experience and lacks rational guidance, a multi-scale force measurement system spanning the micro-Newton to nano-Newton range was constructed. This system utilized an attachment-detachment force measurement system and Atomic Force Microscopy (AFM) with the oil droplet probe technique. Using bitumen coatings as coal models, three types of coal surfaces—strongly hydrophobic, moderately hydrophobic, and weakly hydrophobic—were prepared. Non-polar n-octane and polar n-octanol were selected as collectors. The study systematically tested and compared the macroscopic attachment-detachment behavior at the coal-bubble interface, the microscopic adhesion characteristics at the oil-coal interface, and the reagent spreading patterns after modification. The results indicate that for coal surfaces modified by non-polar n-octane, both the maximum adhesion force and the normalized triple-phase contact line (TPCL) at the coal-bubble interface increase with the enhancement of surface hydrophobicity. The maximum adhesion forces for strongly, moderately, and weakly hydrophobic surfaces were (79.01±2.80) , (66.07±5.52) , (58.15±3.30) μN, respectively, with normalized TPCL values of 1.05±0.01, 0.86±0.03, 0.79±0.04. For surfaces modified by polar n-octanol, the maximum adhesion force was positively correlated with hydrophobicity, reaching (112.97±5.25) , (92.21±4.63) , (75.98±4.29) μN, respectively; however, the normalized TPCL showed a non-linear relationship with hydrophobicity, with values of 1.13±0.02, 1.05±0.02, 1.06±0.01. AFM oil droplet probe tests revealed that n-octanol can adhere to both strongly and weakly hydrophobic coal surfaces at different driving velocities, though increased hydrodynamic forces lead to adhesion hysteresis. No direct adhesion was observed on moderately hydrophobic surfaces, but hydrodynamic forces could enhance the particle-droplet adhesion probability. The spreading degree of n-octanol was positively correlated with surface hydrophobicity. The modification efficiency of polar collectors is jointly governed by the particle-reagent adhesion probability and the degree of oil droplet spreading. Multi-scale force measurements can quantitatively reveal the microscopic mechanism of polar collectors in intensifying coal slime flotation, providing a scientific basis for the design and precise application of high-efficiency collectors for difficult-to-float coal slimes, such as low-rank and oxidized coals.