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

Abstract

Superspreading is the rapid and complete spreading of surfactant-laden droplets on hydrophobic substrates. This phenomenon has been studied for many decades by experiment, theory, and simulation, but it has been only recently that molecular-level simulation has provided significant insights into the underlying mechanisms of superspreading thanks to the development of accurate force-fields and the increase of computational capabilities. Here, we review the main advances in this area that have surfaced from Molecular Dynamics simulation of all-atom and coarse-grained models highlighting and contrasting the main results and discussing various elements of the proposed mechanisms for superspreading. We anticipate that this review will stimulate further research on the interpretation of experimental results and the design of surfactants for applications requiring efficient spreading, such as coating technology.

Molecular dynamics simulation of the coalescence of surfactant-laden droplets

“…70–75 More specifically, a force-field based on the SAFT-γ Mie theory 76 is used, which can accurately reproduce relevant key properties of water–surfactant systems, such as their phase behaviour and surface tension. 5,67,77–79…”

“…1,2 In contrast, speeding up the rate of coalescence by adding surfactant could be advantageous in applications, such as coatings 3 and superspreading. 4,5…”

“…1,2 In contrast, speeding up the rate of coalescence by adding surfactant could be advantageous in applications, such as coatings 3 and superspreading. 4,5 Experimental, theoretical, and numerical studies of coalescing droplets have thus far mainly focused on cases without additives, e.g. water or polymer droplets.…”

Coupled Flow and Heat or Mass Transfer

“…In microfluidics, Theodorakis et al [2] reviewed recent molecular-level simulation techniques for the probing of the rapid and complete spreading of surfactant-laden droplets on hydrophobic surfaces-a phenomenon known for many years as superspreading, but only recently tackled with molecular simulations. The thorough character of this review makes it valuable for investigators in coating technologies, and also to investigators interested in advancing the field of fluid-substrate interactions with computations, since it identified the bottlenecks that require further research.…”

“…The behavior of oil, water, and surfactant molecules in tight pores that are common in shale rocks was probed to determine the effect of viscous forces on oil mobilization. While Theodorakis et al [2], Yamada et al [3], and Bui et al [4] utilized molecular level numerical techniques, such as MD and DPD, Vlachomitrou & Pelekasis [5] and Dobri & Papathanasiou [6] employed numerical techniques that are appropriate for larger scales. Vlachomitrou & Pelekasis [5] investigated the unsteady flow of a liquid metal inside a single pore in the presence of magnetic forces with a numerical approach.…”