The surface tension of water calculated from a random network model (original) (raw)
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Microscopic Origin of the Surface Tension Anomaly of Water
Langmuir, 2014
We investigate the hydrogen bonding percolation threshold of water molecules at the surface of the liquid-vapor interface. We show that the percolation temperature agrees within statistical accuracy with the high-temperature inflection point of the water surface tension. We associate the origin of this surface tension anomaly of water with the sudden breakup of the hydrogen bonding network in the interfacial molecular layer.
A Simple Statistical Mechanical Model of Water
We introduce a statistical mechanical model for the physical properties of water. Each water molecule is a two-dimensional disk with three radial hydrogen-bonding arms. Energetic interactions are based on water triplets, a central water molecule interacting with two neighbors via hydrogen bonds, van der Waals attractions, and steric repulsions. Interactions with more distant molecules are treated in a mean-field way. Each molecular triplet can be in one of three energy levels: cage-like hydrogen-bonded structures, denser nonbonded structures, and expanded structures with no near-neighbor interactions. The model predicts water's thermodynamic anomalies, including maxima in density, minima in isothermal compressibility and heat capacity, and expansion upon freezing at low pressure. It predicts the main features of water's phase diagram, including multiple crystalline phases and the proposed liquid-liquid transition in supercooled water. Also, it captures qualitatively the fragile-to-strong transition in the liquid's temperature-dependent relaxation processes. This model is intended to give simple insights into the microscopic origins of water's distinctive physical properties.
Surface tension of the most popular models of water by using the test-area simulation method
The Journal of Chemical Physics, 2007
We consider the calculation of the surface tension from simulations of several models of water, such as the traditional TIP3P, SPC, SPC/E, and TIP4P models, and the new generation of TIP4P-like models including the TIP4P/Ew, TIP4P/Ice, and TIP4P/2005. We employ a thermodynamic route proposed by Gloor et al. ͓J. Chem. Phys. 123, 134703 ͑2005͔͒ to determine the surface tension that involves the estimate of the change in free energy associated with a small change in the interfacial area at constant volume. The values of the surface tension computed from this test-area method are found to be fully consistent with those obtained from the standard mechanical route, which is based on the evaluation of the components of the pressure tensor. We find that most models do not reproduce quantitatively the experimental values of the surface tension of water. The best description of the surface tension is given by those models that provide a better description of the vapor-liquid coexistence curve. The values of the surface tension for the SPC/E and TIP4P/Ew models are found to be in reasonably good agreement with the experimental values. From the present investigation, we conclude that the TIP4P/2005 model is able to accurately describe the surface tension of water over the whole range of temperatures from the triple point to the critical temperature. We also conclude that the test area is an appropriate methodological choice for the calculation of the surface tension not only for simple fluids, but also for complex molecular polar fluids, as is the case of water.
Molecular dynamics simulation of the orthobaric densities and surface tension of water
The Journal of chemical …, 1995
Molecular dynamics simulations have been performed to study the liquid-vapor equilibrium of water as a function of temperature. The orthobaric densities and the surface tension of water are reported for temperatures from 316 K until 573 K. The extended simple point charge ͑SPC/E͒ interaction potential for water molecules is used with full Ewald summation. The normal and tangential components of the pressure tensor were calculated and are presented at 328 K. The nature of the long-range contribution to the surface tension has been studied in detail. At 328 K the calculated surface tension is 66.0Ϯ3.0 mN m Ϫ1 in comparison with the experimental value of 67 mN m Ϫ1. The simulated surface tensions between 316 K and 573 K are in good agreement with experiment. The orthobaric densities are in better agreement with experimental values than those obtained from the Gibbs ensemble calculation for the SPC model of water.
The Dynamic Surface Tension of Water
The journal of physical chemistry letters, 2017
The surface tension of water is an important parameter for many biological or industrial processes, and roughly a factor of 3 higher than that of nonpolar liquids such as oils, which is usually attributed to hydrogen bonding and dipolar interactions. Here we show by studying the formation of water drops that the surface tension of a freshly created water surface is even higher (∼90 mN m(-1)) than under equilibrium conditions (∼72 mN m(-1)) with a relaxation process occurring on a long time scale (∼1 ms). Dynamic adsorption effects of protons or hydroxides may be at the origin of this dynamic surface tension. However, changing the pH does not significantly change the dynamic surface tension. It also seems unlikely that hydrogen bonding or dipole orientation effects play any role at the relatively long time scale probed in the experiments.
The Journal of Chemical Physics, 2010
A water molecule in the vicinity of a hydrophobic surface forms fewer hydrogen bonds than a bulk molecule because the surface restricts the space available for other water molecules necessary for its hydrogen-bonding. In this vicinity, the number of hydrogen bonds per water molecule depends on its distance to the surface. Considering the number of hydrogen bonds per bulk water molecule ͑available experimentally͒ as the only reference quantity, we propose an improved probabilistic approach to water hydrogen-bonding that allows one to obtain an analytic expression for this dependence. ͑The original version of this approach ͓Y. S. Djikaev and E. Ruckenstein, J. Chem. Phys. 130, 124713 ͑2009͔͒ provides the number of hydrogen bonds per water molecule in the vicinity of a hydrophobic surface as an average over all possible locations and orientations of the molecule.͒ This function ͑the number of hydrogen bonds per water molecule versus its distance to a hydrophobic surface͒ can be used to develop analytic models for the effect of hydrogen-bonding on the hydration of hydrophobic particles and their solvent-mediated interaction. Presenting a model for the latter, we also examine the temperature effect on the solvent-mediated interaction of two parallel hydrophobic plates.
The Journal of chemical physics, 2014
The percolation temperature of the lateral hydrogen bonding network of the molecules at the free water surface is determined by means of molecular dynamics computer simulation and identification of the truly interfacial molecules analysis for six different water models, including three, four, and five site ones. The results reveal that the lateral percolation temperature coincides with the point where the temperature derivative of the surface tension has a minimum. Hence, the anomalous temperature dependence of the water surface tension is explained by this percolation transition. It is also found that the hydrogen bonding structure of the water surface is largely model-independent at the percolation threshold; the molecules have, on average, 1.90 ± 0.07 hydrogen bonded surface neighbors. The distribution of the molecules according to the number of their hydrogen bonded neighbors at the percolation threshold also agrees very well for all the water models considered. Hydrogen bonding...
Surface tension of water–alcohol mixtures from Monte Carlo simulations
The Journal of Chemical Physics, 2011
Monte Carlo simulations are reported to predict the dependence of the surface tension of wateralcohol mixtures on the alcohol concentration. Alcohols are modeled using the anisotropic united atom model recently extended to alcohol molecules. The molecular simulations show a good agreement between the experimental and calculated surface tensions for the water-methanol and waterpropanol mixtures. This good agreement with experiments is also established through the comparison of the excess surface tensions. A molecular description of the mixture in terms of density profiles and hydrogen bond profiles is used to interpret the decrease of the surface tension with the alcohol concentration and alcohol chain length.
The Journal of Physical Chemistry Letters, 2011
H ydrogen bonding constitutes a key element of many physical, chemical, and biological phenomena of utmost scientific interest. 1À7 It is believed to play a crucial role in the hydration of hydrophobic particles and their solvent-mediated interactions in aqueous solutions (hydrophobic interactions). Various mechanisms have been suggested to understand hydrophobicity at a fundamental level 8À12 and develop a general theory thereof. Although many controversies remain, 13,14 there seems to be a convergence of views on its dependence on the length scales of hydrophobic particles involved.