Water–substrate physico-chemistry in wetting dynamics

2015 ◽  
Vol 781 ◽  
pp. 695-711 ◽  
Author(s):  
Petter Johansson ◽  
Andreas Carlson ◽  
Berk Hess
Keyword(s):  
Friction Factor ◽  
Contact Line ◽  
Continuum Model ◽  
Large Scale ◽  
Phase Field Model ◽  
Equilibrium Contact Angle ◽  
Wetting Front ◽  
Droplet Dynamics ◽  
Dynamics Simulations ◽  
Contact Line Friction

We consider the wetting of water droplets on substrates with different chemical composition and molecular spacing, but with an identical equilibrium contact angle. A combined approach of large-scale molecular dynamics simulations and a continuum phase field model allows us to identify and quantify the influence of the microscopic physics at the contact line on the macroscopic droplet dynamics. We show that the substrate physico-chemistry, in particular hydrogen bonding, can significantly alter the flow. Since the material parameters are systematically derived from the atomistic simulations, our continuum model has only one adjustable parameter, which appears as a friction factor at the contact line. The continuum model approaches the atomistic wetting rate only when we adjust this contact line friction factor. However, the flow appears to be qualitatively different when comparing the atomistic and continuum models, highlighting that non-trivial continuum effects can come into play near the interface of the wetting front.

scholarly journals Statics and dynamics of liquid barrels in wedge geometries

2018 ◽  
Vol 842 ◽  
pp. 26-57 ◽  
Author(s):  
Élfego Ruiz-Gutiérrez ◽  
Ciro Semprebon ◽  
Glen McHale ◽  
Rodrigo Ledesma-Aguilar
Keyword(s):  
Surface Energy ◽  
Liquid Droplet ◽  
Symmetry Plane ◽  
Equilibrium Contact Angle ◽  
Opening Angle ◽  
Lagrangian Description ◽  
Quasi Equilibrium ◽  
Droplet Dynamics ◽  
Statics And Dynamics ◽  
Contact Line Friction

We present a theoretical study of the statics and dynamics of a partially wetting liquid droplet, of equilibrium contact angle $\unicode[STIX]{x1D703}_{e}$, confined in a solid wedge geometry of opening angle $\unicode[STIX]{x1D6FD}$. We focus on a mostly non-wetting regime, given by the condition $\unicode[STIX]{x1D703}_{e}-\unicode[STIX]{x1D6FD}>90^{\circ }$, where the droplet forms a liquid barrel – a closed shape of positive mean curvature. Using a quasi-equilibrium assumption for the shape of the liquid–gas interface, we compute the changes to the surface energy and pressure distribution of the liquid upon a translation along the symmetry plane of the wedge. Our model is in good agreement with numerical calculations of the surface energy minimisation of static droplets deformed by gravity. Beyond the statics, we put forward a Lagrangian description of the droplet dynamics. We focus on the overdamped limit, where the driving capillary force is balanced by the frictional forces arising from the bulk hydrodynamics, the corner flow near the contact lines and the contact-line friction. Our results provide a theoretical framework to describe the motion of partially wetting liquids in confinement, and can be used to gain further understanding on the relative importance of dissipative processes that span from microscopic to macroscopic length scales.

Droplet Shapes on Superhydrophobic Surfaces Under Electrowetting Actuation

2011 ◽  
Author(s):  
S. Ravi Annapragada ◽  
Jayathi Y. Murthy ◽  
Suresh V. Garimella
Keyword(s):  
Contact Line ◽  
Intermediate Energy ◽  
Contact Angles ◽  
Superhydrophobic Surfaces ◽  
Droplet Dynamics ◽  
Droplet Shape ◽  
Structured Surfaces ◽  
Droplet Behavior ◽  
Wetting Process ◽  
Contact Line Friction

Droplet behavior on structured surfaces has recently generated a lot of interest due to its application to self-cleaning surfaces and in microfluidic devices. In this paper, the droplet shape and the droplet state on superhydrophobic surfaces are predicted using the Volume of Fluid (VOF) approach. Various structured surfaces are considered and the apparent contact angles are extracted from the predicted droplet shapes. Droplet dynamics under electrowetting are also modeled, including contact line friction. The model is validated against in-house experiments and experiments from the literature. The droplet state, droplet shape and apparent contact angles match well with the experimental measurements. The Cassie and Wenzel states on structured surfaces are also accurately predicted. Further, the electrowetting-induced transition from the Cassie to the Wenzel state and the reversal to the Cassie state is predicted for two different superhydrophobic surfaces. The transient wetting process, intermediate energy states and droplet shapes during electrowetting are simulated. The effective contact line friction coefficient on pillared surfaces is predicted to be 0.14 Ns/m2, consistent with published values.

scholarly journals Elucidating the Onset of Plasticity in Sliding Contacts Using Differential Computational Orientation Tomography

2021 ◽  
Vol 69 (3) ◽  
Author(s):  
S. J. Eder ◽  
P. G. Grützmacher ◽  
M. Rodríguez Ripoll ◽  
J. F. Belak
Keyword(s):  
Grain Boundary ◽  
Large Scale ◽  
Surface Deformation ◽  
Boundary Migration ◽  
Material Design ◽  
Lattice Rotation ◽  
Time Resolved ◽  
Near Surface ◽  
Color Saturation ◽  
Dynamics Simulations

Abstract Depending on the mechanical and thermal energy introduced to a dry sliding interface, the near-surface regions of the mated bodies may undergo plastic deformation. In this work, we use large-scale molecular dynamics simulations to generate “differential computational orientation tomographs” (dCOT) and thus highlight changes to the microstructure near tribological FCC alloy surfaces, allowing us to detect subtle differences in lattice orientation and small distances in grain boundary migration. The analysis approach compares computationally generated orientation tomographs with their undeformed counterparts via a simple image analysis filter. We use our visualization method to discuss the acting microstructural mechanisms in a load- and time-resolved fashion, focusing on sliding conditions that lead to twinning, partial lattice rotation, and grain boundary-dominated processes. Extracting and laterally averaging the color saturation value of the generated tomographs allows us to produce quantitative time- and depth-resolved maps that give a good overview of the progress and severity of near-surface deformation. Corresponding maps of the lateral standard deviation in the color saturation show evidence of homogenization processes occurring in the tribologically loaded microstructure, frequently leading to the formation of a well-defined separation between deformed and undeformed regions. When integrated into a computational materials engineering framework, our approach could help optimize material design for tribological and other deformation problems. Graphic Abstract .

scholarly journals Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth

2016 ◽  
Vol 34 (4) ◽  
pp. 041509 ◽  
Author(s):  
Daniel Edström ◽  
Davide G. Sangiovanni ◽  
Lars Hultman ◽  
Ivan Petrov ◽  
J. E. Greene ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Large Scale ◽  
Epitaxial Film ◽  
Film Growth ◽  
Dynamics Simulations ◽  
Epitaxial Film Growth

scholarly journals Experimental study of the contact line friction coefficient

2020 ◽  
Vol 1677 ◽  
pp. 012156
Author(s):  
N Sibiryakov ◽  
W Zheng ◽  
O Kabov ◽  
B Bai
Keyword(s):  
Experimental Study ◽  
Friction Coefficient ◽  
Contact Line ◽  
Contact Line Friction

scholarly journals Bimodal Grain-Size Scaling of Thermal Transport in Polycrystalline Graphene from Large-Scale Molecular Dynamics Simulations

Nano Letters ◽  
2017 ◽  
Vol 17 (10) ◽  
pp. 5919-5924 ◽  
Author(s):  
Zheyong Fan ◽  
Petri Hirvonen ◽  
Luiz Felipe C. Pereira ◽  
Mikko M. Ervasti ◽  
Ken R. Elder ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Grain Size ◽  
Molecular Dynamics Simulations ◽  
Thermal Transport ◽  
Large Scale ◽  
Size Scaling ◽  
Dynamics Simulations ◽  
Bimodal Grain Size
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