**Bilateral Czech-US project**

**NONADDITIVE INTERACTIONS IN AQUEOUS SOLUTIONS OF ELECTROLYTES:
ROLE OF POLARIZIBILITY AND CROSS INTERACTIONS**

**Researchers:**

**I. Nezbeda,** J. E. Purkinje University

**A. A. Chialvo,** Oak Ridge National Laboratory

[2012 - 2014]

**GOAL:**

The ultimate goal of the project is to develop accurate transferable force fields for simple (mono-, di-, and tri-valent) ions consistent with the polarizable GCP model of water for the description of both bulk and interfacial aqueous systems over a wide range of compositions and thermodynamic states.

**Polymer solutions in an external field: Molecular understanding of electrospinning**

**Principal researcher:** I. Nezbeda

**Co-researcher:** D. Lukas, TU Liberec

[Supported by the Grant Agency of the Czech Republic (2012 - 2015)]

**SUMMARY:**

The project studies polymer solutions subject to an external electric eld with respect to the technology of electrospinning from the free surface. Using molecular modeling and molecular simulations complemented by experiment, an attempt is made to reveal relations between various molecular and/or thermodynamic properties affecting the process of electrospinning. Particularly, given a speci c polymer and solvent, the relations between the conformational behavior of the polymer, concentration and composition of the solvent and strength of the electric eld with the surface tension and diusivity. These results will then provide the input information into semiempirical and theoretical macroscopic methods. The conclusions and recommendations are veri ed by comparison with experimental data obtained also within this project.

**Thermophysical properties of water in unexplored, technologically significant regions**

**Principal researcher: **J. Hruby, Inst. of Thermomechanics, Acad. Sci.

**Participating institution:** Inst. of Chemical Process Fund., Acad. Sci. (Zdimal, Nezbeda)

[Supported by the Gant Agency of the Acad. Sci.: (2009 – 2013)]

__SUMMARY:__

Water has been subject to more studies than any other substance. Yet there are technologically significant regions where its properties are poorly understood. This project focuses primarily on liquid water and solutions of selected salts below the freezing point (supercooled water), and water in nano-droplets. Existing hypotheses include the possibility of phase separation of supercooled water into two liquid phases below the second critical point. Density of supercooled water is only known at 0.1 MPa. Suggested measurements up to 100 MPa will provide first data. A new method and apparatus will be developed. The surface tension of supercooled water and a salt solution will be measured. The surface tension of nano-droplets will be estimated from nucleation experiments. A range of theoretical approaches including phenomenological methods, simplified microscopic models, and molecular simulations, will be used with experimental data to obtain fundamental findings and engineering models.

**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)]

__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)]

__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)]

__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)]

__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)]

__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)]

__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)]

__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.

**Principal researcher:** I. Nezbeda

[Supported by the Grant Agency of the Czech Republic (2001-2003)]

__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.

Theory and applications

**Principal researcher: **I. Nezbeda

[Supported by the Grant Agency of the Academy of Sciences (1999-2002)]

__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.

**Principal researcher:** I. Nezbeda

**Co-researcher:** S. Labik, Inst. of Chemical Technology, Prague

[Supported by the Grant Agency of the Czech Republic (1999-2001)]

__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.

**Co-researchers:**

J. Fischer (Inst. of Environmental and Energy Engng., Agriculture University of Vienna) and I. Nezbeda

[Supported by AKTION - The Czech-Austrian cooperation program (1999 - 2001)]

__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.