Liquid–vapor interface of water–methanol mixture. I. Computer simulation

O between 7 and 24 GHz using a Fourier-transform microwave spectrometer. Because CH 3 OH and H 2 O are capable of both accepting and donating hydrogen bonds, there exists some question as to which donor-acceptor pairing of the molecules is the lowest energy form. This question is further emphasized by the ambiguity and variety present in previous experimental and computational results. Transitions arising from the methyl torsional A state were assigned in each of the studied isotopomers, and for the A and E states in , where the errors correspond to 1 uncertainties-are consistent with either conformation, the fit of the structure to the rotational constants demonstrates unambiguously that the lower-energy conformation formed in supersonically cooled molecular beams corresponds to a water-donor, methanol-acceptor complex. The results and implications for future work are also discussed in terms of the permutation-inversion theory presented by Hougen and Ohashi ͓J. Mol. Spectros. 159, 363 ͑1993͔͒.

Section: Structural Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Microwave rotation-tunneling spectroscopy of the water–methanol dimer: Direct structural proof for the strongest bound conformation

Stockman

Blake

Lovas

et al. 1997

“…The determination of the surface tension of water by computer simulation has been the subject of several studies. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] In the majority of these studies, a slab of liquid is placed in contact with vapor and the surface tension is computed from a mechanical route which requires the calculation of the pressure tensor. 39 A survey of the literature reveals that values of the surface tension from different authors differ in some cases considerably.…”

Section: Introductionmentioning

confidence: 99%

Surface tension of the most popular models of water by using the test-area simulation method

Vega

Miguel²

2007

696

105

699

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.

“…Most inhomogeneous studies of aqueous mixtures of alcohols tend to concentrate on liquid-vapor interfaces. 22,23 Some studies have looked at the structure of aqueous solutions of amphiphilic molecules like alcohols next to hydrophilic surfaces and the effect of this structuring on the properties of the system. 24,25 But structural studies at a hydrophobic surface has been mainly for pure water.…”

Section: Introductionmentioning

confidence: 99%

Hydrophobic and hydrophilic interactions in aqueous mixtures of alcohols at a hydrophobic surface

Ballal

Chapman

2013

Aqueous solutions of alcohols are interesting because of their anomalous behavior that is believed to be due to the molecular structuring of water and alcohol around each other in solution. The interfacial structuring and properties are significant for application in alcohol purification processes and biomolecular structure. Here we study aqueous mixtures of short alcohols (methanol, ethanol, 1-propanol, and 2-propanol) at a hydrophobic surface using interfacial statistical associating fluid theory which is a perturbation density functional theory. The addition of a small amount of alcohol decreases the interfacial tension of water drastically. This trend in interfacial tension can be explained by the structure of water and alcohol next to the surface. The hydrophobic group of an added alcohol preferentially goes to the surface preserving the structure of water in the bulk. For a given bulk alcohol concentration, water mixed with the different alcohols has different interfacial tensions with propanol having a lower interfacial tension than methanol and ethanol. 2-propanol is not as effective in decreasing the interfacial tension as 1-propanol because it partitions poorly to the surface due to its larger excluded volume. But for a given surface alcohol mole fraction, all the alcohol mixtures give similar values for interfacial tension. For separation of alcohol from water, methods that take advantage of the high surface mole fraction of alcohol have advantages compared to separation using the vapor in equilibrium with a water-alcohol liquid. © 2013 AIP Publishing LLC.