Molecular dynamics simulations of the contact angle between water droplets and graphite surfaces

Sergi, Danilo; Scocchi, Giulio; Ortona, Alberto

doi:10.1016/j.fluid.2012.07.010

Cited by 69 publications

(53 citation statements)

References 24 publications

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“…We also estimate k I for these systems, and find any differences across different inter-surface separation are within the statistical uncertainty. Although estimates of k I and k D agree reasonably well with k F , the necessity of having to choose a contact plane introduces an inherent ambiguity in the determination of contact angles from geometric approaches [59][60][61] . Such ambiguity is expected to introduce systematic errors in contact angle estimates obtained from geometry-based methods.…”

Section: Lj Surfaces With a Wide Range Of Surface-water Attractionsmentioning

confidence: 85%

Characterizing surface wetting and interfacial properties using enhanced sampling (SWIPES)

et al. 2019

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We introduce an accurate and efficient method for characterizing surface wetting and interfacial properties, such as the contact angle made by a liquid droplet on a solid surface, and the vapor-liquid surface tension of a fluid. The method makes use of molecular simulations in conjunction with the indirect umbrella sampling technique to systematically wet the surface and estimate the corresponding free energy. To illustrate the method, we study the wetting of a family of Lennard-Jones surfaces by water. We estimate contact angles for surfaces with a wide range of attractions for water by using our method and also by using droplet shapes. Notably, as surface -water attractions are increased, our method is able to capture the transition from partial to complete wetting. Finally, the method is straightforward to implement and computationally efficient, providing accurate contact angle estimates in roughly 5 nanoseconds of simulation time. A. IntroductionWetting of solid surfaces by fluids is important in diverse disciplines, including but not limited to surface chemistry, materials characterization, oil and gas recovery 1-5 . In general, the wettability of a solid by a fluid is characterized by a wetting coefficient, k ≡ (γ SV − γ SL )/γ VL , where γ represents surface tension, and the subscripts correspond to the coexisting vapor (V), liquid (L) and solid (S) phases. The wetting coefficient is also related to the contact angle (θ ) that a liquid droplet (surrounded by its vapor) makes with a solid surface; according to Young's equation, cos θ = (γ SV − γ SL )/γ VL = k. Thus, the extent to which a fluid prefers to wet a solid, or the preference of the solid for the

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Section: Lj Surfaces With a Wide Range Of Surface-water Attractionsmentioning

confidence: 85%

Characterizing surface wetting and interfacial properties using enhanced sampling (SWIPES)

et al. 2019

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“…Such an approach, although appealing from the simplicity of the method, provides inconsistent results, particularly for small droplets [11]. Understandingly, different methods of increasing complexity have been devised for this purpose [15][16][17]. Figure 3 illustrates the difficulties associated with defining the contact angle using two-dimensional slices of molecular snapshots, especially for small droplets.…”

Section: Introductionmentioning

confidence: 99%

On the Calculation of Solid-Fluid Contact Angles from Molecular Dynamics

Santiso

Herdes

Müller

2013

Entropy

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Abstract:A methodology for the determination of the solid-fluid contact angle, to be employed within molecular dynamics (MD) simulations, is developed and systematically applied. The calculation of the contact angle of a fluid drop on a given surface, averaged over an equilibrated MD trajectory, is divided in three main steps: (i) the determination of the fluid molecules that constitute the interface, (ii) the treatment of the interfacial molecules as a point cloud data set to define a geometric surface, using surface meshing techniques to compute the surface normals from the mesh, (iii) the collection and averaging of the interface normals collected from the post-processing of the MD trajectory. The average vector thus found is used to calculate the Cassie contact angle (i.e., the arccosine of the averaged normal z-component). As an example we explore the effect of the size of a drop of water on the observed solid-fluid contact angle. A single coarsegrained bead representing two water molecules and parameterized using the SAFT-γ Mie equation of state (EoS) is employed, meanwhile the solid surfaces are mimicked using integrated potentials. The contact angle is seen to be a strong function of the system size for small nano-droplets. The thermodynamic limit, corresponding to the infinite size (macroscopic) drop is only truly recovered when using an excess of half a million water coarse-grained beads and/or a drop radius of over 26 nm.

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“…By using the algorithm rRESPA reference system propagator algorithm, the spread of pure water droplets on graphitic surfaces can be studied. Using numerical integration with multiple time step sizes, the initial transition radius of the droplet ranging from 20 to 80 nm could be revealed 26 . Based on the multicomponent and multiphase Lattice Boltzmann schemes, the accuracy of the numerical simulation could be enhanced to only 10-20% error for contact angle prediction 27 .…”

Section: Materials and Methods Surface Contact Angle Theorymentioning

confidence: 99%

A designable surface via the micro-molding process

Wang

et al. 2018

Microsyst Nanoeng

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A rapid prototyping process was presented to fabricate a nylon honeycomb microstructure coated with parylene C. The surface structure was designed to obtain a hydrophobic surface using the volume of fluid (VOF) model. With the micro-molding technique, the contact angle of the polymer surface could be designed and fabricated by changing the different microstructure surface diesteel mold inserts. For the honeycomb (20 μm width and 60 μm depth) microcavity side wall, an average micro-molding filling percentage of 95% could be achieved by using a three-section constant-pressure molding process. The solid surface wettability is governed by both the geometrical microstructures and the surface energy. A 2 μm parylene C layer was deposited on the nylon honeycomb microsurface to reduce the surface energy. To design honeycomb structures with different microcavity densities, the contact angle of these artificial surfaces could change from 91°to 130°. From a comparison of the contact angle measurements with the different models, the honeycomb-structured microsurface could be described by the Cassie-Baxter model. The errors between the VOF simulation and the measured data were o 10%. The drag reduction performance of the honeycomb microplates was investigated in a water tunnel with a high Reynolds number (from 0.5 × 10 6 to 4.6 × 10 6 ). As a result, the honeycomb microplates showed a maximum drag reduction rate of 36 ± 0.6% in comparison with the bare plates in such turbulent flow. Benefiting from the replaceable mold insert, more designable microstructure polymer surfaces can be manufactured by this rapid prototyping technique.

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Molecular dynamics simulations of the contact angle between water droplets and graphite surfaces

Cited by 69 publications

References 24 publications

Characterizing surface wetting and interfacial properties using enhanced sampling (SWIPES)

Characterizing surface wetting and interfacial properties using enhanced sampling (SWIPES)

On the Calculation of Solid-Fluid Contact Angles from Molecular Dynamics

A designable surface via the micro-molding process

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