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 Kinetic pathways of water exchange in the first hydration shell of magnesium: Influence of water model and ionic force field

2021 ◽  
Author(s):  
Sebastian Falkner ◽  
Nadine Schwierz
Keyword(s):  
Force Field ◽  
Water Exchange ◽  
Force Fields ◽  
Hydration Shell ◽  
Water Model ◽  
Polarizable Force Fields ◽  
Ionic Force ◽  
Influence Of Water ◽  
Biomolecular Simulations ◽  
Dynamics Simulations

Water exchange between the first and second hydration shell is essential for the role of Mg2+ in biochemical processes. In order to provide microscopic insights into the exchange mechanism, we resolve the exchange pathways by all-atom molecular dynamics simulations and transition path sampling. Since the exchange kinetics relies on the choice of the water model and the ionic force field, we systematically investigate the influence of seven different polarizable and non-polarizable water and three different Mg2+ models. In all cases, water exchange can occur either via an indirect or direct mechanism (exchanging molecules occupy different/same position on water octahedron). In addition, the results reveal a crossover from an interchange dissociative (Id) to an associative (Ia) reaction mechanism dependent on the range of the Mg2+-water interaction potential of the respective force field. Standard non-polarizable force fields follow the Id mechanism in agreement with experimental results. By contrast, polarizable and long-ranged non-polarizable force fields follow the Ia mechanism. Our results provide a comprehensive view on the influence of the water model and ionic force field on the exchange dynamics and the foundation to assess the choice of the force field in biomolecular simulations.

scholarly journals Surface tension of O2-Ar, N2-Ar and O2-N2-Ar mixtures

2019 ◽  
pp. 21-27
Author(s):  
Mauricio García-Martínez ◽  
Benjamín Ibarra-Tandi ◽  
Daniel Porfirio Luis-Jiménez ◽  
Jorge López-Lemus
Keyword(s):  
Experimental Data ◽  
Surface Tension ◽  
Force Fields ◽  
Ternary Mixtures ◽  
Binary And Ternary Mixtures ◽  
Experimental Surface ◽  
Argon Mixture ◽  
Dynamics Simulations ◽  
Tension Curves ◽  
Good Agreement

The surface tension of some binary and ternary mixtures was calculated by means of molecular dynamics simulations in a canonical set. The analyzed mixtures were oxygen-argon, nitrogen-argon and oxygen-nitrogen-argon. The force field for argon was recalculated in order to reproduce the experimental surface tension. The corresponding force fields for O2 and N2 were taken from a previous work [Mol. Simul. 45 (2019) 958-966], where it was shown that such force fields reproduce the experimental surface tension curves, as pure fluids. The nitrogen-argon surface tension was calculated for several mole fractions of argon. The obtained curve was compared with those experimental data and a good agreement was found. The standard Lorentz-Berthelot combining rules were employed. For the oxygen-argon mixture it was necessary to modify the cross term of the combining rules in order to reproduce theoretical and experimental data. The surface tension of the ternary mixture was also estimated varying the mole fraction of argon at a certain concentration of oxygen and nitrogen, previously adjusted. Several temperatures were used in order to show a tendency mostly at relatively low temperatures. After comparing the available experimental data, which are scarce, a good agreement was observed.

scholarly journals Accurate Simulations of Lipid Monolayers Require a Water Model With Correct Surface Tension

2021 ◽  
Author(s):  
Carmelo Tempra ◽  
O.H. Samuli Ollila ◽  
Matti Javanainen
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Molecular Dynamics Simulations ◽  
Long Range ◽  
Van Der Waals ◽  
Water Model ◽  
Lipid Monolayers ◽  
Experimental Surface ◽  
Water Models ◽  
Dynamics Simulations

Lipid monolayers provide our lungs and eyes their functionality, and serve as proxy systems in biomembrane research. Therefore, lipid monolayers have been studied intensively also using molecular dynamics simulations, which are able to probe their lateral structure and interactions with, e.g., pharmaceuticals or nanoparticles. However, such simulations have struggled in describing the forces at the air–water interface. Particularly the surface tension of water and long-range van der Waals interactions have been considered critical, but their importance in monolayer simulations has been evaluated only separately. Here we combine the recent C36/LJ-PME lipid force field that in- cludes long-range van der Waals forces with water models that reproduce experimental surface tensions to elucidate the importance of these contributions in monolayer simulations. Our results suggest that a water model with correct surface tension is necessary to reproduce experimental surface pressure–area isotherms and monolayer phase behavior, while standard cutoff-based CHARMM36 lipid model with the 4-point OPC water model still provides the best agreement with experiments. Our results emphasize the importance of using high quality water models in applications and parameter development in molecular dynamics simulations of biomolecules.

scholarly journals Hydrophobic association and solvation of neopentane in Urea, TMAO and Urea-TMAO solution

2021 ◽  
Author(s):  
Timir Hajari ◽  
Mayank Dixit ◽  
Hari O. S. Yadav
Keyword(s):  
Interaction Energy ◽  
Force Fields ◽  
Water Solution ◽  
Pure Water ◽  
Hydrophobic Association ◽  
Urea Solution ◽  
Detailed Knowledge ◽  
Cavity Formation ◽  
Neat Water ◽  
Dynamics Simulations

A detailed knowledge on hydrophobic association and solvation is crucial in understanding the con-formational stability of proteins and polymers in osmolyte solutions. Using Molecular Dynamics simulations, we found the hydrophobic association using neopentane molecules is greater in mixed urea-TMAO-water solution in comparison to that in 8 M urea solution, in 4 M TMAO solution and in neat water. The neopentane association in urea solution is greater than that in TMAO solution or neat water. We find the association is even less in TMAO solution than pure water. From free ener-gy calculations, it is revealed that the neopentane sized cavity creation in mixed urea-TMAO-water is most unfavorable and that causes the highest hydrophobic association. The cavity formation in urea solution is either more unfavorable or comparable to that in TMAO solution. Importantly, it is found that the population of neopentane-neopentane contact pair and the free energy contribution for cavity formation step in TMAO solution are very sensitive towards the choice of TMAO force-fields. A careful construction of TMAO force-fields is important for studying hydrophobic associa-tion. Interestingly it is observed that the total solute-solvent dispersion interaction energy contribu-tion is always most favorable in mixed urea-TMAO-water. The magnitude of this interaction energy is greater in urea solution relative to TMAO solution for two different force-fields of TMAO, whereas the lowest value is obtained in pure water. It is revealed that the extent of the overall hy-drophobic association in osmolyte solutions is mainly governed by the cavity creation step and it nullifies the contribution comes from the solute-solvent interaction contribution.

Dependence of Surface Tension on Surface Concentration in Ionic Surfactant Solutions and Influences of Supporting Electrolyte Therein

2019 ◽  
Vol 56 (6) ◽  
pp. 484-489
Author(s):  
Chuangye Wang ◽  
Feng Liu ◽  
Hongxia Yang ◽  
Harald Morgner ◽  
Longli Zhang ◽  
...  
Keyword(s):  
Surface Tension ◽  
Supporting Electrolyte ◽  
Surface Concentration ◽  
Ionic Surfactant ◽  
Surfactant Solutions

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.

A Liquid Water Model That Explains the Variation of Surface Tension of Water with Temperaure

2001 ◽  
Vol 40 (Part 1, No. 3A) ◽  
pp. 1467-1471 ◽  
Author(s):  
Arshad Khan ◽  
M. Rezwan Khan ◽  
M. Ferdouse Khan ◽  
Fahima Khanam
Keyword(s):  
Surface Tension ◽  
Liquid Water ◽  
Water Model

The kinetics of the surface tension of micellar surfactant solutions

1991 ◽  
Vol 60 ◽  
pp. 235-261 ◽  
Author(s):  
C.D. Dushkin ◽  
I.B. Ivanov ◽  
P.A. Kralchevsky
Keyword(s):  
Surface Tension ◽  
Surfactant Solutions ◽  
Micellar Surfactant Solutions ◽  
Kinetics Of
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