Line tension at high contact angle wetting: Contribution to interfacial energy at long distances (≫100 Å) from the triple line contour

We measured water/air interfacial energy as functions of the finest texture radius of annealed PTFE substrates where air bubbles are anchored. The calculated line tension from measured force vs distance curves for a 7 nm PTFE substrate texture radius is (28 ± 8) × 10−9 N. However, the most surprising aspect is that this effect is not restricted to the triple line vicinity, previously estimated to be ∼100 Å but spreads all over the water/air bubble interface. The proposed method is an alternative to the controversial contact angle measurement for estimating the line tension contribution.