Pulsating flow driven alteration in moving contact-line dynamics on surfaces with patterned wettability gradients

2014 ◽  
Vol 116 (8) ◽  
pp. 084302 ◽  
Author(s):  
Pranab Kumar Mondal ◽  
Debabrata DasGupta ◽  
Aditya Bandopadhyay ◽  
Suman Chakraborty
Keyword(s):  
Contact Line ◽  
Pulsating Flow ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Contact Line Dynamics

Numerical investigations of electrothermally actuated moving contact line dynamics: Effect of property contrasts

2017 ◽  
Vol 29 (8) ◽  
pp. 082009 ◽  
Author(s):  
Golak Kunti ◽  
Anandaroop Bhattacharya ◽  
Suman Chakraborty
Keyword(s):  
Contact Line ◽  
Numerical Investigations ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Contact Line Dynamics

Contact Line Dynamics in Liquid-Vapor Flows Using Lattice Boltzmann Method

2006 ◽  
Author(s):  
Shi-Ming Li ◽  
Danesh K. Tafti
Keyword(s):  
Boundary Condition ◽  
Lattice Boltzmann Method ◽  
Contact Line ◽  
Lattice Boltzmann ◽  
Solid Wall ◽  
Hydrodynamic Theory ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Boltzmann Method ◽  
Contact Line Dynamics

A mean-field free-energy lattice Boltzmann method (LBM) is applied to simulate moving contact line dynamics. It is found that the common bounceback boundary condition leads to an unphysical velocity at the solid wall in the presence of surface forces. The magnitude of the unphysical velocity is shown proportional to the local force term. The velocity-pressure boundary condition is generalized to solve the problem of the unphysical velocity. The simulation results are compared with three different theories for moving contact lines, including a hydrodynamic theory, a molecular kinetic theory, and a linear cosine law of moving contact angle versus capillary number. It is shown that the current LBM can be used to replace the three theories in handling moving contact line problems.

Electrothermally actuated moving contact line dynamics over chemically patterned surfaces with resistive heaters

2018 ◽  
Vol 30 (6) ◽  
pp. 062004 ◽  
Author(s):  
Golak Kunti ◽  
Anandaroop Bhattacharya ◽  
Suman Chakraborty
Keyword(s):  
Contact Line ◽  
Patterned Surfaces ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Chemically Patterned Surfaces ◽  
Contact Line Dynamics

scholarly journals Thermodynamically consistent modelling of two-phase flows with moving contact line and soluble surfactants

2019 ◽  
Vol 879 ◽  
pp. 327-359 ◽  
Author(s):  
Guangpu Zhu ◽  
Jisheng Kou ◽  
Bowen Yao ◽  
Yu-shu Wu ◽  
Jun Yao ◽  
...  
Keyword(s):  
Contact Line ◽  
Phase Field ◽  
Surfactant Adsorption ◽  
Line Model ◽  
Droplet Dynamics ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Soluble Surfactants ◽  
Flow States ◽  
Contact Line Dynamics

Droplet dynamics on a solid substrate is significantly influenced by surfactants. It remains a challenging task to model and simulate the moving contact line dynamics with soluble surfactants. In this work, we present a derivation of the phase-field moving contact line model with soluble surfactants through the first law of thermodynamics, associated thermodynamic relations and the Onsager variational principle. The derived thermodynamically consistent model consists of two Cahn–Hilliard type of equations governing the evolution of interface and surfactant concentration, the incompressible Navier–Stokes equations and the generalized Navier boundary condition for the moving contact line. With chemical potentials derived from the free energy functional, we analytically obtain certain equilibrium properties of surfactant adsorption, including equilibrium profiles for phase-field variables, the Langmuir isotherm and the equilibrium equation of state. A classical droplet spread case is used to numerically validate the moving contact line model and equilibrium properties of surfactant adsorption. The influence of surfactants on the contact line dynamics observed in our simulations is consistent with the results obtained using sharp interface models. Using the proposed model, we investigate the droplet dynamics with soluble surfactants on a chemically patterned surface. It is observed that droplets will form three typical flow states as a result of different surfactant bulk concentrations and defect strengths, specifically the coalescence mode, the non-coalescence mode and the detachment mode. In addition, a phase diagram for the three flow states is presented. Finally, we study the unbalanced Young stress acting on triple-phase contact points. The unbalanced Young stress could be a driving or resistance force, which is determined by the critical defect strength.

Contact-line dynamics of a diffuse fluid interface

2000 ◽  
Vol 402 ◽  
pp. 57-88 ◽  
Author(s):  
DAVID JACQMIN
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Chemical Potential ◽  
Equilibrium Contact Angle ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Potential Gradients ◽  
Inner Region ◽  
Chemical Potential Gradients ◽  
Contact Line Dynamics

An investigation is made into the moving contact line dynamics of a Cahn–Hilliard–van der Waals (CHW) diffuse mean-field interface. The interface separates two incompressible viscous fluids and can evolve either through convection or through diffusion driven by chemical potential gradients. The purpose of this paper is to show how the CHW moving contact line compares to the classical sharp interface contact line. It therefore discusses the asymptotics of the CHW contact line velocity and chemical potential fields as the interface thickness ε and the mobility κ both go to zero. The CHW and classical velocity fields have the same outer behaviour but can have very different inner behaviours and physics. In the CHW model, wall–liquid bonds are broken by chemical potential gradients instead of by shear and change of material at the wall is accomplished by diffusion rather than convection. The result is, mathematically at least, that the CHW moving contact line can exist even with no-slip conditions for the velocity. The relevance and realism or lack thereof of this is considered through the course of the paper.The two contacting fluids are assumed to be Newtonian and, to a first approximation, to obey the no-slip condition. The analysis is linear. For simplicity most of the analysis and results are for a 90° contact angle and for the fluids having equal dynamic viscosity μ and mobility κ. There are two regions of flow. To leading order the outer-region velocity field is the same as for sharp interfaces (flow field independent of r) while the chemical potential behaves like r−ξ, ξ = π/2/max{θeq, π − θeq}, θeq being the equilibrium contact angle. An exception to this occurs for θeq = 90°, when the chemical potential behaves like ln r/r. The diffusive and viscous contact line singularities implied by these outer solutions are resolved in the inner region through chemical diffusion. The length scale of the inner region is about 10√μκ – typically about 0.5–5 nm. Diffusive fluxes in this region are O(1). These counterbalance the effects of the velocity, which, because of the assumed no-slip boundary condition, fluxes material through the interface in a narrow boundary layer next to the wall.The asymptotic analysis is supplemented by both linearized and nonlinear finite difference calculations. These are made at two scales, experimental and nanoscale. The first set is done to show CHW interface behaviour and to test the qualitative applicability of the CHW model and its asymptotic theory to practical computations of experimental scale, nonlinear, low capillary number flows. The nanoscale calculations are carried out with realistic interface thicknesses and diffusivities and with various assumed levels of shear-induced slip. These are discussed in an attempt to evaluate the physical relevance of the CHW diffusive model. The various asymptotic and numerical results together indicate a potential usefullness for the CHW model for calculating and modelling wetting and dewetting flows.

Moving contact line

2001 ◽  
Vol 11 (PR6) ◽  
pp. Pr6-199-Pr6-212 ◽  
Author(s):  
Y. Pomeau
Keyword(s):  
Contact Line ◽  
Moving Contact Line ◽  
Moving Contact

scholarly journals Existence of Moffatt vortices at a moving contact line between two fluids

2017 ◽  
Vol 2 (11) ◽  
Author(s):  
Mijail Febres ◽  
Dominique Legendre
Keyword(s):  
Contact Line ◽  
Two Fluids ◽  
Moving Contact Line ◽  
Moving Contact

scholarly journals Validation and modification of asymptotic analysis of slow and rapid droplet spreading by numerical simulation

2013 ◽  
Vol 715 ◽  
pp. 283-313 ◽  
Author(s):  
Yi Sui ◽  
Peter D. M. Spelt
Keyword(s):  
Numerical Simulation ◽  
Asymptotic Analysis ◽  
Contact Line ◽  
Slip Length ◽  
Interface Shape ◽  
Droplet Spreading ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Line Region ◽  
Modified Theory

AbstractUsing a slip-length-based level-set approach with adaptive mesh refinement, we have simulated axisymmetric droplet spreading for a dimensionless slip length down to $O(1{0}^{\ensuremath{-} 4} )$. The main purpose is to validate, and where necessary improve, the asymptotic analysis of Cox (J. Fluid Mech., vol. 357, 1998, pp. 249–278) for rapid droplet spreading/dewetting, in terms of the detailed interface shape in various regions close to the moving contact line and the relation between the apparent angle and the capillary number based on the instantaneous contact-line speed, $\mathit{Ca}$. Before presenting results for inertial spreading, simulation results are compared in detail with the theory of Hocking & Rivers (J. Fluid Mech., vol. 121, 1982, pp. 425–442) for slow spreading, showing that these agree very well (and in detail) for such small slip-length values, although limitations in the theoretically predicted interface shape are identified; a simple extension of the theory to viscous exterior fluids is also proposed and shown to yield similar excellent agreement. For rapid droplet spreading, it is found that, in principle, the theory of Cox can predict accurately the interface shapes in the intermediate viscous sublayer, although the inviscid sublayer can only be well presented when capillary-type waves are outside the contact-line region. However, $O(1)$ parameters taken to be unity by Cox must be specified and terms be corrected to ${\mathit{Ca}}^{+ 1} $ in order to achieve good agreement between the theory and the simulation, both of which are undertaken here. We also find that the apparent angle from numerical simulation, obtained by extrapolating the interface shape from the macro region to the contact line, agrees reasonably well with the modified theory of Cox. A simplified version of the inertial theory is proposed in the limit of negligible viscosity of the external fluid. Building on these results, weinvestigate the flow structure near the contact line, the shear stress and pressure along the wall, and the use of the analysis for droplet impact and rapid dewetting. Finally, we compare the modified theory of Cox with a recent experiment for rapid droplet spreading, the results of which suggest a spreading-velocity-dependent dynamic contact angle in the experiments. The paper is closed with a discussion of the outlook regarding the potential of using the present results in large-scale simulations wherein the contact-line region is not resolved down to the slip length, especially for inertial spreading.

Depletion of λ-DNA near moving contact line

2016 ◽  
Vol 236 ◽  
pp. 50-62
Author(s):  
Hongrok Shin ◽  
Ki Wan Bong ◽  
Chongyoup Kim
Keyword(s):  
Contact Line ◽  
Moving Contact Line ◽  
Moving Contact

A gradient stable scheme for a phase field model for the moving contact line problem

2012 ◽  
Vol 231 (4) ◽  
pp. 1372-1386 ◽  
Author(s):  
Min Gao ◽  
Xiao-Ping Wang
Keyword(s):  
Contact Line ◽  
Phase Field ◽  
Field Model ◽  
Phase Field Model ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Stable Scheme
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