Project number:

PROJECT TITLE

Structural and transport properties of aqueous solutions

PROJECT SUPERVISOR

Name: Josep BONET AVALOS

e-mail:
josep.bonet@urv.net
Telephone: + 34 977 55 96 45



DESCRIPTION

 


Overview:

Despite its apparent simplicity, water is one of the most fascinating substances in nature, and its behaviour and properties are far from being completely understood. We can mention, for instance, the maximum in the density at 4ºC (at 1 atm.), its ability in dissolving electrolyte substances (salts) at subcritical conditions and precipitate them at supercritical (above 376 ºC at different densities), the so-called hydrophobic effect, or even the possible existence of two types of liquids in subcooled pure water, a heavy and a light water. Aqueous mixtures of associating fluids also present anomalous non-ideal effects, as the maximum of the viscosity, higher than that of the pure components (water and methanol, for instance), and many other structural effects in the mixtures related to the microscopic distribution of the substances. There are many properties with similar anomalous behaviours the origin of which is related to the particular molecular structure of water and the existence of strong, short-range, directional hydrogen bond interactions.

This project is oriented at the application of molecular dynamics techniques (and computer simulation techniques, in general) to the study of the relationship between the microscopic structural behaviour of aqueous solutions and their macroscopic equilibrium and transport properties, with the ultimate goal of a better understanding of the microscopic reasons of such strange behaviour [1,2,3,4].

Background and State of the Art:

During the past years a great effort has been made to establish the liaison between the particular microscopic structure of water and its macroscopic properties, from experimental observations, molecular simulations as well as theoretical calculations from simplified models [5, 6, 7, 8]. Due to its practical interest, there is also a large effort in the development of models for water molecules that could permit an accurate prediction of the macroscopic properties in molecular simulations, that will ultimately be of interest for industrial applications (for instance the SPC/E [9] and the DEC [10] models). The current investigations are oriented to the study of several aspects that can give the clue for an understanding of the behaviour of water mixtures: the life-time of the hydrogen bonds, the persistence of the three-dimensional network of water molecules and its effect on the macroscopic properties near the critical point, the hydrophobic effect, as well as in the impact of these structures in the transport properties such as diffusion, viscosity and thermal conductivity, all of them of great applied interest. The group has experience in the use of the needed tools to attempt this study, and significant technical developments have been recently carried out [11]. The contribution of senior researchers as well as experienced postdoctoral students, together with a positive environment strongly favours the positive outcome of this investigation.

 

 

 

 

 

 

Project Contribution and Methodology:

At present, research based on molecular simulations of industrially relevant substances is being carried out in the Department of Chemical Engineering at the URV. The most relevant topics involve i) phase equilibria of mixtures and ii) transport properties also of mixtures. The present project is mainly concerned with the second point, although will strongly entangle with the research currently carried out relative to the first point.

In recent years we have build experience in the use of equilibrium as well as non-equilibrium for the determination of macroscopic properties by means of molecular dynamics simulations, in the framework of a long lasting collaboration with the Université de Paris Sud and the Institut Français du Pétrole, as well as with the group Complex Systems of our department.

The methodology to be employed is the use of the existing Molecular Dynamics codes for equilibrium as well as non-equilibrium situations. This will require familiarisation with the codes, although some code development as well as molecular model development could be required. Some theoretical work on simple models of the studied systems will be also tentatively undertaken, aiming at clarifying and complementing the numerical results obtained.

The ideal candidate:

It is essential for the success of the candidate to show aptitude for the abstract reasoning, since the most of the work will involve computer implementation of the developed algorithms as well as analysis of results. Thus, graduates of Engineering and Physics have the appropriate background, although Chemistry graduates can also do well if they do not fear formal work.

Finishing this project:

At the end of the PhD the student will have acquired expertise in the modelling of mixtures of interest from a microscopic point of view. Such a formation will be suitable to start independent work in many Chemical Engineering departments at universities. In addition, the applied side of the research will make the student an excellent candidate to be incorporated in many research and development groups of industries related petrochemical derivatives, etc., as the success of some of our former students may witness.

References:

[1] Dynamic and structural behavior of different rigid non-polarizable modes of water, C. Nieto-Draghi, B. Rousseau and J. Bonet Avalos, J. Chem. Phys. 118, 7954, (2003)
[2] Transport properties of aqueous solutions of DMSO,C. Nieto-Draghi, B. Rousseau and J. Bonet Avalos, J. Chem. Phys.
119 4782, (2003)
[3]  C. Nieto-Draghi, J. Bonet Avalos and B. Rousseau, Computing the Soret coefficient in aqueous mixtures using boundary driven nonequilibrium molecular dynamics, Journal of Chemical Physics, 122 (2005), 114503
[4] C. Nieto-Draghi, J. Bonet Avalos, O. Contreras, Ph. Ungerer, and J. Ridard, Dynamical and structural properties of benzene in supercritical water. Journal of Chemical Physics, 121 (2004), 10566 (pdf)
[5] Phase Diagram of Water from Computer Simulation, E. Sanz, C. Vega, J. L. F. Abascal, and L. G. MacDowell, Phys. Rev. Lett. 92, 255701, (2004)
[6] J. R. Errington and P. Debenedetti, Nature 409, p318 (2001).
[7] H. Tanaka, J. Phys.: Condens. Matter 11, L159 (1999).
[8] A. K. Soper, Chem. Phys. 258, p121 (2000).
[9] H. J. C. Berendsen, J. R. Grigera, and T. P. Straasma, J. Phys. Chem. 91, p6269 (1987).
[10] B. Guillot and Y. Guissani, J. Chem. Phys. 114, p6720 (2001).
[11] Histogram Reweighting Method for Dynamic Properties, C. Nieto-Draghi, J. Pérez-Pellitero and J. Bonet Avalos, Phys. Rev. Lett. 95, 040603, (2005)


(c) 2003, Doctoral Studies in Chemical and Process Engineering, Universitat Rovira i Virgili