Line tension at wetting: interface displacement model beyond the gradient-squared approximation

• Published in: Physica A 1993-12, Vol.201 (4), p.457-481
• Main Authors: Dobbs, H.T., Indekeu, J.O.
• Format: Article
• Language: English
• Subjects: Critical point phenomena; Exact sciences and technology; Phase transitions: general studies; Physics; Statistical physics, thermodynamics, and nonlinear dynamical systems; Thermodynamics
• ISSN: 0378-4371; 1873-2119
• DOI: 10.1016/0378-4371(93)90120-S

We study the transition zone or contact line between a thin film and bulk liquid, and calculate the line tension τ, employing an interface displacement model equivalent to Derjaguin's and de Gennes' approach. We investigate the behaviour of τ in the limit that the contact angle ϑ tends to zero, approaching a wetting phase transition. Previous results for wetting and prewetting, derived in the gradient-squared approximation of the model, remain valid when the gradient is included to all orders. The interesting singular behaviour of τ at wetting is universal, due to the critical phenomena that have recently been found to underly first-order as well as continuous wetting transitions. Finally we critically review two contact-line instabilities that have been associated with contact-angle hysteresis, and propose an alternative physical interpretation.