Simple and complex models of aqueous solutions: The effect of nonadditive interactions
Principal researcher: I. Nezbeda
[Supported by the Grant Agency of the Academy of Sciences (2008-2012)]
(back-to-list-of-projects)
SUMMARY
Aqueous solutions of lower alcohols and typical volatile organic compounds, represented by
nonadditive pseudo hard bodies and realistic both nonpolarizable and polarizable models, will be
studied by computer simulations at both simple and complex levels. The simple models serve as a
basis for development of a (perturbation) theory of these fluids and their mixtures. The simulations
of the complex models will investigate the role of nonadditive interactions, implemented by
polarizability and/or modified cross interactions. The emphasis on nonadditive models and
corresponding theory is dictated by the failure of standard, additive approaches to reliably describe
the experimental data over the entire concentration range. The development of methodology of
computer simulations, which is an integral part of this project, includes efficient methods for
simulations of polarizable fluids and their generalization for determination of phase equilibria.
Thermophysical properties of practically important fluids and fluid mixtures at superambient conditions from molecular-based theory and experiment.
Principal researcher: K. Aim
Co-researcher: T. Boublik, I. Nezbeda, J. E. Purkinje
University, Usti n. Lab.
[Supported by the Grant Agency of the
Academy of Sciences (2007-2011)]
(back-to-list-of-projects)
SUMMARY
The aim of the research is to develop
accurate workable equations for practical applications in calculating
the thermophysical properties of real fluids constituted of
non-spherical, polar, and associating molecules and for their mixtures,
based on utilizing the frontier molecular theories of fluids supported
by up-to-date computer molecular simulations. Two main lines of the
research shall be pursued, namely (i) the development of equations of
state for different classes of fluids, based on the primitive model
reference fluids, and (ii) the improvement of the perturbation theory
and of the virial expansion for the model fluid of convex molecules
interacting via the Kihara surface-to-surface potential. The project
involves also experimental determination of thermodynamic properties
for selected systems required to verify the approach. The resulting
relations should be formulated in closed forms and should make it
possible to calculate the thermophysical properties of fluid mixture
systems for process design with sufficient accuracy over extended
ranges of state conditions.
Application of advanced simulation methods for studying the structure, physico-chemical properties, and preparation of composites and nanomaterials.
Principal researcher: I. Nezbeda
Co-researcher: S. Novak, J. E. Purkinje University, Usti n.
Lab.
[Supported by the "Information Society Programme" (2004-2008)]
(back-to-list-of-projects)
SUMMARY
The project deals with the development and
subsequent applications of new methods and algoritms for computer
modeling and molecular simulations in material research, particularly
for utilization of nanomaterials as nanoreactors, and for materials with
the complex surface and/or bulk structure. The target of the research
are (1) morphological properties of materials and their relation to
other physico-chemical properties, and (2) physico-chemical processes at
or near the surface. The goal of the project is the development of
molecular simulation methodology for chemically reacting systems in
nanopores, and development of morphological analysis methodology for
optimization of the laser welding technology. The applied methodology
starts with the development and optimization of appropriate models and
algorithms that are followed by the investigation of the models and
assessment of the results and ends with applications of the models to
selected industrial problems.
Metastable water and steam
Principal researcher: J. Hruby, Inst. of Thermomechanics, Acad. Sci.
Co-researchers: V. Zdimal, I. Nezbeda, Inst. Chem. Process Fund.,
Acad. Sci., Prague
P. Demo, Institute of Physics, Acad. Sci., Prague
K. Studenovsky, Czech Technical University, Prague
R. Mares, West Bohemia University, Plzen
[Supported by the Grant Agency of the Czech Republic (2005-2007)]
(back-to-list-of-projects)
SUMMARY
The properties of water and steam are known to a great detail. However,
little is known about the metastable states: supercooled water,
superheated and stretched water, supersaturated steam, and about
homogeneous nucleation. Metastable states, followed by nucleation, exist
in a number of technological applications (energy production, food
industry) and processes in the nature (atmospheric, geological, and
biological). We suggest sophisticated experiments to obtain missing
engineering data and to answer fundamental problems. A device will be
developed for measurement of the surface tension of supercooled water;
the experiments should confirm or disprove its anomalous temperature
dependency and the hypothesized denser surface layer. Measurements of
nucleation of supercooled and stable droplets using a shock tube and
diffusion cloud chamber in an extended temperature range will be used to
determine the size and formation energy of critical clusters and to
deduce the microscopic surface tension. Factors influencing the
supercooling limit and the kinetics of freezing will be studied. Water
clusters, bulk supercooled liquid and its surface will be simulated
using Monte Carlo method and density functional theory. From the
computed formation energies the size-dependency of the surface tension
will be obtained. Based on both experimental and simulation results,
semi-phenomenological analytical models of metastable water and
nucleation will be developed, enabling engineering application. The team
collaborates with renowned laboratories abroad.
General equations of state of fluids from molecular principles and their application to thermophysical properties of fluid mixtures
Principal researcher: I. Nezbeda
[Supported by the Grant Agency of the Academy of Sciences
(2003-2006)]
(back-to-list-of-projects)
SUMMARY
Using realistic (transferable) site-site potentials and latest
results of molecular theories of fluids, equations of state for
fluids will be developed in a uniform form regardless of details of
intermolecular interactions. The equations have the form of a
perturbed equation about a suitable short-range reference. The used
perturbation expansion is based on results of recent investigations
of the effect of long-range interactions on the properties of
fluids. For the description of the reference, simple short-range
(primitive) models that account both for the shape and size of
molecules and short-range effects of electrostatic interactions will
be developed for selected classes of fluids and their
appropriateness and applicability will be examined by computer
simulations and theory. The application part will focus on mixtures
encountering in or considered for environmentally friendly
technologies. Particularly, on mixtures containing water, carbon
dioxide, and hydrocarbons.
Molecular model of aqueous solutions of electrolytes and its application
Principal researcher: I. Nezbeda
[Supported by the Grant Agency of the Czech Republic (2002-2004)]
(back-to-list-of-projects)
SUMMARY
As a step beyond the McMillan-Mayer concept, the project aims at an
application and further development of a new molecular model of aqueous
solutions of electrolytes at the Born-Oppenheimer level. The model incorporates
the recently developed primitive model of water and a specific form of
the ion-solvent interaction. The main goals are both theoretical and practical
and may be summarized as follows:(1) Using the recent computer simulation
results for infinitely dilute solutions, to derive by means of theory analytic
expressions for the limiting activity coefficients and apply them to real
dilute aqueous solutions of electrolytes of practical interest. (2) To
investigate further the validity of the concept of the short-range ion-solvent
interactions for dilute solutions and the dependence of various phenomena
(as e.g. structure breaking and structure enhancement) on the strength
of the ion-water interaction and on the size of ions. (3) To extend the
concept of the model with short-range interactions to solutions at medium
and high concentrations and to investigate, primarily by means of computer
simulations, the limits of its validity, especially with respect to ion
pairing and the concentration dependence of the thermodynamic functions.
(4) To develop a theory for the model solutions with short-range interactions
as a zeroth-order approximation of the properties of real solutions at
finite concentrations.
Molecular-based prediction of solubility in bulk and confined systems
Principal researchers: W.R. Smith and I. Nezbeda
[Supported by NATO Science Programme (2002-2003)]
(back-to-list-of-projects)
SUMMARY
The goal of this project is to develop molecular-based methods for the
prediction of solubility of compounds in several types of solvents. The
molecular-based methods will include the development and application of
novel computer simulation techniques and integral equation methods.
These methods will be applied to organic and organo-metallic solutes in
supercritical solvents such as CO2 and water, and in subcritical
solvents such as octanol and water. The solvents considered include
both bulk systems and model molecularly-confined systems. The latter
are first-approximation models of real porous media.
SUMMARY
The aim of the proposed project is a study of the fundamental problem
of the existence (or non-existence) of purely entropically driven phase
equilibria between two isotropic fluid phases in binary mixtures of highly
asymmetric additive hard spheres. Both true binary mixtures and one-component
systems (made up of large spheres interacting via an effective depletion
potential) will be investigated. Gibbs ensemble and integral equation methods
will be used. An attempt to develop an equation of state will be made and
the global phase diagram will be determined.
SUMMARY
The primary goal of the project is to develop a molecular theory of
associating fluids by means of a perturbation theory and recently developed
primitive models. The crucial step of the suggested method is to find a
mapping of the properties of short-ranged reference systems onto those
of the associated primitive models. All classes of associated fluids will
be considered with emphasis on supercritical aqueous solutions and mixtures
of water and alcohols. Specific goals which the project will pursue are
as follows:
1. To develop an analytic equation of state and expressions for other
thermodynamic properties in the form of a perturbed primitive model.
2. Using the results, to investigate supercritical aqueous mixtures,
and to systematically study mixtures of water and alcohols with n-alkanes,
and mixtures of water and alcohols.
3. Special attention will be paid to liquid-liquid immiscibilities
and occurrence of azeotropic phenomena and their prediction for homologous
series.
SUMMARY
The main goal of this project is to develop a theoretical method capable
to describe accurately the thermodynamic properties of the exp-6 fluids
and their mixtures, and to derive in a closed analytic form an equation
of state and apply it to analyze and predict the behavior of mixtures encountered
in geochemical applications; it means, compressed mixtures at temperatures
ranging from the critical temperature of water to about 1200C and at pressures
up to 5Gbar, and containing hydrogen, nitrogen, oxygen, water, carbon dioxide,
and carbon monoxide. The scope of the project covers both the extensive
simulations of the mixtures and wide range of theoretical methods which
include integral equation and perturbation theories, and recently proposed
volume-explicit approach for developing an equation of state. Specifically,
the individual steps of the project are as follows:
1. To develop exp-6 potential models (simple spherical and site-site)
for the substances of interest;
2. Using computer similations (i) to find suitable methods for studying
pure and mixed systems of interest, and (ii) to determine the line of solidification
in dependence on temperature;
3. To apply the propose expressions for the thermodynamic functions
to important geochemical problems and to determine the global phase diagram
of the exp-6 mixtures.
Statement of the problems
Polar and associating fluid mixtures are frequently used as working
agents in chemical-, energy-, and bio-engineering. As an example from energy
engineering we mention that many alternative refrigerants or heat transformer
working agents are mixtures of polar or associating fluids. In order to
optimize the technical processes, prediction methods for the thermodynamic
properties are required. The most reliable prediction methods are based
on molecular thermodynamics. On this route, the follwing problems have
to be solved:
1. Development of models for the intermolecular interactions;
2. Evaluation of the thermodynamic properties for given intermolecular
interactions by either theory or simulation;
3. Correlation of thermodynamic properties from theory or simulations
by Helmholtz energy equations of state;
4. Development of mixing rules;
5. Development of efficient algorithms to calculate phase equilibria
for mixtures from Helmholtz energy equations of state for their implementation
into CAPE (computer aided process engineering) codes.
