Effect of Cutoff Radius on the Surface Tension of Nanoscale Bubbles

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
Ian A. Cosden ◽  
Jennifer R. Lukes
Keyword(s):  
Surface Tension ◽  
Strong Dependence ◽  
Pressure Profile ◽  
System Size ◽  
Homogeneous Fluid ◽  
Density Profiles ◽  
Curvature Effects ◽  
Cutoff Radius ◽  
Dynamics Simulations ◽  
Small Bubbles

Molecular dynamics simulations are performed to calculate the surface tension of bubbles formed in a metastable Lennard–Jones (LJ) argon fluid. The calculated normal and transverse pressure components are used to compute a surface tension which is compared to the surface tension computed from the Young–Laplace equation. Curvature effects on surface tension are investigated by performing various sized simulations ranging from 6912 to 256,000 LJ particles. The computed surface tension values differ depending on the calculation method for the smaller systems studied but the methods converge as the system size increases. Surface tension calculations on small bubbles may not be appropriate since the liquid farthest from the interface has yet to achieve the pressure profile of a homogeneous fluid. Density profiles, pressures, and calculated surface tensions are shown to have a strong dependence on the choice of the interaction cutoff radius. A cutoff radius of 8σ, significantly larger than that commonly used in the literature, is recommended for accurate calculations in liquid–vapor systems.

The Surface Tension of Nanobubbles and the Effect of the Potential Cutoff Radius

2010 ◽  
Author(s):  
Ian A. Cosden ◽  
Jennifer R. Lukes
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Strong Dependence ◽  
Md Simulations ◽  
Density Profiles ◽  
Curvature Effects ◽  
Lennard Jones ◽  
Transverse Pressure ◽  
Cutoff Radius ◽  
Interaction Cutoff

Molecular dynamics (MD) simulations are carried out to calculate the surface tension of bubbles formed in a metastable Lennard-Jones (LJ) fluid. The calculated normal and transverse pressure components are used to compute a surface tension which is compared to the surface tension computed from the Young-Laplace equation. Curvature effects on surface tension are investigated by performing various sized simulations ranging from 6,912 to 256,000 LJ particles. Density profiles, pressures, and calculated surface tension are shown to have a strong dependence on the choice of the interaction cutoff radius. A cutoff radius of 8σ, significantly larger than that commonly used in the literature, is recommended for accurate calculations in liquid-vapor systems.

scholarly journals Role of the Counterions in the Surface Tension of Aqueous Surfactant Solutions. A Computer Simulation Study of Alkali Dodecyl Sulfate Systems

2020 ◽  
Vol 4 (2) ◽  
pp. 15 ◽  
Author(s):  
György Hantal ◽  
Marcello Sega ◽  
George Horvai ◽  
Pál Jedlovszky
Keyword(s):  
Surface Tension ◽  
Force Fields ◽  
Surface Concentration ◽  
Pressure Profile ◽  
Water Model ◽  
Model Combination ◽  
Neat Water ◽  
Surfactant Solutions ◽  
Dodecyl Sulfate ◽  
Dynamics Simulations

We have investigated the surface tension contributions of the counterions, surfactant headgroups and tails, and water molecules in aqueous alkali dodecyl sulfate (DS) solutions close to the saturated surface concentration by analyzing the lateral pressure profile contribution of these components using molecular dynamics simulations. For this purpose, we have used the combination of two popular force fields, namely KBFF for the counterions and GROMOS96 for the surfactant, which are both parameterized for the SPC/E water model. Except for the system containing Na+ counterions, the surface tension of the surfactant solutions has turned out to be larger rather than smaller than that of neat water, showing a severe shortcoming of the combination of the two force fields. We have traced back this failure of the potential model combination to the unphysically strong attraction of the KBFF counterions, except for Na+, to the anionic head of the surfactants. Despite this failure of the model, we have observed a clear relation between the soft/hard character (in the sense of the Hofmeister series) and the surface tension contribution of the counterions, which, given the above limitations of the model, can only be regarded as an indicative result. We emphasize that the obtained results, although in a twisted way, clearly stress the crucial role the counterions of ionic surfactants play in determining the surface tension of the aqueous surfactant solutions.

scholarly journals Thermal Properties of Yttrium Aluminum Garnett From Molecular Dynamics Simulations

2011 ◽  
Author(s):  
Majid S. al-Dosari ◽  
D. G. Walker
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Specific Heat ◽  
Molecular Dynamics Simulations ◽  
Yttrium Aluminum Garnet ◽  
System Size ◽  
Yttrium Aluminum ◽  
Dynamics Simulations

Yttrium Aluminum Garnet (YAG, Y3Al5O12) and its varieties have applications in thermographic phosphors, lasing mediums, and thermal barriers. In this work, thermal properties of crystalline YAG where aluminum atoms are substituted with gallium atoms (Y3(Al1−xGax)5O12) are explored with molecular dynamics simulations. For YAG at 300K, the simulations gave values close to experimental values for constant-pressure specific heat, thermal expansion, and bulk thermal conductivity. For various values of x, the simulations predicted no change in thermal expansion, an increase in specific heat, and a decrease in thermal conductivity for x = 50%. Furthermore, the simulations predicted a decrease in thermal conductivity with decreasing system size.

scholarly journals Interface Characteristics of Neat Melts and Binary Mixtures of Polyethylenes from Atomistic Molecular Dynamics Simulations

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1059
Author(s):  
Sanghun Lee ◽  
Curtis W. Frank ◽  
Do Y. Yoon
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Molecular Dynamics Simulations ◽  
Binary Mixtures ◽  
Surface Segregation ◽  
Surface Region ◽  
Polymer Chains ◽  
Methyl Groups ◽  
Free Standing ◽  
Dynamics Simulations

Molecular dynamics simulations of free-standing thin films of neat melts of polyethylene (PE) chains up to C150H302 and their binary mixtures with n-C13H28 are performed employing a united atom model. We estimate the surface tension values of PE melts from the atomic virial tensor over a range of temperatures, which are in good agreement with experimental results. Compared with short n-alkane systems, there is an enhanced surface segregation of methyl chain ends in longer PE chains. Moreover, the methyl groups become more segregated in the surface region with decreasing temperature, leading to the conclusion that the surface-segregation of methyl chain ends mainly arises from the enthalpic origin attributed to the lower cohesive energy density of terminal methyl groups. In the mixtures of two different chain lengths, the shorter chains are more likely to be found in the surface region, and this molecular segregation in moderately asymmetric mixtures in the chain length (C13H28 + C44H90) is dominated by the enthalpic effect of methyl chain ends. Such molecular segregation is further enhanced and dominated by the entropic effect of conformational constraints in the surface for the highly asymmetric mixtures containing long polymer chains (C13H28 + C150H3020). The estimated surface tension values of the mixtures are consistent with the observed molecular segregation characteristics. Despite this molecular segregation, the normalized density of methyl chain ends of the longer chain is more strongly enhanced, as compared with the all-segment density of the longer chain itself, in the surface region of melt mixtures. In addition, the molecular segregation results in higher order parameter of the shorter-chain segments at the surface and deeper persistence of surface-induced segmental order into the film for the longer chains, as compared with those in neat melt films.

Molecular Dynamics Study of Anatase TiO2 Nanoparticles in Water and Vacuum Environments

2012 ◽  
Author(s):  
George Okeke ◽  
Robert B. Hammond ◽  
S. Joseph Antony
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Surface Energy ◽  
Tio2 Nanoparticles ◽  
Anatase Tio2 ◽  
Particle Sizes ◽  
Metallic Oxides ◽  
Wide Range ◽  
Enhanced Properties ◽  
Dynamics Simulations

Nanoparticles are nanometer sized metallic oxides which possess enhanced properties that are desirable to a wide range of industries. In this study, we investigate structural and surface properties of anatase TiO2 nanoparticles in vacuum and water environments using molecular dynamics simulations. The particle sizes ranged from 2 to 6 nm and simulations were performed at 300 K. Surface energy of the particles in vacuum was seen to be higher than that of the particles in water by about 100% for the smaller particles (i.e. 2 and 3nm) and about 60% for the larger particles (i.e. 4 to 6 nm). Surface energy of the particles in both environments, is seen to increase to a maximum (optimum value) as the particle size increases after which no further significant increase is observed. In vacuum, studies carried out at temperatures ranging from 300–2500 K showed a high dependence of surface energy on temperature. The estimated surface tension of water is seen to agree quite well with that of experiments.

scholarly journals Arrest of the flow of wet granular matter

2013 ◽  
Vol 738 ◽  
pp. 407-422 ◽  
Author(s):  
Klaus Roeller ◽  
Johannes Blaschke ◽  
Stephan Herminghaus ◽  
Jürgen Vollmer
Keyword(s):  
External Force ◽  
Granular Matter ◽  
Three Dimensional ◽  
Vertical Direction ◽  
System Size ◽  
Critical Force ◽  
Flow Profile ◽  
Universal Method ◽  
Dynamics Simulations ◽  
Energy Dissipated

AbstractWe study the arrest of three-dimensional flow of wet granular matter subject to a sinusoidal external force and a gravitational field confining the flow in the vertical direction. The minimal strength of the external force that is required to keep the system in motion, i.e. the critical force, is determined by considering the balance of injected and dissipated power. This provides a prediction whose quality is demonstrated by a data collapse for an extensive set of event-driven molecular-dynamics simulations where we varied the system size, particle number, the energy dissipated upon rupturing capillary bridges, and the bridge length at which rupture occurs. The same approach also works for systems that are kept at a fixed density by confining walls. In both cases, this universal method provides the critical force irrespective of the flow profile, and without specifying the hydrodynamic equations.

Molecular Dynamics Simulations and Theory of Interfaces of Oligomers

1992 ◽  
Vol 291 ◽  
Author(s):  
Jonathan G. Harris ◽  
Yantse Wang
Keyword(s):  
Surface Tension ◽  
Glassy State ◽  
Surface Force ◽  
Molecular Motions ◽  
Molecular Fluids ◽  
Force Microscopy ◽  
Atomic Force ◽  
Branched Alkanes ◽  
Dynamics Simulations ◽  
Solvation Forces

ABSTRACTThese proceedings summarize recent work in our group studying the structure of interfaces involving molecular fluids. Two types of systems are discussed. First, we summarize simulations of the structure and surface tension of liquid-vapor interfaces of the alkanes eicosane and decane. Then, we describe the results of simulations of the confined films studied in surface force apparatus and atomic force microscopy experiments. Our simulations show that in both films of normal and branched alkanes, the formation of a layered structure is observed. The branching inhibits this layering, especially in the narrowest pores. In addition an examination of the molecular motions indicates that a transition to a solid or glassy state is not a prerequisite for layering or oscillating solvation forces.

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