Line tension near the wetting transition: results from an interface displacement model

An interface displacement model is employed for calculating the line tension of a contact line where three phases meet. At a first-order wetting transition the line tension reaches a positive and finite limit if the intermolecular potentials decay faster than r−6. In contrast, for non-retarder Van der Waals forces, and forces of still longer range, the line tension diverges at first-order wetting. The boundary tension along the prewetting line is positive and finite. Approaching wetting, it increases (with diverging slope) and converges to the value of the line tension at first-order wetting. Approaching first-order wetting at bulk phase coexistence, the line tension is finite provided the potentials decay faster than r−5, and increases (with diverging slope) towards its limit at wetting. In contrast, at a critical wetting transition the line tension vanishes. Comparison with recent results from alternative microscopic mean-field approximations is favourable.