Details

Autor(en) / Beteiligte

• Fernández-Toledano, J-C.
• Blake, T.D.
• De Coninck, J.

Titel

Taking a closer look: A molecular-dynamics investigation of microscopic and apparent dynamic contact angles

Ist Teil von

• Journal of colloid and interface science, 2021-04, Vol.587, p.311-323

Ort / Verlag

United States: Elsevier Inc

Erscheinungsjahr

2021

Quelle

Access via ScienceDirect (Elsevier)

Beschreibungen/Notizen

• [Display omitted] Molecular dynamics (MD) may be used to investigate the velocity dependence of both the microscopic and apparent dynamic contact angles (θm and θapp). We use large-scale MD to explore the steady displacement of a water-like liquid bridge between two molecularly-smooth solid plates under the influence of an external force F0. A coarse-grained model of water reduces the computational demand and the solid-liquid affinity is varied to adjust the equilibrium contact angle θ0. Protocols are devised to measure θm and θapp as a function of contact-line velocity Ucl. For all θ0, θm is velocity-dependent and consistent with the molecular-kinetic theory of dynamic wetting (MKT). However, θapp diverges from θm as F0 is increased, especially at the receding meniscus. The behavior of θapp follows that predicted by Voinov: (θapp)3 = (θm)3 + 9Ca·ln(L/Lm), where Ca is the capillary number and L and Lm are suitably-chosen macroscopic and microscopic length scales. For each θ0, there is a critical velocity Ucrit and contact angle θcrit at which θapp→0 and the receding meniscus deposits a liquid film. Setting θapp=0, θm=θcrit and Ucl=Ucrit in the Voinov equation yields the value of L/Lm. The predicted values of θapp then agree well with those measured from the simulations. Since θm obeys the MKT, we have, therefore, demonstrated the utility of the combined model of dynamic wetting proposed by Petrov and Petrov.