Moving Contact Lines: Linking Molecular Dynamics and Continuum-Scale Modeling

Abstract

Despite decades of research, the modeling of moving contact lines has remained a formidable challenge in fluid dynamics whose resolution will impact numerous industrial, biological, and daily life applications. On the one hand, molecular dynamics (MD) simulation has the ability to provide unique insight into the microscopic details that determine the dynamic behavior of the contact line, which is not possible with either continuum-scale simulations or experiments. On the other hand, continuum-based models provide a link to the macroscopic description of the system. In this Feature Article, we explore the complex range of physical factors, including the presence of surfactants, which governs the contact line motion through MD simulations. We also discuss links between continuum- and molecular-scale modeling and highlight the opportunities for future developments in this area.

Molecular Dynamics Simulation of the Superspreading of Surfactant-Laden Droplets. A Review

“…Nowadays, the existence of reliable force-fields for water-surfactant systems based on all-atom [39][40][41][42] and coarse-grained (CG) models [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] enable the genuine simulation of such systems. For example, recent simulations of aqueous solutions with surfactants [21,22,[61][62][63][64][65][66][67] have established the connection between the behaviour of surfactants in the bulk and spreading [68][69][70][71], while the superspreading mechanism and the main characteristics of superspreading surfactants have been the focus of recent studies [5,[19][20][21][22][23][24]68,[70][71][72]. In view of these important advances in the superspreading arena, this review will highlight what we believe a...…”

“…The SAFT CG force-field has been used for the study of water-surfactant systems [19,66,67,[101][102][103] and particularly in the context of superspreading (Figure 4) [5,19,20,26,72]. This CG model is derived from the SAFT-γ molecular-based equation of state (EoS), which can describe analytically experimental data [104,105].…”

“…Recent studies by Theodorakis et al [5,19,20,26,72] that are based on MD simulation of the SAFT CG force-field have provided useful insights into the underlying microscopic mechanisms of superspreading [5]. The suitability of the SAFT force-field and the large size of the droplets allowed by the CG model offered opportunities to monitor various adsorption processes within the droplet, which are relevant for superspreading.…”

“…However, the amount of available computational resources pose severe limitations on the choice of the droplet size, given a number of parameters which could be explored, such as surfactant concentrations as well as different surfactants with different lengths and chemical groups. To this end, methods that couple MD and continuum simulation for systems of water-surfactant droplets may become routine in the years to come [72]. However, such multiscale algorithms are still challenging for systems with surfactant.…”

An energy stable C0 finite element scheme for a quasi-incompressible phase-field model of moving contact line with variable density

“…Applications of MCLs in industries and medical fields (for example, printing [3], spray cooling of surfaces [4], blood clot [5], microfluidics [6], surfactant [7,8]) have motivated scientific interests and mathematical challenges on associated issues such as the stress singularity and contact angle hysteresis. In order to model the dynamics around the contact lines, various types of models and approximations have been developed, such as direct molecular dynamics simulations [9,10,11], phase-filed models [12,13,14,15,16,17], microscopic-macroscopic hybrid model [18,19], front tracking model [20,21,22,8] and Lattice Boltzmann model [23]. For reviews of the current status of the MCLs problem, we refer to the articles [24] and [25].…”