Stick-Slip Motion of Moving Contact Line on Chemically Patterned Surfaces

Abstract

Abstract. Based on our continuum hydrodynamic model for immiscible two-phase flows at solid surfaces, the stick-slip motion has been predicted for moving contact line at chemically patterned surfaces [Wang et al., J. Fluid Mech., 605 (2008), pp. 59-78]. In this paper we show that the continuum predictions can be quantitatively verified by molecular dynamics (MD) simulations. Our MD simulations are carried out for two immiscible Lennard-Jones fluids confined by two planar solid walls in Poiseuille flow geometry. In particular, one solid surface is chemically patterned with alternating stripes. For comparison, the continuum model is numerically solved using material parameters directly measured in MD simulations. From oscillatory fluid-fluid interface to intermittent stick-slip motion of moving contact line, we have quantitative agreement between the continuum and MD results. This agreement is attributed to the accurate description down to molecular scale by the generalized Navier boundary condition in our continuum model. Numerical results are also presented for the relaxational dynamics of fluid-fluid interface, in agreement with a theoretical analysis based on the Onsager principle of minimum energy dissipation.

An augmented method for free boundary problems with moving contact lines

“…In additional to imposing the Navier slip boundary condition on the solid wall to remove force singularity, the contact line dynamics must also be prescribed. In the presence of contact angle hysteresis, one can prescribe the contact angle depending on the sign of contact line speed [31,22,8,32]. In the above models, however, the advancing and receding contact angles must be given.…”

Effective boundary conditions for dynamic contact angle hysteresis on chemically inhomogeneous surfaces

“…Firstly, on the chemically patterned surfaces, the slip velocity is still bounded due to the friction of the contact line. Previous molecular dynamics simulations and those based on continuum models show that the maximal slip velocity is a few times larger than that in steady state (Wang et al 2008;Wu et al 2010;Ren & E 2011). In this case, the difference between the original Cox's formula (2.8) and the modified formula (4.6) with inertial effects may not be very large.…”

Dripping and Jetting in Coflowing Liquid Streams

“…In our calculations, the values of the first four parameters are taken from those determined through MD simulations of moving contact line problem [Qian et al (2003)] (used also in [Qian et al (2009);Wang et al (2008); Wu et al (2010)]). They are L d = 5, R = 0.03, B = 12, and V s = 5, with the length scale ξ = 1/3σ and the velocity scale V = 0.25 /m (in which and σ are energy and length scales, respectively in the Lennard-Jones potential for fluid molecules and m is the fluid molecular mass).…”