Molecular Dynamics Simulation of Ultra-Fast Phase Transition in Water Nanofilms

2020 ◽  
Author(s):  
Malcolm Porterfield ◽  
Diana Borca-Tasciuc
Keyword(s):  
Molecular Dynamics ◽  
Contact Angle ◽  
Morse Potential ◽  
Water Film ◽  
Contact Angles ◽  
Gold Substrate ◽  
Explosive Boiling ◽  
Interaction Sites ◽  
Lennard Jones ◽  
Water Films

Abstract Molecular dynamics simulations are used to explore explosive boiling of thin water films on a gold substrate. In particular, water films of 2.5, 1.6 and 0.7 nanometer thickness were examined. Three different surface wettabilities with contact angles of 11, 47 and 110 degrees were simulated along with substrate temperatures of 400K, 600K, 800K and 1000K. The 11 degree contact angle was obtained using a Morse interaction potential between the water film and the gold substrate while the 47 and 110 degree contact angles were obtained via a Lennard-Jones potential. Evaporation was the first mode of phase change observed in all cases and explosive boiling did not occur until the substrate reached a temperature of 800K. When explosive boiling was present for all three contact angles, it was consistently shown to occur first for the surface with a 47 degree contact angle, contrary to the expectation that it would occur first on the substrate with an 11 degree contact angle. These results suggest that explosive boiling onset is strongly dependent on the particularities of the interaction potential. For instance, the Morse potential used to model the surface described by an 11 degree contact angle, is a softer potential as compared with Lennard-Jones, but has more interaction sites per molecule — two hydrogen atoms and one oxygen atom vs one oxygen atom. Thus, although the water film reaches a higher temperature with the Morse potential, explosive boiling onset is delayed as more interaction sites have to be disrupted. These results suggest that both the interaction strength and the number of atoms interacting at the interface must be considered when investigating trends of explosive boiling with surface wettability.

Molecular Dynamics Simulation of Ultra-Fast Phase Transition in Water Nanofilms

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Malcolm Porterfield ◽  
Diana-Andra Borca-Tasciuc
Keyword(s):  
Morse Potential ◽  
Water Film ◽  
Contact Angles ◽  
Lennard Jones Potential ◽  
Gold Substrate ◽  
Jones Potential ◽  
Explosive Boiling ◽  
Interaction Sites ◽  
Lennard Jones ◽  
Water Films

Abstract Molecular dynamics simulations are used to explore explosive boiling of thin water films on a gold substrate. In particular, water films of 0.7, 1.6, and 2.5 nanometer thickness were examined. Three different surface wettabilities with contact angles of 11 deg, 47 deg, and 110 deg were simulated along with substrate temperatures of 400 K, 600 K, 800 K, and 1000 K. The 11 and 47 deg contact angles were obtained using a Morse interaction potential between the water film and gold substrate while the 47 and 110 deg contact angles were obtained via a Lennard-Jones potential. Evaporation was the first mode of phase change observed in all cases and explosive boiling did not occur until the substrate reached a temperature of 800 K. When explosive boiling was present for all three contact angles, it was consistently shown to occur first for the surface with a 47 deg contact angle and Lennard-Jones potential. These results suggest that explosive boiling onset is strongly dependent on the particularities of the interaction potential. For instance, the Morse potential is smoother when compared to the Lennard-Jones potential, but has more interaction sites per molecule—two hydrogen atoms and one oxygen atom versus one oxygen atom. Thus, even when the water film reaches a higher temperature with the Morse potential, explosive boiling onset is delayed as more interaction sites have to be disrupted. These results suggest that contact angle alone is insufficient and both the interaction strength and the number of atoms interacting at the interface must be considered when investigating trends of explosive boiling with surface wettability.

scholarly journals Molecular Dynamics Simulation of Wetting Behavior: Contact Angle Dependency on Water Potential Models

2021 ◽  
Vol 1 (1) ◽  
pp. 10
Author(s):  
Lukman Hakim ◽  
Irsandi Dwi Oka Kurniawan ◽  
Ellya Indahyanti ◽  
Irwansyah Putra Pradana
Keyword(s):  
Molecular Dynamics ◽  
Contact Angle ◽  
Liquid Droplet ◽  
Center Of Mass ◽  
Contact Angles ◽  
Surface Wettability ◽  
Dynamics Simulation ◽  
Potential Models ◽  
Surface Hydrophilicity ◽  
Dynamics Simulations

The underlying principle of surface wettability has obtained great attentions for the development of novel functional surfaces. Molecular dynamics simulations has been widely utilized to obtain molecular-level details of surface wettability that is commonly quantified in term of contact angle of a liquid droplet on the surface. In this work, the sensitivity of contact angle calculation at various degrees of surface hydrophilicity to the adopted potential models of water: SPC/E, TIP4P, and TIP5P, is investigated. The simulation cell consists of a water droplet on a structureless surface whose hydrophilicity is modified by introducing a scaling factor to the water-surface interaction parameter. The simulation shows that the differences in contact angle described by the potential models are systematic and become more visible with the increase of the surface hydrophilicity. An alternative method to compute a contact angle based on the height of center-of-mass of the droplet is also evaluated, and the resulting contact angles are generally larger than those determined from the liquid-gas interfacial line.

Rheological Properties of Water Films Nanoconfined in Parallel Au Plates by Molecular Dynamics Simulations

2007 ◽  
Vol 121-123 ◽  
pp. 1109-1114
Author(s):  
M.L. Liao ◽  
Shin Pon Ju ◽  
Jenn Sen Lin ◽  
Y.S. Lin
Keyword(s):  
Molecular Dynamics ◽  
Shear Rate ◽  
Molecular Dynamics Simulations ◽  
Rheological Properties ◽  
Shear Viscosity ◽  
Water Film ◽  
Water Molecules ◽  
Water Films ◽  
Dynamics Simulations ◽  
And Diffusion

Rheological properties of water films nanoconfined in two parallel Au plates are investigated with the aid of molecular dynamics simulations. The density distribution, velocity profile, and diffusion coefficients of the water film in a Couette flow are studied. Shear viscosity and its dependence on the shear rate of the water film are also examined in the present research. It is found that the density of the water molecules near the plates is much higher than that in the other regions. This indicates that many water molecules are adsorbed by the plates and adsorbed layers are formed in the vicinity of the plates. The diffusion of the whole film increases dramatically as the shear rate becomes greater than 1010 s-1. The shear viscosity decreases as the shear rate increases, especially for the water film with a small thickness, which indicates the shear-thinning behavior for viscosity of the nanoconfined film. Moreover, an increase in shear viscosity with a decrease in the film thickness can also be found in the present study.

scholarly journals Molecular Dynamics Study of Adsorption of the Lennard-Jones Truncated and Shifted Fluid on Planar Walls

2021 ◽  
Author(s):  
Michaela Heier ◽  
Felix Diewald ◽  
Martin Horsch ◽  
Kai Langenbach ◽  
Ralf Müller ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Gas Phase ◽  
Saturation Pressure ◽  
Contact Angles ◽  
Surface Excess ◽  
Lennard Jones ◽  
Partial Wetting ◽  
Adsorbed Layers ◽  
Cutoff Radius ◽  
Fluid Interaction

A comprehensive molecular dynamics study of gas phase and supercritical fluid adsorption on planar walls in dispersive systems is presented. All interactions in the system are described with the Lennard-Jones truncated and shifted (LJTS) potential with a cutoff radius of 2.5 fluid diameters. The adsorption strength is characterized by the solid-fluid interaction energy and the wall density. Both parameters are varied systematically. The present work extends a previous study in which wetting in the same systems was investigated. Therefore, the contact angles are known for all studied systems. They include cases with total wetting as well as cases with partial wetting. The temperature varies between the triple point and 3 times the critical temperature of the LJTS fluid. For the systems with partial wetting, the adsorption is studied not only up to the saturation pressure but also in the metastable region. For all systems, the surface excess is determined as a function of pressure and temperature. Furthermore, data on the thickness and structure of the adsorbed layers is reported. In some of the systems, prewetting is observed.

scholarly journals The Effect of Water Droplet Size, Temperature, and Impingement Velocity on Gold Wettability at the Nanoscale

2017 ◽  
Vol 5 (3) ◽  
Author(s):  
Jhonatam Cordeiro ◽  
Salil Desai
Keyword(s):  
Contact Angle ◽  
Droplet Size ◽  
Water Droplet ◽  
Molecular Diffusion ◽  
Dynamic Contact Angle ◽  
Contact Angles ◽  
Gold Substrate ◽  
Stabilization Time ◽  
Lower Contact ◽  
Impingement Velocity

Molecular dynamics (MD) simulations are performed to investigate the wettability of gold substrate interacting with nanosized droplets of water. The effects of droplet size, temperature variation, and impingement velocity are evaluated using molecular trajectories, dynamic contact angle, spread ratios, radial distribution function (RDF), and molecular diffusion graphs. Droplets of 4 nm and 10 nm were simulated at 293 K and 373 K, respectively. Stationary droplets were compared to droplets impinging the substrate at 100 m/s. The simulations were executed on high-end workstations equipped with NVIDIA® Tesla graphical processing units (GPUs). Results show that smaller droplets have a faster stabilization time and lower contact angles than larger droplets. With an increase in temperature, stabilization time gets faster, and the molecular diffusion from the water droplet increases. Higher temperatures also increase the wettability of the gold substrate, wherein droplets present a lower contact angle and a higher spread ratio. Droplets that impact the substrate at a higher impingement velocity converge to the same contact angle as stationary droplets. At higher temperatures, the impingement velocities accelerate the diffusion of water molecules into vapor. It was revealed that impingement velocities do not influence stabilization times. This research establishes relationships among different process parameters to control the wettability of water on gold substrates which can be explored to study several nanomanufacturing processes.

scholarly journals Contact angle and adsorption energies of nanoparticles at the air–liquid interface determined by neutron reflectivity and molecular dynamics

Nanoscale ◽  
2015 ◽  
Vol 7 (13) ◽  
pp. 5665-5673 ◽  
Author(s):  
Javier Reguera ◽  
Evgeniy Ponomarev ◽  
Thomas Geue ◽  
Francesco Stellacci ◽  
Fernando Bresme ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Contact Angle ◽  
Contact Angles ◽  
Liquid Interface ◽  
Neutron Reflectivity ◽  
New Approach ◽  
Adsorption Energies ◽  
Air Liquid Interface

A new approach, based on in situ neutron reflectivity and molecular dynamics has been developed for calculating contact angles of nanoparticles at interfaces.

Simulation of Water Flow in a Coated Nano Pore by a Molecular Dynamics

2008 ◽  
Vol 57 ◽  
pp. 73-79
Author(s):  
K. Yamamoto ◽  
T. Iwatsubo ◽  
Ken-ichi Saitoh ◽  
T. Moriuchi
Keyword(s):  
Molecular Dynamics ◽  
Contact Angle ◽  
Silica Gel ◽  
Contact Angles ◽  
Dissipation Energy ◽  
Water Flows ◽  
Piston Cylinder ◽  
Pore Length ◽  
Spherical Silica ◽  
Extension Force

This paper presents on a new damping element called the colloidal damper which is used a principle of surface extension force in nano pore. The direction acting of the surface extension force of water in hydrophobic nano pore is different in pressurization and decompressurization processes [1,2]. This principle is applied to a damping element. The nano pore is constructed by silica gel. A silica gel ball of 100-200 micrometer dia. has many nano pores of 5-20 nanometer dia. in it [3,4]. The coated spherical silica gel and water are inserted in a piston - cylinder unit in order to work as a damper. If compression and decompression forces are added to the piston - cylinder unit (damper), water flows into and moves out the nano pore under balance of pressure. A contact angle of compression formed by the hydrophobic nano pore and water is larger than that of decompression. This difference of the contact angle produces a damping energy. In this paper, behavior of water in the pore of silica gel is investigated using the molecular dynamics. Dissipation energy of the colloidal damper is concerned with the contact angles of water in the pore. So the contact angles are calculated for changing parameters, i.e. size of the pore, length of the hydrophobic material, velocity (pressure) of water flows into the pore. Then these results are compared with the experimental ones.

Effect of Nanostructures and Wettability on the Instability of Thin Water Films on a Solid Surface: A Molecular Dynamics Study

2016 ◽  
Author(s):  
Liyong Sun ◽  
Jun Zhou ◽  
Phil Jones
Keyword(s):  
Molecular Dynamics ◽  
Contact Angle ◽  
Film Thickness ◽  
Energy Parameter ◽  
Gold Surface ◽  
Equilibrium Contact Angle ◽  
Droplet Spreading ◽  
Water Films ◽  
Critical Film Thickness ◽  
Solid Liquid

Molecular dynamics simulations are performed to investigate the stability of thin water films on square gold nanostructures of varying depth and wavelength. The critical film thickness of breakup is shown to increase linearly with nanostructure depth, and is not affected by nanostructure wavelength. In addition, the wettability of the gold surface is controlled from superhydrophilic to hydrophobic by altering the energy parameter of the solid-liquid potential, and the equilibrium contact angle for each energy parameter is calculated using a droplet spreading simulation. Four different energy parameters of the solid-liquid potential are investigated. The ratio of the energy parameter to the energy parameter of water and gold is 1, 0.5, 0.25 and 0.1. The case for ratio of 1 represents water on superhydrophilic gold surfaces. The relationship between the critical film thickness of breakup and the equilibrium contact angle is demonstrated. The results of the present work will provide guidelines for nanostructure design for controlling thin film stability.

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